Neuro anatomy🧠 Flashcards
What is the cerebrum?
The largest part covering the superior and lateral aspects of the brain, covered in folds of tissue. It is made up of two hemispheres each divided into four lobes.
What is the cerebellum?
The smaller, bulbous structure underneath the posterior part of the cerebrum. Cerebellum means ‘little brain’.
It is lined with many small fissures and is made up of two hemispheres connected by a central ‘vermis’. It connects to the brainstem.
What is the diencephalon?
This area is deep within the brain, beneath the cerebrum but above the brainstem.
What is the brainstem?
This part connects the cerebrum and diencephalon the spinal cord.
What is the frontal lobe?
Contains the primary motor cortex which is involved in planning and executing conscious movement, and the prefrontal cortex which is involved in behaviour, personality and decision making.
What is the temporal lobe?
Contains the primary auditory cortex which is responsible for processing auditory information and the hippocampus which is involved in the formation of memories.
What are the parietal lobes?
Contains the primary somatosensory cortex which is involved in processing sensory information.
What is the occipital lobe?
Contains the primary visual cortex which is responsible for processing visual information.
What does the cerebellum do?
Helps maintain posture and balance, and corrects fine movements
What does the brainstem do?
Connects the rest of the brain to the spinal cord. It contains the nuclei of the cranial nerves and contains vital centres for regulating breathing and cardiovascular function.
What are the gyri?
This term means a ‘fold’ or ‘ridge’. You’ll notice the exterior aspect of the brain is made up of numerous folds of tissue. These folds are called gyri (singular: gyrus). Some have a specific name and a specific function
What are the sulci?
This term means ‘furrow’. The sulci (singular: sulcus) are the furrows, or grooves, in between the gyri.
What is the central sulcus?
This is a large sulcus running in the coronal plane that separates the frontal and parietal lobes. There is a central sulcus on both hemispheres.
What is the lateral sulcus?
This is another large sulcus that runs in the transverse plane. It separates the temporal lobe (below) from the frontal and parietal lobes (above). There is a lateral sulcus on both hemispheres. It is also sometimes called the ‘Sylvian fissure’
What is the insula?
This is a part of the cerebral cortex that can only be seen by opening the lateral sulcus in this way. In some resources, it is considered to be a fifth lobe.
What is the opercula?
This term means ‘lid’ or ‘cover’. It refers to the parts of the frontal, parietal and temporal lobes that cover the insula like lips around a mouth.
What is the longitudinal fissure (interhemispheric fissure)?
This large groove separates the two hemispheres.
What is the corpus callosum and when can you see it?
This is a large bundle of white matter (axons) that connects the two hemispheres. You can see it when separating the longitudinal fissure
What are the olfactory tracts and where are they?
These are nerve fibres carrying information about smell from the nasal cavity. They run along the inferior surface of the frontal lobes on both sides
What are the optic nerves and where are they?
These nerves carry visual information from the retinas of the eyes. They’re also seen on the inferior surface of the frontal lobe and pass posteriorly and medially, to a point where they partly cross over each other (the optic chiasm).
What are the mammillary bodies and what are they a part of?
These rounded structures are found just behind the optic chiasm and pituitary gland. They are part of the diencephalon
What is the hypothalamus and where is it?
This is part of the diencephalon and is only just visible behind the optic chiasm. The mammillary bodies are located on its most inferior surface.
What is the crus cerebri, where are they and what do they form?
this term means ‘feet of the brain’. They are pillars of white matter next to the mammillary bodies that connect the rest of the brain to the brainstem. They form part of the cerebral peduncles which are part of the midbrain.
What is the interpeduncular fossa?
This is the name of the fossa between the cerebral peduncles. It may have a layer of arachnoid mater overlying it on some brain specimens
What are the parts of the brainstem?
-Midbrain
-Pons
-Medulla oblongata
Where is the midbrain?
The most superior part of the brainstem where the crus cerebri are located.
What are the pons?
The large, bulbous, central part of the brainstem
Where is the medulla oblongata?
The most inferior part of the brainstem that tapers down to become the spinal cord inferiorly.
What is the primary motor cortex and where is it?
Most posteriorly in the frontal lobe is the primary motor cortex which is located immediately anterior to the central sulcus. This part of the cortex is involved in execution of motor function (movement).
What is the premotor cortex and where is it?
Immediately anterior to the primary motor cortex is the premotor cortex which is responsible for preparation and planning of movements.
What is the prefrontal cortex and where is it?
More anterior than the premotor cortex. This area is involved in personality, behaviour, problem solving, impulse control and inhibition, and social and sexual behaviour.
What is Broca’s area and where is it?
Broca’s area is found at the inferior frontal lobe of the dominant hemisphere (normally the left) and is important for spoken language production
Where is the parietal lobe?
The parietal lobe extends from the central sulcus (anteriorly) to the parietooccipital fissure (posteriorly).
What is the primary somatosensory cortex?
Immediately posterior to the central sulcus It is responsible for interpretation of sensory information
What is the dominant parietal lobe important for?
The dominant parietal lobe (normally the left) is important for perception, and mathematical and language operations
What is the non-dominant parietal lobe important for?
The non-dominant parietal lobe (normally the right) is important for visuospatial functions.
What is the primary auditory cortex and where is it?
Immediately below the lateral sulcus in the temporal lobe is the primary auditory cortex which is responsible for interpretation of auditory information
What is the hippocampus and where is it?
Inferior and medially in the temporal lobe is the hippocampus which is instrumental in the formation of memory.
What is the amygdala and where is it?
The amygdala is also located deep within the temporal lobe, and it has a role in the perception of fear
What is Wernicke’s area and where is it?
Wernicke’s area is located in the most superior and posterior part of the dominant temporal lobe. It is important in understanding and coordinating spoken language.
What is the occipital lobe and where is it?
The most posterior part of the cerebrum is the occipital lobe, and it contains the primary visual cortex
What is the primary visual cortex responsible for?
Responsible for interpreting visual information received via the optic nerves giving us the perception of sight.
What is the limbic system and what is it made up of?
The limbic system is a group of structures found in the medial margins of the hemispheres including the hippocampus, amygdala and various parts of the cortex. It also includes parts of the diencephalon
What do the structures of the limbic system do?
As a group, they are involved in emotion, memory and behaviour. It has influence over the endocrine functions of the body and parts of it are specifically related to the sensations of fear, pleasure and rewarding behaviours
What is the clinical significance of knowing the different lobes of the brain?
Being aware of the functions of each lobe of the brain allows clinicians to localise a problem within a patient’s brain before confirming this with neuroimaging (such as CT or MRI scans). For example, if a patient is suspected to have suffered a stroke (disruption to blood supply to a part of the brain) and one of their symptoms is blindness, this could indicate that the occipital lobe is affected. Similarly, if their symptoms are paralysis of their right side and slurring of speech, this may indicate the left frontal lobe is affected.
What is a homunculus and what are the two types?
Within the primary motor and sensory cortices, different parts of the body are represented by different parts of the gyri. When displayed pictorially, this ‘mapping’ of specific parts of the body to parts of the cortex is called a homunculus. There is a homunculus for the motor and sensory cortices, but they are largely similar.
Where are the face and mouth represented in the brain?
On the lateral aspects of the primary motor and somatosensory cortices
Where are the upper limb and torso areas located in the brain?
The most superior part of the cortex.
What area of the brain represents the feet?
Most medial parts of the cortices (deep in the longitudinal fissure)
When is it relevant to think about the homunculus?
It is relevant when discussing lesions affecting the cortex, such as a stroke, which may only affect the lateral aspect of the hemisphere, instead of the superior or medial aspects, for example.
What are the meninges?
The meninges are three layers of tissue that envelop the brain and spinal cord. Their full names include ‘mater’ but clinically, they are often referred to by just their first part.
What is the dura mater?
Most external, lying against the skull. It is fibrous, thick and does not stretch.
What is the arachnoid mater?
The intermediate layer, it is much thinner and more flexible and resembles a spider’s web, hence the name
What is the pia mater
Most internal, it lies on the surface of the brain. It is very thin such that it cannot be seen with the naked eye.
What are the two layers of the dura?
- The outer endosteal layer is adherent to the interior of the skull.
- The inner meningeal layer completely envelops the brain and spinal cord.
What is different about the inner meningeal layer?
The meningeal layer peels away from the endosteal layer in certain places and folds down into the brain to form a double layer of dura that separates certain parts of the brain.
What is the falx cerebri?
A double layer of folded dura lying in the longitudinal fissure that separates the two cerebral hemispheres.
What is the tentorium cerebelli?
The tentorium cerebelli is a double layer of folded dura that separates the occipital lobe from the cerebellum
What is the falx cerebelli?
The falx cerebelli, like the falx cerebri, separates the two lobes the cerebellum. It is, however, much less pronounced
What are the dural venous sinuses?
There are small channels where the outer endosteal layer and inner meningeal layer of the dura are briefly apart from each other, or where the inner meningeal layer folds back on itself leaving a small space. These channels are filled with venous blood
What is the superior sagittal sinus?
Formed in the space between the two layers of the dura, this sinus is located superiorly and runs the along the top of the brain in the sagittal plane.
What is the inferior sagittal sinus?
This is a smaller version of the superior sagittal sinus and runs in the same direction but is located inferior to it. It is formed as the meningeal layer of dura that forms the falx cerebri folds back on itself in the longitudinal fissure. It lies on top of the corpus callosum.
What is the straight sinus?
This dural venous sinus is found where the falx cerebri connects to the tentorium cerebelli posteriorly and allows venous blood to drain backwards from the inferior sagittal sinus.
Where are the the transverse sinuses?
Found on both lateral aspects extending from the tentorium cerebelli around the side of the skull.
What are the sigmoid sinuses?
These s-shaped sinuses connect the transverse sinuses to the internal jugular veins outside the skull to drain venous blood from the brain
What is a confluence of sinuses?
Where the straight sinus meets the transverse sinuses and the superior sagittal sinus. It is found at the most posterior aspect of the skull and often leaves an impression in the internal aspect of the skull.
What are the cavernous sinuses?
These ‘cave-like’ sinuses are found anteriorly, either side of the sella turcica of the sphenoid bone. The internal carotid artery passes through it, along with some important nerves.
What is the arachnoid mater?
The arachnoid is a single layer that loosely follows the contours of the meningeal layer of the dura. During dissection, it resembles a very thin, transparent layer of cling film.
What is the the subarachnoid space?
Between the arachnoid and the pia below is the subarachnoid space which contains cerebrospinal fluid (CSF).
What are the cisterns?
In some areas, the arachnoid spans between the gyri of the brain, leaving a covering over the sulcus. This forms a sealed space filled with CSF. These spaces are known as ‘cisterns’.
What are the main features of the pia mater?
As mentioned, the pia is so thin it cannot be seen without a microscope. It is tightly adhered to the brain and spinal cord and plays a vital role in forming the blood-brain barrier
What is the blood-brain barrier?
At the capillary level, the pia fuses with the endothelial cells of the capillaries, forming a specialised layer of pia and endothelial cells known as the blood-brain barrier
It limits the passage of certain molecules into the brain and spinal cord to protect them from harmful substances
What are the four key features of the blood brain barrier?
- The endothelial cells are tightly bonded together to prevent molecules passing between them.
- The basement membrane of the capillaries in the brain and spinal cord lacks fenestrations (small holes) that are found elsewhere in the body.
- Further specialised cells known as ‘pericytes’ wrap around the endothelial cells to regulate blood flow and permeability.
- CNS cells called ‘astrocytes’ have specialised projections called ‘end feet’ that further wrap around the capillaries to restrict flow of certain molecules.
What is meningitis?
Inflammation of the meningeal layers is called meningitis. It is often caused by infection due to a viral or bacterial organism. Symptoms include headache, stiffness of the neck and photophobia (bright lights causing discomfort). Viral meningitis usually causes more mild symptoms and resolves on its own. Bacterial meningitis is much more serious and requires treatment with intravenous antibiotics. To confirm the diagnosis, a sample of CSF is required to be tested. To collect this, a small needle is inserted into the subarachnoid space in the lumbar region of the spine. This is known as a lumbar puncture or ‘spinal tap’.
What is intrameningeal bleeding?
Spontaneously, or after head trauma, bleeding can occur between the meningeal layers. The three main types of bleeds are:
Extradural haemorrage
Subdural haematoma
Subarachnoid haemorrhage
What is an extradural haemorrage?
Blood is located outside the dura, but inside the skull. The characteristic pattern on a CT scan is that of an oval or convex shape, often located at the lateral aspect of the brain. The reason the blood forms this shape is because the endosteal layer of the dura is tightly stuck to the inside of the skull, meaning blood trapped outside of it bulges inwards and cannot spread around the side of the brain. Extradural blood is arterial, and a common cause of an extradural haemorrhage is traumatic damage to the middle meningeal artery located on the lateral aspects of the skull. This region is sometimes referred to as the ‘temple’
What is a subdural haematoma?
Blood is located deep to the dura, but superficial to the arachnoid. The characteristic pattern on a CT scan is that of a crescent or concave shape, often located at the lateral aspect of the brain. Unlike in the extradural space, the arachnoid and dura are not adherent to each other, so blood can easily spread around the sides of the brain causing the crescent appearance. Subdural blood is venous, and bleeding is often caused because of stretching of bridging veins that are carrying venous blood from the brain to the dural venous sinuses. Any process or illness that causes the brain to shrink in size causes these bridging veins to become stretched, which is why subdural haematomas are more common in the elderly or patients suffering from alcoholism.
Describe a subarachnoid haemorrhage
Blood is located deep to the arachnoid, but superficial to the pia. Blood leaks into the subarachnoid cisterns, mixing with the CSF, sometimes causing a white star-shaped pattern on a CT scan. Subarachnoid blood is usually arterial and may be caused by a traumatic head injury or rupture of an aneurysm of one of the cerebral arteries. The classic symptom at presentation of spontaneous subarachnoid haemorrhage is sudden-onset severe headache, often termed a ‘thunderclap’ headache. Diagnosis may be confirmed by CT scan or by the presence of blood in the CSF. This can be sampled with a lumbar puncture.
What is the difference between a haemorrage and a haematoma?
A haemorrhage is an active bleed, whereas a haematoma is a collection of blood without active bleeding
Why is bleeding inside the skull such a problem?
The main complication of bleeding inside the skull is the resultant increase in intracranial pressure. As the skull is a fixed size in adults, and cannot expand, if there is a build-up of blood inside it, the brain becomes compressed. Eventually, this will lead to impairment of functions of the brain, and ultimately, death
What is a classic presentation of an extradural haemorrage?
The classic presentation of an extradural haemorrhage, for example, is that of a patient who sustains a head injury, and then retains consciousness for a ‘lucid’ period, before becoming comatose. This is explained by the brain initially compensating for the bleed by becoming compressed, but eventually, it reaches its limit of compensation, and the patient loses consciousness. If a collection of blood or another space-occupying lesion, such as a tumour, is causing compression of the brain, you may be able to see a deviated falx cerebri or compressed lateral ventricle on at CT scan
What is coning?
As intracranial contents are compressed by the build-up of pressure inside the skull, parts of the brain may be pushed aside and can herniate into other areas.
What are some examples of coning?
For example, part of the temporal lobe called the uncus may be forced under the tentorium cerebelli (uncal herniation), or certain parts of the cerebellum called tonsils may be forced out of the foramen magnum (tonsillar herniation).
What happens if intercranial compression is not treated properly?
This pressure will restrict blood supply to compressed parts of the brain, and is often fatal if not treated promptly
What arteries supply the brain?
The arterial supply to the brain comes from two pairs of arteries: the internal carotid arteries, and the vertebral arteries
The vertebral arteries supply approximately 20% of blood to the brain, mainly the posterior parts such as the occipital lobe, cerebellum and brainstem. The internal carotid arteries supply the remaining 80% including the rest of the cerebrum and diencephalon.
What is the circle of Willis?
The internal carotid and vertebral arteries ascend in the neck and enter the skull, they form a circular network known as the circle of Willis, or cerebral arterial circle
This network of arteries can be seen on the inferior surface of the brain lying on the brainstem and frontal lobe
Where are the internal carotid arteries?
ascending upwards from the neck.
Where are the vertebral arteries?
Ascending upwards through the cervical vertebrae
How is the basilar artery formed?
A singular artery formed by the unison of the two vertebral arteries. It gives off small pontine arteries to supply the brainstem as it travels along its surface
How are the posterior cerebral arteries formed?
Formed by the bifurcation of the basilar artery, these arteries pass posteriorly after their formation
How are the middle cerebral arteries formed?
The continuation of the internal carotid arteries after they have entered the skull. These arteries pass into the lateral sulcus and give off many branches to both superficial and deep brain tissue.
What are the anterior cerebral arteries?
Branches of the internal carotid arteries as they enter the skull. These arteries pass anteriorly and then wrap backwards over the corpus callosum.
What do the posterior communicating arteries do?
Branches of the internal carotid arteries as they enter the skull. These arteries pass anteriorly and then wrap backwards over the corpus callosum.
What does the anterior communicating artery do?
Joins the left and right anterior cerebral arteries
What are the 3 pairs of cerebellar arteries?
o Anterior inferior cerebellar arteries (AICA).
o Posterior inferior cerebellar arteries (PICA).
o Superior cerebellar arteries (SCA).
Why do we need to know the vascular territories of the circle of willis?
The major arteries of the circle of Willis supply a specific area of the brain. It is important to know which parts they supply as this can help identify which artery is likely to be compromised if certain neurological functions are lost in patients who have suffered a stroke
Where does the anterior cerebral artery (ACA) supply?
These vessels supply the medial aspects of the frontal and parietal lobes, and a strip of cortex on the superior aspect. This includes the motor and somatosensory cortex responsible for the lower limbs. They also supply some of the anterior structures of the diencephalon
Where does the middle cerebral artery (MCA) supply?
These large vessels supply the vast majority of the lateral aspects (outside) and deep parts of the hemispheres. This includes the parts of the motor and somatosensory cortices responsible for the face, arms and trunk, and a structure called the internal capsule that transmits all fibres to and from the cortices. The MCA also supplies some of the structures of the diencephalon.
Where does the posterior cerebral artery (PCA) supply?
These vessels mainly supply the occipital lobe which contains the visual cortex, but also a small portion of the inferior temporal lobe.
Where does the basilar artery supply?
This large singular vessel carries arterial blood from the vertebral arteries to the circle of Willis. It gives off small branches to supply the pons. As the pons forms part of the pathway of between the brain and spinal cord, disruption of the basilar artery can potentially threaten the function of all ascending and descending fibres including all motor control and sensation from the neck down.
Where do the cerebellar arteries (AICA, PICA, SCA) supply?
These vessels mainly supply the cerebellum, but in addition to the basilar artery, they also supply parts of the brainstem.
What does the anterior circulation include?
including the anterior and middle cerebral arteries
What does the posterior circulation include?
Including the posterior cerebral, basilar and cerebellar arteries
What is a stroke?
A stroke is an interruption to the blood supply of part of the brain leading to a neurological deficit that lasts longer than 24 hours. Strokes may be ischaemic (caused by obstruction of a vessel by a thrombus or embolus and subsequent downstream ischaemia) or haemorrhagic (caused by rupture of a blood vessel leading to compression of nearby structures by the accumulation of blood).
What is a berry aneurysm?
Aneurysms are deformities in arterial vessel walls causing them to balloon and make them prone to rupture. Berry aneurysms, named after their characteristic appearance, may be found in the cerebral circulation on the sides of cerebral arteries. They are often asymptomatic until they rupture. A ruptured berry aneurysm most often causes a subarachnoid haemorrhage, leaking arterial blood into the subarachnoid space. Symptoms include a severe, sudden-onset headache, vomiting or a reduction in a patient’s conscious level.
Why is venous drainage of the brain unique?
The venous drainage of the brain is unique in that venous blood is drained from smaller cerebral veins into large dural venous sinuses before passing back into veins to be returned to the heart
What is the progression of the venous drainage of the brain?
- Cerebral venous blood first drains into internal cerebral veins, which are located deep within the brain tissue.
- The internal cerebral veins then drain into larger external cerebral veins which can be seen on the surface of the brain.
- The external cerebral veins then drain into the dural venous sinuses
- The dural venous sinuses can drain the blood into extracranial veins
What are the two routes of drainage from venous sinuses into extracranial veins?
o The sigmoid sinuses become the internal jugular veins as they exit the skull.
o Emissary veins cross the endosteal layer of dura and drain the venous blood into the bones of the skull.
What is a cavernous sinus?
One of the dural venous sinuses that is found behind the orbit (eye socket) on both sides is called the cavernous sinus.
What is the clinical relevance of the cavernous sinus?
It is clinically relevant because the internal carotid artery and several important nerves pass through it: the oculomotor nerve (CN III), trochlear nerve (CN IV), ophthalmic nerve (CN V1), maxillary nerve (CN V2) and abducens nerve (CN VI). Venous blood draining from the face can potentially drain into the cavernous sinus, thereby providing a connection for superficial infection of the face to reach intracranial structures. Infection in the cavernous sinus can lead to meningitis or thrombosis. A thrombosis here will cause an increase in pressure and compress these nerves leading to problems with eye movements and sensation over the face.
What is venous sinus thrombosis?
Just like other vessels in the body, blood can clot within the dural venous sinuses. If this occurs, drainage of venous blood will be compromised, meaning there will be an increase in intracranial pressure causing a headache and potentially a significant and devastating compression of intracranial structures
What are the ventricles of the brain?
There are central cavities within the brain that are filled with cerebrospinal fluid (CSF). These cavities are called ventricles and are joined to each other. They are continuous with the subarachnoid space meaning the CSF can surround the brain and spinal cord.
Why do we have ventricles?
It means the brain is submerged in a thin layer of CSF which provides a degree of physical protection, and mechanism for transfer of certain substances in and out of the brain tissue.
What produces CSF and where?
CSF is primarily produced in the lateral ventricles by a group of specialised cells called the choroid plexus. The lateral ventricles are located within the cerebral hemispheres
What happens after the CSF has been produced?
It then flows out of the lateral ventricles via the interventricular foramen to reach the third ventricle. The third ventricle is a very thin chamber in the midline separating the two sides of the diencephalon.
What happens to the CSF after being in the third ventricle?
CSF then passes out of the third ventricle via the cerebral aqueduct into the fourth ventricle which is diamond-shaped and located posterior to the brainstem, but anterior to the cerebellum
What happens when the CSF leaves the ventricular system?
Leaves the ventricular system either by passing inferiorly via the central canal to fill the subarachnoid space around the spinal cord, or posteriorly and laterally (via the median aperture of Magendie and lateral apertures of Luschka, respectively) to enter the subarachnoid space that surrounds the brain.
What are subarachnoid cisterns?
In certain areas around the brainstem and diencephalon, there are larger pockets of CSF in the subarachnoid space called subarachnoid cisterns
On a CT scan, blood may be identified in the subarachnoid cisterns if there is bleeding into the subarachnoid space.
What are arachnoid granulations?
These are outpouchings similar in shape to a mushroom, that push out of the subarachnoid space around the brain into the dural venous sinuses. CSF diffuses across the wall of the arachnoid granulations to enter the bloodstream here.
What are the main divisions of the primitive brain?
Hindbrain- pons and medulla
Midbrain
Forebrain- Telencephalon and diencephalon
Planes and directions of the brain
Caudal (hind) -> rostral (neck)
Horizontal, sagittal (through nose), coronal ( thru ears)
What is white matter made of?
Axons and myelin (made of fat
What are association fibres?
Remain within 1 hemisphere
Group of fibres that communicate within the hemisphere
Comisural fibres
Cross between hemispheres
anterior commisure- helps with identifying site of interest
Corpus callosum- main communiscto
Projection fibres
Go down into spinal cord and then up
What do the 6 layers of the neocortex do?
1+2. Input from other cortical areas
3. Projects to other cortical areas
4. Input from thalamus
5. Projects to brainstem and spinal cord
6. Projects to thalamus
What is the general rule of what parts of the brain control what types of things?
Back of brain does sensory stuff
Front of brain does output stuff
Describe the brain asymmetry
Frontal petalia is only on right
occipital petalia is only on the left
(ADD TO THIS)
What are the areas created by the dura mater?
Falx cerebri
Tentorium cerebelli
Tentorial incisure
Straight sinus
Inferior sagittal sinus
Superior sagittal sinus
Transverse sinuses
Falx cerebelli
What is the primitive streak?
The faint streak which is the earliest trace of the embryo in the fertilized ovum of a higher vertebrate
Describe the myelination of white matter in the brain
White matter is insulated by Oligodendrocytes\Schwann cells
Allows the electrical signals to travel faster
Your myelinated brain stem keeps you breathing
Unless you have an abnormal PHOX2Bgene
Where do neurons grow and migrate to
Neurons arise in the germinal matrix
Migrate to cortical sub plate and wait
Key facts about the brain
Is only about 1.3 kg in weight
Thus only about 2.3% of you body mass
Uses 20% of blood supply and oxygen
Generates about 23 watts (Joules/second)
The neo-cortex and language centres are 76% of your brain
Key reflexes in infants
Rooting Reflex: turn head and mouth in direction of stroking of cheek
Sucking Reflex: babies will suck object that touches the lips
Moro (Startle) Reflex: back arches, legs and arms are flung out and then brought back toward chest into a hugging motion
Grasping (Palmar) Reflex: babies grasp objects pressed against palms
Stepping Reflex: babies will mimic walking when help upright
Babinski Reflex: infant fans toes when feet are stroked
Tonic-Neck Reflex: infant turns head to one side, extending arm and leg
Key facts about vision in babies
Best see objects 7 to 9 inches from eyes
Lack peripheral vision
Able to track movement within one day of birth
Convergence does not occur until 7 or 8 weeks
Cones less developed than rods at birth, but at 3 months, can see most visible colours
Key facts about hearing in babies
Middle and inner ear mature in shape and size. So hear remarkably well
Show preference for mothers’ voice
Key facts about smell in babies
Smell well developed at birth
Demonstrate facial expressions to different odours
Aversion for noxious and preference for pleasant odours
Recognize familiar odours
Learned preference for mother
Key facts about taste in babies
Tastes sensitive at birth
Discriminate between salty, sour, and bitter tastes
Prefers sweet – works as an analgesic
Which direction is development in?
Cranial to caudal
Proximal to distal
Simple to complex
Ambidextrous until 3 years old
What does the left side of the brain do that the right side doesn’t?
Verbal, Speaking, Reading, Thinking, Reasoning, Processes information sequentially, One piece of information at a time
What does the right side of the brain do that the left side doesn’t?
Nonverbal, Spatial relationships, Patterns/Drawing recognition, Music, Emotional expression, Processes information holistically
What is lissencephaly?
smooth brain, neuronal migration disorder
Outline ventricular haemorrage in foetal development
Around 80% of babies less than
32 weeks have a normal scan
Around 14% have small bleeds
Around 6% of babies less than
32 weeks have scans like these
Neonatal brains display significant plasticity
Red flags in babies
Syndromic children/Dysmorphisms
History of brain injury
Any loss of skills at any age
Visually not fixing or following an object
Hearing loss
Low or High muscle tone
Squint after 3 to 4 months (6th nerve)
Cannot hold object placed in hand at 5 months
Red flags in children
Can’t sit unsupported by 12 months
Boys not walking by 18 months
Girls not walking by 2 years
Persistent toe walking
No speech by 18 months
Can’t point at object to share interest with others by 2 years
Handedness before 3 years old
What are some neuroimaging techniques?
Plain X-rays
Computed Tomography – CT
Magnetic Resonance Imaging – MRI
Cerebral Angiography
Myelography
Nuclear Medicine
Describe CT scanning
Dose of Radiation
1 CT head = 100 chest X-rays
Limited anatomical detail
Acquired in axial plane
Volume data
May require iodinated contrast media
Potential for allergic reaction
Better than MRI for demonstrating bone & calcification (craniopharyngioma/meningioma)
Seconds
Describe MRI
Multiple planes possible
Excellent anatomical detail
Contrast injection may required
Strong magnetic field – in some patients MRI is contraindicated
Noisy & claustrophobic
Longer scan times than CT
No ionising radiation
Infections and inflammation of the brain
Ring enhancing lesion- could be a brain tumour, plaque of de-myelination or abscess
MS active inflammation incomplete ring enhancement
Neuroborrelosis- Lyme disease
Types of brain tumour
Low grade glioma
High grade glioma
Oligodendroglioma
Leukaemic deposit
Meningioma
Metastases from other cancers
Auditory system general areas and what do they contain?
Outer ear- air
Middle ear- air
Inner ear- fluid
Central auditory pathways
The pinna
Ear shape is unique to ppl
folds collect soundwaves and channel into external- auditory canal
Filters out low frequency sound instead of high frequency sounds
Outer ear: tympanic membrane
Ear drum
What is contained in the middle ear?
Contains bones- malleus, incus, stapes
Contains muscles- Tensor tympani and stapedius
Tubes- eustachian tube
Describe the vestibulocochlear apparatus
Set of fluid filled scs
cochlear- hraring
labyrinth: balance
Innervation: vestibulocochlear nerve
Describe the cochlear
2.5 turns fluid filled bony tube
Describe the basilar membrane
Narrow at base- wide at apex
Stiff at base- floppy at apex
High frequencies detected at base
Low frequencies at apex
Concept called tonotopy
Organ of cor
CNS cell types
Neurons and
glia
Neurons
Specialised
Skeletal muscle basic structure
Myofibres arranged in fascicles
Connective tissue
Basement membrane
Vascular supply
Innervation
Myotendinous junction
Types of connective tissue in muscles
Epimysium
Perimysium
Endomysium
What does the basement membrane do in muscles
Surrounds individual myofibres
Collagen, glycoproteins and proteoglycans
Roles in tensile strength, regeneration, development
What does the myotendious junction do?
Transmits force of muscle contraction to the tendon
Skeletal muscle innervation
Each fibre innervated by one nerve, with cell bodies in anterior horn of spinal cord or brainstem
One neuron innervates multiple muscle fibres – motor unit
Neuromuscular junction
Proprioception – length and tension
Neuromuscular junctions in skeletal muscle
Synapse – rapid transmission of depolarising impulse
Acetyl choline – binds post-synaptic AChR
Describe proprioception in skeletal muscle
length and tension
Muscle spindles – encapsulated intrafusal fibres. Mediate stretch reflexes and proprioception
Golgi tendon organs - tension
Sites of pathology affecting the muscle and nerve
MND
Peripheral neuropathy
Neuromuscular transmission defects
Primary muscle disease
Skeletal muscle histology
Can be studied by muscle biopsy
Requires the use of frozen sections and good orientation
EM
Molecular tests
WHat do we use to stain skeletal muscle
Enzyme histochemistry- reveals different fibre types
It is why it has to be fresh
Incl. NADH and ATPase
Muscle fibre types
-Slow twitch (red fibres) – type 1, oxidative, fatigue resistant
-Fast twitch – fatigue rapidly but generate a large peak of muscle tension
-2A – glycolytic and oxidative (intermediate)
-2B – glycolytic (white)
Describe the motor unit
-Motor neuron (lower) and the fibres it innervates
-Neuron and its fibres of same type
-Fibre type dependent on neuron
-Size of motor unit varies between muscles
Describe how motor units are altered in denervating diseases
-Loss of innervation causes fibre atrophy
-Collateral sprouting from adjacent motor units allows reinnervation
-Larger motor units result – this can be detected electrophysiologically
-Conversion of fibres results in fibre type grouping
What is fibre type grouping?
What is a sarcomere?
Sarcomere – basic unit of contraction
Repeating arrangement of thick (myosin) and thin filaments (actin)
Proteins in myofibrils
-alpha-actinin
-Titin
-Nebulin
-Desmin (links myofibrils to each other and the sarcolemma)
What is linked to actin?
-Troponin/tropomyosin complex – Calcium regulation
What is sliding filament theory?
- Myosin heads bind actin
- Binding of ATP allows release and hydrolysis to ADP allows movement of myosin head. ADP released during power stroke.
- Sarcomeric shortening due to sliding of the filaments NOT change in length of either actin or myosin
- Initiated by increased cytosolic Ca2+
- Accessory proteins
What are the accessory proteins in muscle fibres?
-Troponin/tropomyosin – mediate Ca2+ regulation
-Maintaining architecture of the filament – e.g. nebulin, titin
What is the requirement for energy in muscle fibres?
High energy requirement from ATP
Creatine phosphate a short term energy store
CP replenished by creatine kinase (CK)
CK is released on muscle fibre damage
Measurement of serum CK clinically useful
Describe mitochondrial cytopathies
Mitochondrial DNA - Circular ds DNA, Maternally inherited
Diverse clinical presentations with an emphasis on CNS
E.g. MERRF, MELAS, CPEO
Mutations in either mitochondrial or nuclear DNA
Mitochondrial mutations – maternal inheritance
Heteroplasmy
How would you diagnose mitochondrial cytopathies from a muscle biopsy?
-Ragged red fibres
-Electron transport chain deficits – cytochrome oxidase negative fibres
-Abnormal mitochondrial morphology
-Gene defects
What is gomori trichrome?
Ragged red fibres
Maintenance of membrane stability
Distrophin
Describe dystrophies and defects of sarcolemmal related proteins
-Dystrophies are genetically determined, destructive and mainly progressive disorders of muscle
-There are many types of dystrophy
-Defects of proteins that confer stability to the sarcolemma are one group of causes.
Describe dystrophin and what a defect causes
-A large protein encoded by a 2.4 million bp gene on Xp21
-Confers stability to the muscle cell membrane
-Deletion resulting in disruption of the reading frame results in Duchenne
-In Becker’s, and in-frame deletion results in a truncated product
Describe neuromuscular transmission
Nerve impulse results in the release of acetyl choline from synaptic vesicles
ACh binds to its receptor
Cation entry results in depolarisation, the end-plate potential
An action potential travels across the muscle cell membrane and into the T-tubule system
Calcium is released from the sarcoplasmic reticulum leading to activation of contraction
Dissociated ACh is hydrolysed by acetyl cholinesterase in the NMJ
Describe disorders of Neuromuscular transmission
-Myasthenia gravis – variable weakness, progressive with sustained effort, eye signs – ptosis
-Autoimmune disease
-Anti-AChR antibodies resulting in a reduction in ACh receptors
-Acetyl cholinesterase inhibitors can improve muscle function
Describe myelinated fibres
In the PNS, the Schwann cell is responsible for the myelin sheath
Each Schwann cell is responsible for one segment of myelin
Nodes of Ranvier lie between adjacent myelin segments
The node is where depolarisation of the membrane occurs
Myelination allows saltatory conduction
Describe peripheral neuropathies
-Damage to motor or sensory neurons – neuronopathies
-Damage to axons – axonopathies
-Selective damage to myelin sheaths - demyelination
Peripheral nerve
Fascicles of perineurium surrounded by fatty connective epineurium
Describe axonal degeneration / regeneration – Wallerian degeneration
-Injury to axon – distal fragmentation
-Globules of myelin and axon debris form, initially within Schwann cell
-Axonal sprouts form from proximal part of damaged axon and grow along columns of proliferating Schwann cells
-Regenerated axons can remyelinate
Describe the bones of the base of the skull?
The base of the skull is formed from several individual bones joined by fibrous joints known as sutures. Several of the names of the bones match the lobes of the brain that are in contact with them.
Describe the three cranial fossae
Depressions in the base of the skull
- Anterior cranial fossa
- Middle cranial fossa
- Posterior cranial fossa
What are cranial foramina?
Within each cranial fossa are several small holes which allow nerves, arteries and veins to pass in and out of the skull. These are known as cranial foramina (singular: foramen).
Describe the anterior cranial fossa
he frontal lobes rest in the anterior cranial fossa, and it is formed of 3 bones:
- Orbital part of frontal bone
- Cribriform plate
- Lesser wings of sphenoid bone
Describe the orbital part of the frontal bone
The two rounded elevations are the spherical cavities of the bony orbits, where the eyes are located.
Describe cribriform plate and the crista galli of the ethmoid bone
The cribriform plate (meaning ‘sieve-like’) has many small holes for passage of olfactory nerves. The crista galli (meaning ‘rooster’s crest’) is the vertical protrusion in its centre.
Describe the lesser wings of the sphenoid bone
The sphenoid bone (meaning ‘wedge-shaped’) has smaller (lesser) superior wings, a body in its centre and larger (greater) inferior wings.
Where is the only foramen in the anterior cranial fossa?
Cribriform plate – transmits olfactory fibres that allow our sense of smell.
Describe the middle cranial fossa
The temporal lobes rest in the middle cranial fossa, and it is formed of two bones:
- Petrous and squamous parts of the temporal bone
- Greater wing and body of the sphenoid bone
Describe the Petrous and squamous parts of the temporal bone
The petrous (meaning ‘rock-like’) is the very hard and bulbous inferior and medial part of the temporal bone. The inner and middle ear cavities are located inside it. The squamous (meaning ‘scale-like’) is the flat, lateral part of the temporal bone.
Describe the greater wing and body of the sphenoid bone
The body of the sphenoid bone includes a small, rounded cavity about the size of the end of your finger called the pituitary fossa. It is also known as the sella turcica (meaning ‘turkish saddle’) and it is where the pituitary gland is located
What are the foramina located on each side of the middle cranial fossa?
- Optic canal
- Superior orbital fissure
- Foramen rotundum
- Foramen ovale
- Foramen lacerum
- Foramen spinosum
Describe the optic canal
Transmits the optic nerve into the bony orbit.
Describe the superior orbital fissure
Transmits several nerves that provide motor innervation (oculomotor, trochlear and abducens nerves) and sensation (ophthalmic branch of the trigeminal nerve) to the orbital region.
Describe the foramen rotundum
Transmits the maxillary branch of the trigeminal nerve.
Describe the foramen ovale
transmits the mandibular branch of the trigeminal nerve.
Describe the foramen lacerum
The internal carotid artery exits the carotid canal through this foramen to enter the skull.
Describe the foramen spinosum
Transmits the middle meningeal artery.
What is in the posterior cranial fossa and what bones make it up?
- Internal auditory meatus
- Jugular foramen
- Hypoglossal canal
- Foramen magnum
Describe the internal auditory meatus
Transmits the vestibulocochlear and facial nerves into the inner ear cavity.
Describe the jugular foramen
Transmits the glossopharyngeal, vagus and accessory nerves, and the internal jugular vein.
Describe the hypoglossal canal
Transmits the hypoglossal nerve
Describe the foramen magnum
This central singular foramen is very large and allows central nervous system fibres to leave the skull and become the spinal cord.
Describe the potential consequences of skull fracture due to traumatic head injury
· The brain itself could be directly damaged by the force.
· The fracture could extend through some of the foramina and damage the structures passing through them.
· The dura and arachnoid meninges may be damaged which could cause CSF to leak out. Clinically, this may be suspected if a clear liquid is seen to be leaking from the patient’s nose or ears after a head injury.
· Significant bleeding may occur from the fractured bone or due to damage to intracranial arteries, veins or dural venous sinuses.
Describe the pterion
The pterion is an area of the skull often referred to as the ‘temple’ and it is located just lateral and posterior to the eyebrow. It is a shallow depression where four bones of the skull converge: the frontal, temporal, sphenoid and parietal bones. Because of this, it is considered to be the weakest part of the skull and prone to fracture if struck. Unfortunately, the middle meningeal artery lies immediately behind the pterion, therefore traumatic injuries to this area may cause an extradural haemorrhage.
Describe crainiosinotosis
The sutures (joints between the bones) of the skull do not completely fuse until a child is around two years old. This allows the brain to increase in size as the child grows quickly in infancy. If certain sutures of the skull fuse together too early, as the brain continues to grow it will cause the skull to become misshapen and this is called craniosynostosis. The skull may be elongated in the longitudinal, transverse or oblique planes, depending on which sutures fuse before they are supposed to.
Describe burr holes
If there is a build-up of pressure within the fixed confines of the skull, this must be relieved, or the brain will eventually be compressed which can lead to death. Common causes of a build of pressure in this way may include intracranial bleeding (such as an extradural haemorrhage) or a brain tumour. To relieve the pressure quickly, a small hole (about 10-15 mm diameter) can be drilled into the skull. This allows the brain to expand enough to relieve the pressure, or it can be used to directly drain the bleeding that’s causing the pressure build-up.
Describe a craniotomy
To perform surgery on the brain, a larger hole may be needed. This is called a craniotomy, and a circular piece of the skull is removed. This may be replaced later, or a prosthetic implant may be used to close the craniotomy instead.
Describe the bony orbits of the eye
The two orbits are shaped like cones, with a broad opening at the front, tapering to a narrow part at the back. They are formed of several bones: the larger frontal, sphenoid, zygomatic and maxillary bones, and the smaller ethmoid and lacrimal bones.
What structures are found in the orbits?
- Eye
- Extraocular muscles
- Nerves
- Fat
- Lacrimal gland
Describe the extraocular muscles
Six small but distinct muscles that move the eye to direct our vision where we want it, and a seventh muscle responsible for retracting the upper eyelid.
Detail the nerves that are found in the orbits
Including the optic nerve for vision, the oculomotor, trochlear and abducens nerves that control the extraocular muscles, and the ophthalmic branch of the trigeminal nerve which supplies sensation to eye and forehead.
What is the lacrimal gland?
Found in the superior and lateral part of the orbit, this gland produces tears to lubricate the anterior surface of the eye.
What are the foramina in the orbit?
Optic canal, superior orbital fissure and inferior orbital fissure.
Outline the extraocular muscles
There are seven extraocular muscles. All have distinct functions and two have a unique nerve supply. Some muscles have additional actions on the eye due to the angle at which they attach to the eye. The dysfunction of one of the muscles or nerves supplying them will produce characteristic findings when examining the patient.
Mnemonic to remember the nerves that supply the extraocular muscles
LR6SO4 –
lateral rectus is supplied by cranial nerve 6, superior oblique is supplied by cranial nerve 4. The rest of muscles are supplied by cranial nerve 3
Terms used to describe the movement of the eye
· Elevation – to look up.
· Depression – to look down.
· Adduction – to look medially.
· Abduction – to look laterally.
· Extorsion – to rotate the eye, so the top of the eye rotates laterally.
· Intorsion – to rotate the eye, so the top of the eye rotates medially.
What is conjugate eye movements?
Both eyes do not necessarily perform the same movement when you change where you look. For example, to look to your left with both eyes, your left eye needs to abduct, but your right eye will need to adduct. This is known as conjugate eye movements.
Outline the levator palpebrae superioris
Nerve supply- Oculomotor nerve (CN III)
Action on eye- Elevate superior eyelid
Findings if non-functional- Ptosis (drooping eyelid)
Outline the superior rectus muscle
Nerve supply- Oculomotor nerve (CN III)
Action on eye- Elevate, intort, adduct
Findings if non-functional- unable to elevate
Outline the inferior rectus muscle
Nerve supply- Oculomotor nerve (CN III)
Action on eye- Depress, extort, adduct
Findings if non-functional- unable to depress
Outline the medial rectus muscle
Nerve supply- Oculomotor nerve (CN III)
Action on eye- Adduct
Findings if non-functional- Unable to adduct
Outline the lateral rectus muscle
Nerve supply- Abducens nerve (CN VI)
Action on eye- Abduct
Findings if non-functional- Unable to abduct
Outline the superior oblique muscle
Nerve supply- Trochlear nerve (CN IV)
Action on eye- Intort, depress, abduct
Findings if non-functional- Unable to depress if eye is adducted
Outline the inferior oblique muscle
Nerve supply- Oculomotor nerve (CN III)
Action on eye- Extort, elevate, abduct
Findings if non-functional- Unable to elevate if eye is adducted
What is the common tendinous ring?
The four recti extraocular muscles originate at the back of the orbit on a fibrous ring known as the common tendinous ring (or annular tendon, or annulus of Zinn)
What is intorsion and extorsion?
The additional functions of intorsion, extorsion and adduction are secondary effects caused by the angle at which these two muscles pull on the eye. When looking at the orbits from above, if you draw a line through the centre of both orbits (which represents the angle at which these muscles pull on the eye) you’ll notice these two lines are not parallel and they do not point directly forwards. They diverge off to each side. However, the eye is normally angled to point directly forwards. This means that when the superior or inferior recti act on the eye, they are not only pulling it upwards or downwards, but they are also causing it to intort or extort and adduct.
Describe intorsion
The superior oblique muscle originates at the back of the eye but passes through a fibrous sling called the trochlea, which is located in the superior and medial corner of the orbit. The muscle then inserts onto the top of the eye, so it’s action will pull the top of the eye medially, causing it to rotate. The top of the eye rotating inwards is called intorsion.
Describe extorsion
The inferior oblique muscle originates from the medial orbital wall and inserts on the bottom of the eye. Its action will pull the bottom of the eye medially, also causing it to rotate, but in the opposite direction. With the top of the eye rotating outwards, this is called extorsion.
What is the reason the eye needs oblique muscles?
The reason that the eye needs the oblique muscles to be able to intort and extort is to counter the secondary effects of extorsion and intorsion caused by the inferior and superior recti muscles respectively. This helps maintain steady vision when looking up or down.
Outline the eye
The eye is responsible for providing us with sight. As light enters the eye, it is focused to converge onto the retina where it is detected by specialised cells (rods and cones). These cells generate nerve impulses which are transmitted along the optic nerve and optic tracts towards the primary visual cortex in the occipital lobe.
What is accommodation?
To achieve good vision, the eye must be able to focus light to varying amounts depending on how far away the object is that is being visualised
How does the eye achieve accommodation?
To achieve this, the eye adjusts the thickness of the lens within it. A thicker lens will cause greater refraction of light and is useful for looking at near objects. A thinner lens will cause less refraction of light and is useful for looking at distant objects.
What is the function of the ciliary muscles?
The ciliary muscles are responsible for adjusting the thickness of the lens. They are supplied by parasympathetic fibres that travel within the oculomotor nerve (CN III). Because of this, accommodation is an autonomic function that we are unable to control.
What happens when there is too much light?
To protect the retina from over-exposure to light, the eye must be able to limit how much light enters the eye. To achieve this, a circular muscle within the iris known as constrictor pupillae will constrict the pupil when too much light is detected on the retina.
What is the constrictor pupillae muscle supplied by?
This muscle is also supplied by parasympathetic fibres that travel within the oculomotor nerve (CN III). Because of this, pupillary construction is another autonomic function that we are unable to control.
What happens to the eye when it is dark?
Conversely, when it is dark, the eye must be able to allow more light in to allow us to see adequately. To achieve this, a radial muscle within the iris known as dilator pupillae will dilate the pupil when not enough light is detected on the retina
What innervates the dilator pupillae?
This muscle is supplied by sympathetic fibres that originate from the sympathetic chain and enter the skull alongside the internal carotid artery. Because of this, pupillary dilation is another autonomic function that we are unable to control.
What happens to the pupils when the parasympathetic or sympathetic nervous systems are activated?
When there is stimulation of the body’s parasympathetic or sympathetic nervous systems, the pupils may change size. For example, in states of fear, excitement or pleasure, the sympathetic nervous system is highly active, and the pupils will dilate. In states of resting, the parasympathetic nervous system is active, and pupils will constrict
Does the pupillary response override the effects of the symp/parasymp nervous systems?
Yes
What is the pupillary light reflex?
The pupillary light reflex, which is responsible for automatically adjusting the amount of light entering the eye, has an afferent (sensory) and efferent (motor) nerve
What is the pathway of an impulse when there is a change in light intensity?
The afferent nerve is the optic nerve, and it carries information about the amount of light being detected on the retina to the midbrain. Here, there is a synapse with the Edinger-Westphal nucleus, which instructs the efferent nerve (the oculomotor nerve) to initiate constriction of the constrictor pupillae muscle in the iris, thereby narrowing the pupil and reducing the amount of light entering the eye.
What is the direct pupillary response?
When a light is shone in one eye of a healthy patient, both pupils will constrict. The constriction of the pupil which is having a light shone into it is called the direct pupillary respons
What is the consensual pupillary response?
when the pupil that doesn’t have the light shining in it also contracts
Why does the consensual pupillary response occur?
The reason that the other pupil constricts as well is because there is a connection between the right and left Edinger-Westphal nuclei such that if one side is activated, then both sides are activated.
What does the lacrimal gland do?
The lacrimal gland produces tears to lubricate and moisten the surface of the eye. It is located in the superior and lateral corner of the orbit.
What is the pathway of tears from the lacrimal gland?
The tears flow across the eye and drain into the lacrimal ducts in the inferior and medial corner of the orbit. Through here, they then drain into the nasal cavity via the nasolacrimal duct. This is why our nose runs when we cry
What innervates the lacrimal gland?
The secretomotor nerve supply to the lacrimal gland is via the parasympathetic fibres within the facial nerve (CN VII).
Describe orbital wall fractures
Direct traumatic blows to the eye (as may be sustained during a fist fight) may fracture the walls of the orbit. These are known as ‘blow out’ fractures and a fracture of the inferior orbital wall is most common. The inferior rectus muscle can become trapped inside the fracture, tethering the eye in position and patients will be unable to look up.
What are cataracts?
A cataract is a common ocular condition characterised by clouding of the lens that is responsible for focusing light onto the retina. Cataracts develop slowly and painlessly, and whilst they cannot be prevented, they are relatively easily treated surgically, by removing the affected lens and replacing it with a new and clear intraocular lens.
What is oculomotor nerve palsy?
If the oculomotor nerve is not functioning on one side, it produces a very characteristic set of findings on clinical examination. The affected eye will rest in a ‘down-and-out’ position (depressed and abducted). This is because the lateral rectus and superior oblique muscles are unopposed so pull the eye into that position at rest. The affected eye’s pupil will also be dilated due to loss of parasympathetic nerve supply to the constrictor pupillae, leaving dilator pupillae unopposed. Finally, due to the loss of motor nerve supply to levator palpebrae superioris, the eyelid will droop. This is known as ptosis. Additionally, on asking the patient to look left and right, the affected side will be unable to adduct.
What is abducens nerve palsy?
If the abducens nerve is not functioning on one side, the affected eye will be unable to abduct as the lateral rectus muscle is no longer working. The lateral rectus muscle may be overpowered by the medial rectus, which is still functional, to pull the eye medially at rest causing strabismus (sometime referred to as a ‘squint’).
How do doctors use the eyes to test cranial nerves?
Testing the different movements of the eye is a vital part of a neurological examination of the cranial nerves. The do this, a clinician may ask the patient to follow their finger as they draw the shape of the letter ‘H’ in front of the patient. The clinician observes the patient’s eyes to ensure they are moving together and asks the patient if they are experiencing any diplopia (double vision).
How do drugs affect the pupillary response?
Certain therapeutic and recreational drugs will cause changes to the size of the pupil. Opiates, for example, such as morphine and heroin (diamorphine), will cause pupillary constriction in higher doses. Sympathomimetics, such as ecstasy (MDMA) and cocaine will cause pupillary dilation. The size of the pupil can help clinicians during assessment of unconscious patients.
How do head injuries affect the pupillary response?
If a patient suffers a significant head injury and has bleeding inside the skull (for example, an extradural haemorrhage), intracranial pressure will rise. This may lead to compression of the oculomotor nerve on one or both sides. If compressed, the oculomotor nerve may be unable to function properly and an early sign of this is dilation of the ipsilateral pupil. This is another reason why clinicians often check the size of a patient’s pupils during clinical examination of unconscious patients. A fixed and dilated pupil is a concerning sign.
Describe the outer ear
The most external part of the ear consists of the pinna (or ‘auricle’), the ear canal (or external acoustic meatus) and the tympanic membrane (eardrum). The pinna is shaped to gather sound waves and direct them into the ear canal. The ear canal directs these sound waves towards the tympanic membrane. When sounds waves strike the tympanic membrane, it vibrates like the surface of a drum and transmits them deeper into the ear towards the cochlea.
Outline the middle ear cavity
Immediately behind the tympanic membrane is the middle ear cavity. Within it, are the ossicles. The ossicles are three of the smallest bones in the body and they carry the sound waves to the oval window which conveys it into the cochlea.
What is the malleus?
The first ossicle rests against the tympanic membrane. It is shaped like a hammer, from which its name is derived. The handle of the ‘hammer’ rests against the tympanic membrane and can be seen through the membrane during otoscopy (looking in a patient’s ear). The head of the hammer connects to the incus.
What is the incus?
The second ossicle’s name means ‘anvil’. As the ‘hammer’ (malleus) strikes the ‘anvil’ (incus), sound waves are transmitted, eventually reaching the stapes.
What is the stapes?
The third and final ossicle’s name means ‘stirrup’, which it clearly resembles. It receives sound wave vibrations from the incus and transmits them onto the oval window which marks the boundary of the middle and inner ear cavities.
Where is the opening of the eustachian tube?
The superior opening of the auditory tube (also known as the Eustachian tube) is also located in the middle ear cavity.
Where is the inferior opening of the eustachian tube and what is the significance of this?
The inferior opening of the auditory tube is in the posterior and inferior part of the nasal cavity. It therefore provides a connection of airflow between the external environment and the middle ear cavity via the nasal cavity. This connection is vital to maintain equal air pressure on either side of the tympanic membrane.
What would happen if you didn’t have a eustachian tube?
Without it, air pressure would build up on the inside or outside of the tympanic membrane, causing pain and potentially rupture.
Why do your ears pop when you are on an aeroplane?
This pressure can be felt when descending in an aeroplane from a significant height, or when diving underwater. As you descend deeper, air (or water) pressure outside the tympanic membrane increases and causes the membrane to bulge inwards. To counter this, air is allowed to pass up through the auditory tube to increase air pressure on the inside of the tympanic membrane. Sometimes, if the pressure correction occurs suddenly, you can feel a ‘pop’ in your ear.
What ate the two muscles of the middle ear cavity and what do they do?
- Tensor tympani
- Stapedius
Act to dampen sound vibrations and reduce perceived volume.
What does the tensor tympani muscle do and what innervates it?
Inserts on the malleus and when it contracts, it increases tension in the tympanic membrane, reducing how much it can vibrate. Tensor tympani is supplied by the mandibular branch of the trigeminal nerve (CN V).
What does the stapedius muscle do and what innervates it?
The stapedius muscle inserts on the stapes and acts in similar way. When it contracts, it dampens the vibrations of the stapes. Stapedius is supplied by the facial nerve (CN VII)
What are the 4 key elements of the blood brain barrier?
- Endothelial cell tight junctions
- Lack of BM fenestrations
- Astrocytic end feet
- Pericytes
Most common stroke territory
Area supplied by middle cerebral artery as it is the closest to the internal carotid artery
What is collateral blood supply?
If you block off one artery the area can still be perfused by other smaller blood vessels
This is the case in the circle of Willis
What is a common site of atherosclerosis?
The bifurcation point of the common carotid artery
What are the anterior and posterior parts of the brain blood supply supplied by?
Anterior- internal carotid artery
Posterior- Vertebral artery
What is impacted first when there is a reduction in blood supply?
Watershed regions
In between the vascular territories
Where is the superior sagittal sinus?
Along the top of the brain in the falx cerebri
Vasculature of spinal cord
anterior spinal vein and anterior spinal artery on anterior side
posterior spinal vein, posterior spinal arteries and posterolateral spinal veins on the posterior side
What are the parts of the ventricular system?
Lateral ventricles (I&II)
Interventricular foramen
3rd ventricle
Cerebral aqueduct
4th ventricle
foramen magandie
What are ventricles lined by?
Ependymal cells- glial cells
Look like epithelial cells
Cillia to beat and move CSF
What generates csf?
Choroid plexus- highly vascularised
Describe interstitial fluid drainage
Interstitial fluid drains → CSF via perivascular channels.
CSF drains via
arachnoid granulations
peripheral nerves to lymphatics
Importantly: nasal mucosa lymphatics → deep cervical lymph nodes
What do lymphnodes in neck do?
Lymphoid immune surveillance
Assessing for infection in brain
Olfactory nerve (CNI)
Sensory innervation of the nose
Optic nerve (CNII)
Sensory innervation of the eyes
Trochlear (CNIV)
Motor innervation of the superior oblique muscle
Oculomotor (CNIII)
Motor innervation of all eye muscles except lateral rectus and superior oblique
What is the only cranial nerve to come off the back of the brainstem?
Trochlear
What does the inferior olivary nucleus do?
Part of the olivo-cerebellar system and is mainly involved in cerebellar motor-learning and function.
What divides the pons and medulla?
Bulbopontine sulcus
Main connection between pons and medulla and the brain
Middle cerebellar peduncles
What is the rhomboid fossa?
Forms floor of the 4th ventricle
Dorsal columns
Carry joint position sense- position of limbs
Superior brachium
Back of midbrain
Visual sensory area
inferior brachium
Auditory sensory area
How do we divide the pons
Tectum- everything in front of the cerebral aqueduct
Tegmentum- everything behind the cerebral aqueduct
Substrantua nigra
Initiates movement
contains neuromelanin
Parkinsons damages this
What are the cerebellum divisions?
Archicerebellum
Paleocerebellum
Neo cerebellum
What does the arachicerebellum
Floculonodular lobe:
balance. Connected to vesibular nuclei and reticular nuclei.
What is the paleocerebellum?
Muscle tone and posture
Afferent: dorsal spinocerebellar tracts via inf cerebellar peduncle and ventral SC tract via superior CP
Efferent: Globose and emboliform nuclei to red nucleus to rubrospinal tract
Neo cerebellum
(more fancy movements, coordination, muscle tone)
Afferent: Cerebral cortex to pontocerebellar fibres (decussate) via MCP
Efferent: Purks to dentate to red nucleus & ventral thalamus via SCP
Describe cerebellar wiring
Mossy fibres from cortex (ponto cerebellar pathway), vestibular nucleus, spinal cord, reticular formation, deep cerebellar nuclei (feedback)
Fornix
Major output pathway of the hippocampus
Limbic system and the papez circuit
Hippocampus
Laying down memory
Lose the ability to make new memories if removed
Diencephalon
Deep grey structures
contains internal capsule- white streak
Describe the thalamus
3 main groups of nuclei:
sensory relays
cerebellar and basal ganglia relays to motor frontal lobe
connected to associative and limbic areas of cerebral cortex
Damage causes loss of sensation, pain, or movement disorders
Thalamic connections
Basal ganglia
Deep grey structures that aren’t the thalamus
Main inputs to the hypothalamus
Hippocampus
Amygdala
Circulating blood
Main outputs of the hypothalamus
Pituitary -> hormones -> homeostasis
singulate gyrus
Part of limbic system
Where does the spinal cord end?
Around L1
Means you can take some csf from there without damaging spinal cord
Coverings of spinal cord
Same as the rest of the brain
Dura mater- aka thika
Arachnoid
Pia
Dorsal horns
sensory info
fewer neuronal cell bodies
Dorsal root
Ventral root
Dorsal root ganglion
Anterolateral cordotomy
Now usually done percutaneously
For treatment of intractable pain.
Side effects include sleep apnoea due to reticulospinal tract damage
Spinothalamic tract
Crude touch,
Pain
Temperature
cross then up
Dorsal column-medial lemniscus
pathway
Vibration
Joint position
up then cross
Corticospinal (pyramidal) tract
Movement
brown sicard syndroma
What are dorsal and ventral roots associated with?
Dorsal root -> afferent (affected by the world- sensory)
Ventral root -> efferent (having an effect on the world- motor)
What is the medulla involved in?
Contain caudal part of the reticular
formation (“little net”):
low level sensorimotor control –
e.g. balance
Involved in variety of vital functions: Sleep/Wakefulness Motor Plant: movement, maintenance of muscle tone Various cardiac, circulatory, respiratory, excretory reflexes Contains tracts carrying signals between the rest of the brain and the body.
What do the pons do?
Relay from cortex and
midbrain to the cerebellum
Contains millions of neuronal
fibers
Pontine reticular formation (pattern generators) – e.g. for walking
What does the cerebellum do?
Smaller than the brain but contains as many neurons as all the rest of the CNS.
“Motor errors” between intended movement and actual movement – adjusts synaptic weights to eliminate error.
Online correction can take place during the movement : motor learning.
Thought exclusive for motor coordin-ation – recently implicated in cognitive and affective/emotional function.
COmponents of the midbrain
Tegmentum and tectum
What does the tectum do?
Visual/spatial and auditory frequency maps
What are the two parts of the tectum?
Superior colliculus- Sensitive to sensory change – orienting/defensive movements
Inferior colliculus- similar but for auditory events
What are the 3 structures of the tegmentum?
Periaqueductal grey
Red nucleus
Substantia nigra
WHat does the periaqueductal grey do
Role in pain (ascending and descending signals)
Role in defensive behavior
Role in reproduction
What does the red nucleus do?
Role in pre-cortical motor
control
(especially arms and legs
Target of cortex and cerebellum, projects
to spinal cord
What does the substantia nigra do?
Substantia nigra pars reticulata –
basal ganglia output
Substantia nigra pars compacta
(Dopamine cells) – basal ganglia
Input…Parkinson’s disease
Describe the parts of the thalamus and what it generally does
Relay structure
Specific nuclei : relay signals to cortex/limbic system for all sensations (but smell…).
Non-specific nuclei : Role in regulating state of sleep and wakefulness and levels of arousal
Important relays from basal ganglia and cerebellum back to cortex
What does the hypothalamus do?
Regulates the pituitary gland which regulates hormonal secretion: interface between brain and hormones
Role in hormonal control
of motivated behavior
…including hunger, thirst, temperature, pain, pleasure and sex
WHat are the subcortical portions of the cerebral cortex
Basal Ganglia
Limbic system
What is the basal ganglia for?
Group of structures
Loop organization
These structures thought to be involved in motor function since involved in movement disorders
However: work in Sheffield has been key to newer understanding of fundamental roles in action selection and reinforcement learning
What does the limbic system do
Group of structures
These structures involved in emotion, motivation and emotional association with memory
The limbic system influences the formation of memory by integrating emotional states with stored memories of physical sensations
What makes up the cortical lobes?
White matter: fibers / axons
Gray matter (6 layers) : cell bodies
What does the frontal lobe contain?
Contain the precentral gyrus from which motor instructions (particularly for fine motor control) that are sent to muscles controlling hands and feet.
Primary motor cortex: contains many of the cells giving origin to the descending motor pathways - it is involved in the initiation of voluntary movements.
Premotor and supplementary motor areas: higher level motor plans and initiation of voluntary movements.
What is the frontal lobe involved in?
Involved in - i.e. lesions disrupt….
“Executive” planning – generating models of the consequences of actions
Judgmental roles
Emotional modulation
Working memory: short-term information (rather than long-term factual data)
Control of behavior that depends upon context or setting
Prefrontal cortex: generating sophisticated behavioural options that are mindful of consequences
What does the cochlear do?
As sound waves and vibrations travel through fluid within the cochlea, they are converted into electrical impulses which are passed via the cochlear nerve to the auditory cortex. This allows us to perceive sound
How does the cochlear work?
The sound waves first enter the cochlea via the oval window (which the stapes is in contact with). The round window is located nearby and bulges in and out to allow the fluid within the cochlea to move.
What is the vestibular system made up of?
Consists of the semicircular canals, utricle and saccule. The vestibular system contains fluid, which flows when we move our heads
How does the vestibular system work?
The movement of this fluid is detected by specialised cells causing them to produce electrical impulses. These impulses are passed along the vestibular nerve towards various parts of the brain including the cerebellum, thalamus and certain cranial nerve nuclei
What do the three semi-circular canals do?
The three semicircular canals, positioned perpendicular to each other in three dimensions, allow us to perceive movement.
What does the utricle and saccule do?
Perceive linear acceleration
What carries the impulses from the cochlear to the pons?
Impulses from the cochlea and vestibular system are carried by the vestibulocochlear nerve (CN VIII), through the internal auditory meatus towards the nuclei of the vestibulocochlear nerve in the pons.
What is the oculocephalic reflex?
In the nuclei of the vestibulocochlear nerve there are connections to other brainstem nuclei of the oculomotor, trochlear and abducens nerves which control eye movements. Because of these connections, we are able to maintain fixed gaze whilst moving our head. This is called the oculocephalic reflex.
Vertigo
Vertigo is the symptom of being able to perceive movement when there is none. This is commonly perceived and recreated if you spin around several times and then stop suddenly. The perception of the world continuing to spin around you, or the floor moving unevenly beneath you, is vertigo. There are various causes of vertigo, but a common presentation to clinical practice is a disorder of the vestibular system. Inflammation, infections, endo/perilymph disorders or cancers of the vestibular system or nerves may cause vertigo.
Vestibular schwannoma
Also known as an acoustic neuroma, this is a benign tumour of the Schwann cells surrounding the vestibulocochlear nerve. As it grows, it gradually leads to symptoms of unilateral hearing loss, tinnitus, a feeling of fullness in the ear and vertigo. If it grows large enough, it will start to compress the other cranial nerves that leave the brainstem around the same position. This position is known as the cerebellopontine angle, and other cranial nerves leaving the brainstem here are the trigeminal (CN V) and facial (CN VII) nerves.
Otis media
Otitis media is the term for inflammation within the middle ear cavity. It is most often caused by a simple viral infection and is particularly common in young children. When a patient is suffering from an upper respiratory tract infection, the inflammation can spread throughout the upper respiratory tract from the nose and pharynx to the middle ear cavity via the auditory tube. This can lead to accumulation of inflammatory fluid and pus in the middle ear cavity, impairing conduction of sound waves along the ossicles.
Otis media in children
The auditory tube is relatively narrow in young children and therefore less effective at draining the middle ear cavity. Because of this, a build of pus behind the tympanic membrane can increase pressure significantly which can be painful. If the inflammation continues, the tympanic membrane may rupture due to the pressure. This may relieve the pain and allow drainage of the pus. The tympanic membrane will usually later heal on its own. However, more serious cases of otitis media can spread deeper into the ear and cause inflammation of the cochlea or vestibular system, mastoid process of the temporal bone or the meninges.
What are Brodmann’s areas?
Frontal gyri
Temporal gyri
singulate gyrus
continues around the central sulcus
parahippocampal gyrus
Facial nerve (CN VII)
Motor innervation of the muscles of the face
Vestibulocochlear (CN VIII)
Sensory innervation of the inner ear
Trigeminal (CN V1, V2, V3)
Sensory innervation of face, sinuses, teeth ect
Motor innervation of muscles of mastication
Abducens (CN VI)
Motor innervation of the lateral rectus muscle
Facial nerve (CN VII)
Motor innervation of the muscles of the face
Glossopharyngeal (CN IX)
Motor innervation of the pharyngeal musculature
Sensory innervation of posterior 1/3 of tongue, tonsils and pharynx
Vagus nerve (CN X)
Motor innervation of heart, lungs, bronchi and gi tract
Sensory innervation of the heart, lungs, bronchi, trachea, pharynx, larynx, GI tract, ext ear
Spinal accessory nerve ( CN XI)
Motor innervation of sternocleidomastoid and trapezius muscles
Hypoglossal nerve (CN XII)
Sensory innervation of muscles of the tongue
Immediate nerve
Motor innervation of the submandibular and sublingual glands
Sensory innervation of the anterior 2/3rds of the tongue
What are the 3 layers of the eye?
Outer layer- sclera and cornea
Middle layer- uvea
Inner layer- retina
What forms the cornea?
The sclera
Sclera
Cartilage
protects eye
Cornea
Made of collagen- it is a barrier to trauma and infection
It has to be transparent for light transmission
It is responsible for 2/3 refractive power of the eye
What are the 5 layers of the cornea?
Epithelium- can regenerate
Bowman’s layer
Stroma
Descemet’s layer
Endothelium- cannot regenerate
Middle layer
Made up of iris, ciliary body and choroid
What is a ciliary body?
Glandular epithelium produces aqueous humour
Ciliary (smooth muscle) controls accommodation
Describe the inner layer
Made up of:
- Retina
- Specialised organ of phototransduction
- Many layers
What is the anterior chamber?
Neurons and receptors in the retina
Ganglion cells
Bipolar neurons
Rod cells
Cone cells
Key parts of the retina
Macula lutea- centre of the retina
Fovea centralis- centre of the macula lutea
Cones
Rods
Optic nerve
Made up of axons of ganglion cells
Where is the midbrain and what are its two parts?
The midbrain sits at the very top of the brainstem and is often difficult to see on an undissected specimen. The optic chiasm obstructs most of the view of the anterior brainstem. It is divided broadly into two parts, one ventral (tegmentum) and one dorsal (tectum) to the cerebral aqueduct
Describe the tectum
this smaller part of the midbrain is located dorsally. It contains two pairs of rounded bumps, known as colliculi.
What do the superior colliculi do?
Involved in regulating eye movements and reflexes associated with visual stimuli, such as turning or moving the head quickly when something quickly enters our field of vision.
What do the inferior colliculi do?
Involved sound location, pitch discrimination and reflexes associated with auditory stimuli, such as turning our head on hearing a loud noise.
Describe the tegmentum
This larger part of the midbrain is located ventrally. It contains the substantia nigra, cerebral peduncles and red nuclei
What dies the substantia nigra do?
Important in motor control by producing dopamine.
What are the cerebral peduncles?
On its most ventral surface which are large white matter bundles that connect the midbrain to the thalami,
What do the red nuclei do?
Which are involved in supporting motor control of the limbs.
What nuclei does the midbrain contain?
The midbrain contains the nuclei of the oculomotor (CN III) and trochlear (CN IV) nerves, and the Edinger-Westphal nuclei (involved in the pupillary light reflex).
What is the pons and what does it contain?
The pons is the large, rounded, middle part of the brainstem. On its ventral surface lies the basilar artery and on its dorsal surface, it has large white matter connections to the cerebellum called the middle cerebellar peduncles. The fourth ventricle of the ventricular system is situated dorsal to the pons, between the two middle cerebellar peduncles
What nuclei are in the pons?
The pons contains the nuclei of the trigeminal (CN V), abducens (CN VI), facial (CN VII) and vestibulocochlear (CN VIII) nerves. It also contains the pneumotaxic and apneustic centres which are involved in the regulation of breathing
Describe the medulla
The medulla oblongata connects the pons to the spinal cord. It has a groove on its ventral surface known as the anterior median fissure. The medulla contains the two medullary pyramids, which form two distinct lumps of the ventral surface, separated by this fissure. Essential motor tracts known as the corticospinal tracts run inside the pyramids. Immediately lateral to the medullary pyramids are another pair of prominent ridges known as the medullary olives.
What is the dorsal column medial lemniscus?
An important sensory pathway of nerves runs in the dorsal part of the medulla within two pairs of nerve bundles: fasciculus gracilis and fasciculus cuneatus. Fibres of both corticospinal and DCML tracts cross over to the contralateral side within the medulla
Describe the nuclei of the medulla
The medulla contains the nuclei of the glossopharyngeal (CN IX), vagus (CN X), accessory (CN XI) and hypoglossal (CN XII) nerves. The medulla also contains vital centres responsible for regulating respiration, heart rate and blood pressure, and initiating vomiting
What is bulbar palsy
This term refers to dysfunction of the cranial nerves that arise from the medulla (glossopharyngeal, vagus, accessory and hypoglossal). Symptoms include difficulty speaking and swallowing, excessive saliva production, wasting and fasciculations of the tongue and an absent gag reflex. Causes include diseases which affect peripheral nerves such as motor neurone disease and Guillain-Barré syndrome.
What are the cranial nerves?
The cranial nerves are 12 pairs of named nerves that originate directly from the brain, instead of the spinal cord like other nerves. Each pair has its own function and leaves the skull via specific foramina. Understanding the individual characteristics of each pair of cranial nerves is important when testing them during a clinical examination.
Give an overview of the olfactory nerve
Specialised nerve cells in the roof of the nasal cavity detect odour molecules and convey this information superiorly through the cribriform plate to the olfactory bulbs. The olfactory bulbs are located on the superior surface of the cribriform plate, either side of the crista galli. The olfactory tracts then carry smell information posteriorly along the underside of the frontal lobes towards the olfactory cortices in the temporal lobes.
Give an overview of the optic nerve
The optic nerve carries sight information from the retina to the optic chiasm, where some fibres cross over
Give an overview of the oculomotor, trochlear and abducens nerves (CN III, IV, VI)
These nerves control the muscles that are responsible for movements of the eyes and diameter of the pupils
Give an overview of the trigeminal nerve
The trigeminal nerve is the largest cranial nerve and divides into three branches shortly after it exits the pons. The branches are often named V1, V2, and V3.
Describe the opthalmic nerve
A purely sensory nerve that supplies the skin over the superior third of the face as far as the top of the of the head, and the anterior surface of the eye
Describe the maxillary nerve
Also a purely sensory nerve that supplies the middle third of the face, including most of the internal nasal cavity, upper teeth and palate.
Describe the mandibular nerve
A mixed motor and sensory nerve. The sensory fibres supply the inferior third of the face, including general sensation to the anterior 2/3 of the tongue, and the mandibular teeth and gums. The motor fibres of the mandibular nerve supply five muscles.
What muscles are supplied by the mandibular nerve?
One is the tensor tympani in the middle ear and the other four are the ‘muscles of mastication’ which are responsible for moving our mandible to chew our food:
o Temporalis
o Masseter
o Medial pterygoid
o Lateral pterygoid.
Outline the olfactory nerve
Sensory
CNS origin- Cerebrum
Skull base foramen- Cribriform plate
Function- Olfaction (smell)
Outline the optic nerve
Sensory
CNS origin- Diencephalon
Skull base foramen- Optic canal
Function- Sight
Outline the oculomotor nerve
Motor (+ parasympathetics)
CNS origin- Midbrain
Skull base foramen- Superior orbital fissure
Function- Eye movements (SR, IR, MR, IO), eyelid opening (LPS), pupillary constriction and accommodation
Outline the trigeminal nerve
Sensory and motor
CNS origin- Pons
Skull base foramen- V1- Ophthalmic superior orbital fissure, V2- Maxillary foramen rotundum, V3- mandibular foramen ovale
Function- V1 – sensation from the upper third of face.
V2 – sensation from the middle third of face.
V3 – sensation from the lower third of face, motor to the muscles of mastication, motor to the tensor tympani muscle
Describe the abducens nerve
Motor
CNS origin- Pons
Skull base foramen- Superior orbital fissure
Function- Eye movements (LR)
Describe the start of the facial nerve
The facial nerve takes an unusual route out of the skull. It first passes through the internal auditory meatus alongside the vestibulocochlear nerve (CN VIII). Shortly after this, it gives off a branch which supplies parasympathetic secretomotor function to the lacrimal gland.
Describe the chorda tympani
As it progresses through the middle ear cavity, the facial nerve gives off a branch to the stapedius muscle and another branch known as the ‘chorda tympani’. This nerve supplies taste sensation to the anterior 2/3 of the tongue and parasympathetic secretomotor function to the submandibular and sublingual salivary glands
Where does the facial nerve exit the skull?
The facial nerve then leaves the temporal bone of the skull via the stylomastoid foramen which is located between the styloid and mastoid processes of the temporal bone, hence the name.
What happens to the facial nerve after exiting the skull?
After exiting the skull, it gives of a small branch which carries sensory information from the ear and motor supply to some muscles of the scalp. The main body of the facial nerve then enters the substance of the parotid salivary gland (which it does not innervate), and within it, divides into five branches which spread out across the face to supply the muscles of facial expression.
What are the 5 branches of the facial nerve?
Temporal, zygomatic, buccal, marginal mandibular and cervical branches.
Outline the facial nerve
Both (+parasympathetic)
CNS origin- Pons
Skull base foramen- Internal auditory meatus then stylomastoid foramen
Function- Motor to the muscles of facial expression, motor to the stapedius muscle, sensation from the ear canal, secretomotor function to the submandibular and sublingual salivary glands and lacrimal gland, taste from the anterior 2/3 of the tongue.
Outline the vestibulocochlear nerve
Sensory
CNS origin- Pons
Skull base foramen- Internal auditory meatus
Function- Balance and hearing
Outline the glossopharyngeal nerve
Sensory and motor (+ parasympathetics)
CNS origin- medulla
Skull base foramen- Jugular foramen
Function- Motor to the stylopharyngeus muscle, sensation from the pharynx and posterior 1/3 of the tongue, sensation from the carotid baroreceptors, secretomotor function to the parotid salivary gland, taste from the posterior 1/3 of the tongue.
Outline the vagus nerve
Sensory and motor (+ parasympathetic)
CNS origin- Medulla
Skull base foramen- jugular foramen
Function- Motor to the muscles of the soft palate, pharyngeal muscles and internal laryngeal muscles, sensation from the external ear and ear canal, taste from the epiglottis and parasympathetics to the thoracic and abdominal organs.
Outline the accessory nerve
Motor
CNS origin- Spinal cord C1-5
Skull base foramen- Foramen magnum (in) and jugular foramen (out)
Function- Motor to the trapezius and sternocleidomastoid muscles
Outline the hypoglossal nerve
Motor
CNS outline- medulla
Skull base foramen- hypoglossal canal
Function- Motor to the muscles of the tongue
What does the vestibulocochlear nerve do?
This purely sensory nerve carries information of the special senses hearing and equilibrium (balance) from the inner ear.
What does the glossopharyngeal nerve do?
The glossopharyngeal nerve has numerous functions. It supplies motor function to one muscle, the stylopharyngeus, which assists with facilitating swallowing. It carries general sensation from the middle ear, auditory tube, majority of the pharynx and both general and taste sensation from the posterior 1/3 of the tongue. It provides parasympathetic secretomotor supply to the parotid salivary gland and finally, it carries unconscious sensory information from the carotid chemoreceptors and baroreceptors towards the medulla.
What does the vagus nerve do?
Some of the main functions of this nerve have been discussed in previous modules (parasympathetic supply to thoracic and abdominal organs, and motor and sensory innervation to the larynx). However, it also supplies motor innervation to the muscles of the soft palate, palatine folds and pharyngeal constrictors, and carries general sensation from the ear canal and pinna. Finally, it carries taste sensation from the epiglottis of the larynx.
What does the accessory nerve do?
This purely motor nerve follows an unusual route. It does not actually originate from the brain. Its fibres originate from the spinal cord levels C1-C5. They join each other to form the spinal accessory nerve and enter the skull through the foramen magnum, then leave the skull again via the jugular foramen. The accessory nerve only supplies two muscles: sternocleidomastoid which is responsible for turning the head and nodding, and trapezius which is a large muscle on the back of the torso responsible for shrugging and numerus movements of the scapula.
What does the hypoglossal nerve do?
Finally, the hypoglossal nerve is a purely motor nerve. It leaves the skull as the only structure to pass through its named foramen, the hypoglossal canal, and supplies motor innervation to all intrinsic and extrinsic muscles of the tongue (except palatoglossus which is supplied by the vagus nerve). Damage to a unilateral hypoglossal nerve will cause that side of the tongue to be paralysed and atrophy, meaning the other side will overpower it. This leads to a characteristic finding of the tongue pointing towards the side of the lesion.
How to test olfactory nerve?
the clinician can simply ask the patient if their sense of smell has changed, or they can ensure the patient is able to identify certain strong-smelling compounds, such as coffee, chocolate, vanilla, or cinnamon.
How to test the optic nerve?
This nerve is tested in several ways. Firstly, visual acuity is tested using a Snellen chart (a chart with letters of decreasing sizes). Visual fields (peripheral vision), accommodation to near and far objects, colour vision, and the pupillary light reflex also test the optic nerve
How to test the oculomotor, trochlear and abducens nerve?
Tested by a clinician asking a patient to follow their finger as they move it across the patient’s field of vision. The clinician can observe the movements of the patient’s eyes to ensure they are moving as they should. The pupillary light reflex also tests the oculomotor nerve.
How to test the trigeminal nerve?
the motor and sensory parts of the trigeminal nerve are tested separately. Firstly, sensation is tested by simply ensuring the patient can feel a brush of cotton wool against their skin in the three regions of the face (forehead, cheek, jaw) on both sides. Sensation may be further tested by ensuring the patient is able to tell the difference between sharp and crude touch, or by testing the blink reflex when the cornea of the eye is touched. Motor function is tested by palpating a patient’s jaw muscles as they clench their teeth or asking the patient to forcibly open their mouth against resistance.
How to test the facial nerve?
The motor function of the facial nerve is its only function that is routinely tested. This is achieved by asking the patient to perform a series of facial movements, such a raising their eyebrows, closing their eyes tightly, blowing their cheeks out or showing all their teeth. The clinician looks for any asymmetry in their movements.
How to test the vestibulocochlear nerve?
the simplest way this nerve is tested is by blocking the one of the patient’s ears and whispering a number or word in the other ear and asking the patient to repeat it to check their hearing. The test is repeated with the other ear. The function of the ear, cochlear and vestibular system can be tested more thoroughly with other tests using tuning forks and dedicated equipment in specialist clinics.
How to test the glossopharyngeal nerve?
This nerve is tested by assessing the patient’s gag reflex. A tongue-depressor (a blunt wooden ‘lolly-stick’) is pressed against the oropharynx and a normal finding would be the patient ‘gagging’ or looking like they will vomit. This tests the sensory function of this nerve
How to test the vagus nerve?
There are several ways to test the vagus nerve. The gag reflex above tests the motor function of the vagus nerve, but it can be further tested by asking the patient to open their mouth and say ‘ahhh’. This should cause elevation of the soft palate by muscles which are supplied by the vagus nerve. Coughing and swallowing also both require function of the vagus nerve.
How to test the accessory nerve?
To test the trapezius muscle, a clinician can ask the patient to shrug their shoulders, and to test the sternocleidomastoid, a clinician asks the patient to turn their head against resistance.
How to test the hypoglossal nerve?
The hypoglossal nerve is tested by asking the patient to protrude their tongue. Deviation of the tongue to one side or the other may imply damage to one of the hypoglossal nerves
Basic overview of how the eye works
Light is detected by the retina within the eye and impulses are passed via the optic nerves, then optic tracts and finally the optic radiations before reaching the primary visual cortex in the occipital lobe. The fibres divide and cross over in a complex way
What are visual fields and what are the two types?
The areas of vision that we can see with each eye are known as the visual fields. Each visual field is divided into a temporal field and a nasal field.
Describe the temporal visual field
The temporal field is the lateral half of the visual field, the nasal retina provides our temporal visual field
Describe the nasal visual field
Nasal field is the medial half
The temporal retina provides our nasal visual field.
Describe the journey of visual info from the optic nerves to the optic chiasm
Visual information from the retinas first travels along the right and left optic nerves to the optic chiasm. This structure is located immediately anterior to the midbrain and superior to the pituitary gland. At the optic chiasm, visual information from the temporal visual fields (nasal retinas) from each eye cross over, such that information about the temporal vision from the left eye now travels through the right side of the brain, and vice versa.
Describe the journey of visual info from optic tracts to the optic radiations
After the optic chiasm, the visual information travels along the optic tracts. When the tracts reach the thalamus, the majority of fibres synapse in the lateral geniculate nucleus. After they synapse, the fibres carrying the visual information towards the primary visual cortex divide into a superior and inferior pathway on each side, known as optic radiations
What is the parietal radiation?
The superior optic radiation travels in the parietal lobe, and is therefore known as the parietal radiation
What is the temporal radiation?
The inferior optic radiation travels in the temporal lobe, and is known as the temporal radiation, also known as ‘Meyer’s loop’.
Why do people say we see upside down?
The visual information within the parietal radiations is that which is received in the superior aspects of the retinas, and therefore constitutes the inferior fields of vision. Conversely, the information in the temporal radiation is from the inferior retinas, which is therefore from the superior parts of our field of vision.
How do the Edinger-Westphal nucleus and superior colliculi relate to sight?
They both also receive input from the optic tracts at the point close to where the fibres synapse in the lateral geniculate nucleus of the thalamus.
Why do people get visual field defects
Because of how visual information is passed from the retinas to the primary visual cortex, damage to different parts of the pathway will cause a different area of the visual field to be lost
Describe monocular vision loss
This defect is caused by damage to an optic nerve, meaning all vision is lost from the ipsilateral eye.
Describe bitemporal hemianopia
This term means ‘both – temporal – half – vison loss’ and is caused by damage to the optic chiasm. The fibres that cross at the optic chiasm are carrying visual information from the nasal retinas, and therefore information about the temporal visual fields.
Describe homonymous hemiamopia
This term means ‘same – half – vision loss’ and is caused by damage to an optic tract, between the optic chiasm and the lateral geniculate nucleus. If the left optic tract is damaged, information from the left temporal retina and right nasal retina is lost, meaning the left nasal visual field and the right temporal visual field are lost. This would mean the patient has lost the right side of their vision in both eyes, so would be termed a right homonymous hemianopia.
Describe homonymous quadrantopia
This term means ‘same – quarter – vision loss’ and is caused by damage to either the parietal or temporal optic radiation between the lateral geniculate nucleus and the primary visual cortex. This is a more complex field loss than the homonymous hemianopia but follows similar principles. If the left parietal optic radiation is damaged, information from the left superior temporal retina and right superior nasal retina is lost, meaning the left inferior nasal visual field and the right inferior temporal visual field are lost. This would mean the patient has lost the bottom-right corner of their vision in both eyes, so would be termed a right inferior homonymous hemianopia.
Describe a pituitary tumour
A tumour of the pituitary gland may cause it to enlarge. As it sits immediately beneath the optic chiasm, it can enlarge enough to compress the optic chiasm. This will cause the characteristic bitemporal hemianopia.
CNS vs PNSD
- Only the brain and spinal cord are ‘central’ nervous system*. Everything else is ‘peripheral’.
- the olfactory and optic nerves (CN I and II) are considered extensions of the brain rather than specific ‘nerves’ so they are CNS structures.
Where is the cerebellum?
Cerebellum means ‘little brain’ and it sits immediately beneath the occipital lobe. The Cerebellum is also located immediately posterior to the brainstem
What is the tentorium cerebelli and what does it do?
Fold of dura that separates the cerebellum from the occipital lobe
What do the cerebellar peduncles do and how many pairs of them are there?
Connect the cerebellum to the brainstem
3 pairs
Where is the 4th ventricle?
The fourth ventricle is trapped in the space between the posterior pons and medulla (ventrally) and the cerebellum (dorsally).
How is the cerebellum similar to the cerebrum?
Like the cerebrum, the cerebellum is divided into separate lobes by fissures.
And like the cerebrum, the cerebellum has two hemispheres, a left and right
Cerebellum also has gyri
What lobes does the primary fissure divide?
The anterior lobe is found on the superior surface of the cerebellum and is divided from the larger posterior lobe by the primary fissure.
Where is the horizontal fissure in the cerebellum?
A horizontal fissure is present within the posterior lobe
Describe the flocculonodular (3rd) lobe
The third lobe, the flocculonodular lobe, is located most ventrally and is made of the flocculus and nodule. The flocculus is located beneath the cerebellar peduncles, and the nodule is found in the midline.
What divides the two hemispheres of the cerebellum?
They are divided by a midline structure called the vermis.
What makes cerebellar gyri different from cerebrum gyri?
The cerebellum also has gyri, like the cerebrum, but they are much smaller and called folia.
What are functional areas of the cerebellum?
The cerebellum has unique anatomical features and specific functions. Certain parts of the anatomy of the cerebellum correlate with certain functions and together, they are known as functional areas of the cerebellum. Each functional area sends and receives its fibres via a specific cerebellar peduncle.
Spinocerebellum
Anatomical part- Vermis
Primary input- Spinocerebellar tracts
Cerebellar peduncle- Superior and inferior
Function- Correction and modulation of fine movements
Cerebrocerebellum
Anatomical part- Lateral hemispheres
Primary input- Cerebral cortex
Cerebellar peduncle- Middle
Function- Planning of coordinated movements
Vestibulocerebellum
Anatomical part- Flocculonodular lobe
Primary input- Vestibular system (inner ear)
Cerebellar peduncle- Inferior
Function- Balance, posture, tone and stabilisation of eye movements
Which arteries supply blood to the cerebellum?
Superior cerebellar arteries (SCA)
Anterior inferior cerebellar arteries (AICA)
Posterior inferior cerebellar arteries (PICA)
(All also supply the brainstem)
Describe the superior cerebellar arteries
Branch from the most superior part of the basilar artery, just before it bifurcates into the posterior cerebral arteries.
Describe the Anterior inferior cerebellar arteries (AICA)
Branch from the most inferior part of the basilar artery, just after it is formed from the vertebral arteries.
Describe the Posterior inferior cerebellar arteries (PICA)
Branch from the vertebral arteries before they merge to form the basilar artery.
What is the acronym to remember the symptoms of disruption of cerebellar functions?
V-vertigo
A-ataxia
N-nystagmus
I-intention tremor
S-slurred speech
H-hypotonia
E-exaggerated past pointing
D-dysdiadochokinesia
Describe vertigo
As the cerebellum receives and processes a large amount of input from the vestibular system such as our sense of balance and the perception of movement, vertigo may be caused if it is damaged.
Describe ataxia
This term means poor coordination. Typically, it is obvious when observing a patient’s gait, as the patient may appear unstable, with a very wide step to try to stabilise themselves.
Describe nystagmus
This term refers to the subtle, rapid, backwards-and-forwards eye movements that can be observed when looking closely at a patient’s eyes at the extremes of their gaze. A small amount of horizontal nystagmus may be considered normal, but vertical or rotational nystagmus is almost always abnormal. There are other causes of nystagmus, but without a functioning cerebellum able to stabilise eye movements, patients may develop this symptom.
Describe intention tremor
Tremors are features of various neurological diseases and vary in character. In contrast to a Parkinson’s disease tremor, a tremor caused by a cerebellar lesion is absent at rest and appears as the patient ‘intends’ to do something, such as put their arms outstretched, or pick something up. This is because the cerebellum is unable to correct and modulate fine movements to stabilise the arm and hand.
Describe slurred speech
Coordination of fine movements is one of the functions of the cerebellum and this extends to the coordination of muscles involved in articulation of speech so cerebellar dysfunction may cause patients to have slurred speech
Describe hypotonia
Maintenance of tone and posture are functions of the vestibulocerebellum and therefore, cerebellar dysfunction will cause lack of tone
Describe exaggerated past-pointing
This is observed when asking a patient to touch their own nose, then reach out to touch the tip of your finger as you hold it in front of them. Rapid correctional movements are coordinated by the cerebellum to ensure their finger touches the target. Patients with cerebellar dysfunction are unable to correct their movements, so often ‘overshoot’ your fingertip when reaching for it and ‘point past’ it.
Describe dysdiadochokinesia
Often abbreviated to DDK, this symptom is demonstrated by asking a patient to rapidly alternate between touching the palmar and dorsal parts of their fingers onto the opposite palm. Patients with cerebellar dysfunction will struggle to coordinate this movement smoothly and will have difficulty rapidly pronating and supinating their forearms or will miss the palm entirely.
Describe the corpus callosum
The primary connection between the left and right hemispheres of the cerebrum. The corpus callosum is categorised as a group of commissural fibres (fibres that cross the commissure into the opposite cerebrum).
Describe the thalamus
A very important, central structure that acts as a relay for numerous functions of the brain including motor, sensory, visual, auditory, cognitive and emotional pathways.
Describe the hypothalamus
As its name would suggest, the hypothalamus sits immediately below the thalamus, and is key to homeostasis. It exerts control over numerous hormonal endocrine functions of the body and the autonomic nervous system
Describe the pituitary gland
Located at the end of a stalk known as the infundibulum, the pituitary gland secretes numerous important hormones, often under direction from the hypothalamus. The pituitary gland sits in the pituitary fossa (sella turcica) of the sphenoid bone, and the optic chiasm is immediately superior to it.
Describe the pineal gland
Considered to be part of the diencephalon but located immediately posterior to the colliculi of the midbrain, the pineal gland secretes melatonin. This hormone controls our sleep-wake cycle.
Describe the calcarine sulcus
Within this sulcus of the occipital lobe is the primary visual cortex.
Outline the limbic system
The limbic system is a group of deep brain structures that play a significant role in numerous important functions including learning, memory, and emotional control
What are the different parts of the limbic system?
Fornix, mamillary bodies, hippocampus, parahippocampal gyri, cingulate gyrus and cingulate sulcus, cingulum, sections of the olfactory and insular cortex, thalamus, hypothalamus, and nucleus accumbens and amygdala (discussed in the next section).
Describe the fornix
Similar in shape to the corpus callosum, but much smaller.
Describe the mamillary bodies
Small, round nuclei located at the anterior tip of the fornix.
Describe the hippocampus
Located immediately inferior to the inferior horn of each lateral ventricle, the hippocampi are part of the temporal lobes and are integral in converting short-term to long-term memory. It’s named is derived from its shape, which resembles a seahorse
Describe the parahippocampal gyri
As their name suggests, these gyri of the temporal cortices are located next to the hippocampi
Describe the cingulate gyrus and cingulate sulcus
This is a large gyrus and associated sulcus that is superior to it which are located immediately superior to the corpus callosum on both sides of the cerebrum.
What are the cingulum?
Fibres that travel from the cingulate gyrus to other parts of the limbic system, namely the parahippocampal gyrus, are called the cingulum. The cingulum is an example of a group of association fibres
What are association fibres?
Fibres that connect different parts of the same hemisphere
Describe amnesia
As the limbic system, and particularly the hippocampus, is responsible for formation of memory and conversion of short-term memory into long-term memory, a head injury or a disease which affects this area of the brain can cause amnesia. Amnesia can be classified into retrograde amnesia (meaning patients cannot recall events that took place prior to the onset of amnesia) or anterograde amnesia (meaning patients cannot create new memories after the onset but are able to recall long-term memories of things prior to the onset).
Outline the basal ganglia
The basal ganglia are a group of deep nuclei of the brain that contribute to the coordination, control and inhibition of motor function. There are five main named parts to the basal ganglia. There is a left and right nucleus for each part of the basal ganglia.
Where are the 5 parts of the basal ganglia?
They are spread throughout the cerebrum, diencephalon, and midbrain. They are located close to the thalamus. Very complex excitatory and inhibitory pathways exist between each nucleus of the basal ganglia,
Describe the caudate nucleus
A c-shaped structure that rest immediately medial to, and follows the curvature of, the lateral ventricle.
Describe the globus palliudus
A triangular-shaped nucleus that can be divided into an internal and external part.
Describe the putamen
An oval-shaped nucleus found immediately lateral to the globus pallidus.
Describe the substantia nigra
A black nucleus found in the midbrain. Notable for producing dopamine.
Describe the subthalamic nucleus
A small nucleus, located inferior to the thalamus, but superior to the substantia nigra.
What parts of the basal ganglia are grouped together bc of similarity in function?
- Lentiform nucleus – putamen and globus pallidus.
- Striatum – caudate nucleus and lentiform nucleus.
What additional structures are close to the basal ganglia and are anatomically part of it but not functionally?
Nucleus accumbens
Amygdala
Describe the nucleus accumbens
Located at the anterior junction between the caudate nucleus and putamen, this nucleus plays a role in reward systems and is a subject of research into addiction.
Describe the amygdala
A small, spherical nucleus at the tip of the inferior horn of the caudate nucleus. It is involved in memory and emotional responses such as fear and anxiety.
What is the internal capsule?
Amongst the basal ganglia, between the globus pallidus and thalamus, is a bundle of white matter tracts known as the internal capsule. This very important structure forms part of the route of the majority of sensory and motor axons travelling to and from the cortex.
What are the fibres in the internal capsule?
The fibres within the internal capsule are examples of projection fibres, as they connect the cortex to deeper structures
What happens when the internal capsule is damaged?
Damage to the internal capsule (for example, from a stroke) can cause significant contralateral motor and sensory dysfunction
What is the corona radiata?
The axons that pass from the internal capsule to the cortex form the corona radiata. These fibres are shaped such that they ‘radiate’ out of the internal capsule towards the cortex.
Describe parkinson’s disease
Parkinson’s disease is caused by degeneration of the dopamine-producing neurones of the substantia nigra. This leads to a reduction in the passage of impulses within the basal ganglia which impairs the initiation and inhibition of movement. The most characteristic symptom is a ‘pill-rolling’ resting tremor. Other symptoms include a shuffling gait with small steps which is difficult to initiate and difficult to stop, ‘cogwheel’ rigidity best seen in the upper limb muscles, micrographia (very small handwriting) and a ‘mask-like’ loss of facial expression. Dopamine can be replaced with an oral precursor drug called levodopa which can temporarily reduce the severity the symptoms.
What is the vertebral column?
The vertebral column, or ‘spine’ or ‘spinal column’ is a flexible column of bones running from the head to the pelvis.
What are the functions of the vertebral column?
- Protecting the spinal cord
- Supporting the head and torso
- Providing attachments for muscles and ribs
- Site of haematopoesis.
Describe the makeup of the vertebral column
It is made up of 33 vertebrae (singular: vertebra), although some of them are fused together:
* 7 cervical vertebrae which are found in the neck.
* 12 thoracic vertebrae which are found in the back of the thorax.
* 5 lumbar vertebrae which are found in the lower back.
* 5 sacral vertebrae which fuse to form the sacrum and are found in the pelvis.
* 4 coccygeal vertebrae which fuse to form the coccyx and are found in pelvis, caudal to the sacrum
How are the vertebrae named?
Individual vertebrae are named with a letter and a number. The letter represents its type (cervical, thoracic etc.) and the number represents its position within that type, from cranial to caudal. For example, the first cervical vertebra is called C1, followed by C2, C3, C4 etc. The first thoracic vertebra is called T1, followed by T2, T3 etc.
Describe the curves of the spine
The vertebral column has several distinct curvatures, referred to as a lordosis or a kyphosis. Lordosis is an ‘inwards’ curvature and kyphosis is an ‘outwards’ curvature.
* Cervical lordosis in the neck.
* Thoracic kyphosis in the upper back.
* Lumbar lordosis in the lower back.
Describe excessive curvature of the spine
Excessive lordosis or kyphosis may be caused by poor posture, muscle weakness, anatomical abnormalities, or injuries. A third type of curvature known as scoliosis is seen when the spine curves laterally. Scoliosis is not a normal feature of the spine.
Describe the body of the vertebrae
The large, often cylindrical, structure that is located most anteriorly. It supports the weight of the vertebral column above it. Neighbouring vertebral bodies are separated from each other by intervertebral discs.
Describe the pedicle of the vertebrae
This part stems posteriorly from the vertebral body and forms the lateral wall of the spinal canal.
Describe the lamina of the vertebrae
this part forms the posterior wall of the spinal canal. The spinous process stems from the lamina.
Describe the spinal canal
This is the hole formed by the body, pedicle and lamina. The spinal cord travels within the spinal canal.
Describe the transverse processes of the vertebrae
These are lateral protrusions from the vertebra at the junction between the pedicle and lamina that provide an attachment for muscles. In the cervical spine, they form a canal for the vertebral arteries. In the thoracic spine, they form the primary site of articulation for the ribs.
Describe the articular processes of the vertebrae
These are vertical protrusions from the vertebrae that provide a site of attachment to the vertebrae above and below. These synovial articulations are called facet joints.
Describe the intervertebral foramina
These holes at the side of each vertebra are formed by the spaces between the bodies and pedicles of neighbouring vertebrae. The spinal nerves leave the cord via these foramina.
Describe the atlas (C1) vertebrae
The atlas (C1) is the first cervical vertebrae and articulates directly with the occipital bone of the skull. This joint allows us to nod our heads. The atlas is shaped like a ring, and instead of having a vertebral body, the atlas bone has a space where it should be. It also does not have a spinous process.
Describe the axis (C2) vertebrae
The axis (C2) has a body that protrudes vertically upwards. This is called the odontoid process and is sometimes referred to as the ‘peg’ or ‘dens’. The odontoid process takes the place of the body of the atlas above it, such that the atlas can spin around the axis. This joint allows us to turn our heads and is called the atlanto-axial joint. It is an example of a pivot joint
Describe how C7 is different from C3-6
The other five cervical vertebrae are all similar in their shape but C7 has some slight differences. Cervical vertebrae have a smaller body than the other types as they support less weight. Their transverse processes have a hole in them – the transverse foramina – which transmits the vertebral arteries (except in C7) and they all have a bifid spinous process (meaning ‘two-pronged’) (except in C7). The spinous process of C7 much more prominent and is usually the most superior spinous process that you can palpate through the skin. For this reason, C7 is sometimes referred to as ‘vertebra prominens’.
Describe the thoracic vertebrae
The 12 thoracic vertebrae are all similar in shape and become increasingly larger from superior to inferior, as the most inferior vertebrae must support more weight. The thoracic vertebrae are unique from the other types as they have additional articular surfaces for the ribs. The spinous processes are long, sharp and point downwards, allowing them to protect the spinal canal more effectively.
Describe the lumbar vertebrae
The five lumbar vertebrae are the largest individual vertebrae in the spine. They support more weight than thoracic vertebrae so have very large vertebral bodies. Their transverse processes project laterally and provide an attachment for additional muscles. The spinous processes are large and, in comparison to the thoracic vertebrae, they are relatively short and rectangular.
Describe the sacrum and coccyx
The five sacral vertebrae are fused to form the sacrum, a large triangular-shaped bone that is located in the centre of posterior part of the pelvis. It articulates with the pelvis at the sacroiliac joints. There is an anterior prominence at the top of the sacrum called the sacral promontory. The four coccygeal bones are also all fused into one bone, the coccyx, which attaches to the inferior aspect of the sacrum.
Outline the features of the Atlas (C1) vertebrae
Vertebral body- Absent
Spinous process- Absent
Transverse processes- Transverse foramen
Primary movements- Rotation at atlanto-axial joint
Outline the axis (C2) vertebrae
Vertebral body- Elongated vertically as the ‘odontoid process’
Spinous process- Bifid
Transverse processes- Contains a transverse foramen
Primary movements- Rotation at atlanto-axial joint
Outline the features of the cervical (C3-7) vertebrae
Vertebral body- Small
Spinous process- Bifid (except C7)
Transverse processes- contains a transverse foramen
Primary movements- Flexion, extension and lateral flexion
Outline the features of the thoracic vertebrae
Vertebral body- Medium sized and heart shaped
Spinous process- Long, sharp and down-sloping
Transverse processes- contain articulations for ribs
Primary movements- Rotation
Outline the features of the lumbar (L1-5) vertebrae
Vertebral body- very large
Spinous process- Large, relatively short and rectangular
Transverse processes- long, flat and directed laterally
Primary movements- Flexion, extension and lateral flexion
Outline the features of the sacral (s1-5) vertebrae
Vertebral body- Fused
Spinous process- Fused
Transverse processes- None
Primary movements- None
Outline the features of the Coccygeal (Co1-Co4) vertebrae
Vertebral body- Fused
Spinous process- Fused
Transverse processes- None
Primary movements- None
What are intervertebral disks?
Between the non-fused vertebrae of the spine are the intervertebral discs which are strong fibrocartilaginous structures able to withstand compression forces whilst also allowing flexibility and movement between each vertebra.
What are intervertebral disks made of?
They are made of a central gelatinous core called the nucleus pulposus. Surrounding the nucleus pulposus is the annulus fibrosus which is made of concentric rings of collagen.
Why is the joint between the intervertebral dics and the vertebral bodies a secondary cartilaginous joint?
The intervertebral discs are separated from the vertebral bodies of the neighbouring vertebrae by a thin layer of hyaline cartilage on the surface of the vertebral bodies above and below. This joint structure of ‘bone – hyaline cartilage – fibrocartilage – hyaline cartilage – bone’ is an example of a secondary cartilaginous joint.
What do the spinal ligaments called and what do they do?
The vertebral column is supported by several ligaments that help maintain upright posture and prevent hyperflexion and hyperextension injuries. They are the Anterior longitudinal ligament; Posterior longitudinal ligament; ligamentum flavum; Interspinous ligament; Supraspinous ligament
Where is the anterior longitudinal ligament?
Along the anterior surfaces of the vertebral bodies.
Where is the posterior longitudinal ligament?
Along the posterior surfaces of the vertebral bodies, but anterior to the spinal canal.
Where is the ligamentum flavum?
Along the inside of the laminae. ‘Flavum’ is Latin for ‘yellow’ and this ligament appears yellow due to amount of the elastin protein within it
Where is the interspinous ligament?
Between the spinous processes
Where is the supraspinous ligament?
Along the very tips of the spinous processes.
Describe the paraspinal muscles
The muscles that support the vertebral column are numerous. A group of these muscles are together known as the erector spinae. These muscles form a column either side of the spinous processes. They contribute to maintaining an upright posture and can often be palpated either side of the lumbar spine whilst standing.
Outline disk herniation
Disc herniation
Repetitive compression of the intervertebral discs can lead to weakening of the annulus fibrosus and posterior herniation of the nucleus pulposus which can narrow the intervertebral foramina or spinal canal. If an intervertebral foramen is narrowed and the transiting spinal nerve is compressed, this can cause weakness in muscles supplied by that nerve or altered sensation in the dermatome. If the spinal cord or cauda equina is compressed by the herniated disc, this can cause significant neurological deficit below that level and is a surgical emergency.
What is a lumbar puncture?
This procedure involves sampling some CSF from the subarachnoid space in the lower vertebral canal. As the spinal cord terminates at L1/L2, a lumbar puncture (LP) must be performed lower than L2 to avoid damaging the cord. Below this level, the nerves of the cauda equina are simply pushed out of the way of the needle rather than being damaged by it.
How do you find an appropriate space for a lumbar puncture?
To find an appropriate space between the vertebrae, the patient is positioned either sitting on the edge of a bed, or in the foetal position, and asked to push out their lower back to widen the space between the vertebrae. The L4/L5 space is in line with the intercristal plane (top of the iliac crests) so this is an appropriate space to aim for. As the needle reaches the subarachnoid space, the clinician can usually feel several gentle ‘pops’ when the needle pushes through the ligamentum flavum and dura mater. When CSF starts flowing out, the needle is in far enough.
Outline the use of anaesthetics in a similar way to lumbar puncture
Anaesthetic drugs may also be injected into the subarachnoid space through the same approach to give anaesthesia for surgery of the lower pelvis or lower limbs. This is known as spinal anaesthesia. A similar method involves injecting anaesthetic into the extradural space in the lower back and this is known as an ‘epidural’ anaesthetic.
Outlines the spinal nerves
At almost every vertebral level, a pair of spinal nerves leave the vertebral column via the intervertebral foramina (one on each side). Each pair of spinal nerves are named according to the vertebral level at which they leave the spine. For example, the spinal nerves that leave the spine at the level of the T4 vertebra are called the T4 spinal nerves.
Where do the spinal nerves leave the spine?
In the cervical spine, the spinal nerves leave the spine directly above their corresponding vertebrae, as far as C7. There is an additional pair of spinal nerves that leave the vertebral column below the C7 vertebra, and these are called the C8 spinal nerves (note, there is no C8 vertebra).
How many pairs of spinal nerves are there and where do they mostly leave the spine?
After the C8 spinal nerves, all remaining spinal nerves leave the vertebral column directly below their corresponding vertebra. Finally, there is only one pair of coccygeal spinal nerves (Co1), so in total there are 31 pairs of spinal nerves.
Describe the end of the spinal cord
At the level of approximately the L1-L2 junction, the spinal cord tapers off into a cone shape (called the conus medullaris) and terminates. The dura and arachnoid meninges continue down to the sacrum.
What happens to the pia mater after the cord terminates?
The pia mater thickens after the cord terminates to form a thin strand of fibrous tissue known as the filum terminale. This continues all the way to the coccyx where it helps tether the spinal cord in position.
Describe the cauda equina
Shortly before the cord terminates, it gives off all of its remaining spinal nerves that are yet to leave (L3-L5, S1-S5 and Co1) and these spinal nerves descend within the spinal canal until it is their designated level to the leave the vertebral column. This mass of spinal nerves dangling within the spinal canal resembles a horse’s tail and hence it is called the cauda equina, which means horse’s tail in Latin.
What are the two roots of the spinal nerves?
Each spinal nerve is formed of two roots that directly stem from the dorsal and ventral aspects of the spinal cord and are therefore named the dorsal and ventral roots.
Outline the dorsal root
The dorsal root carries sensory fibres into the spinal cord and contains a ganglion, known as the dorsal root ganglion.
Outline the ventral root
The ventral root carries motor fibres out of the spinal cord and does not have ganglion on it. Sympathetic fibres that leave the cord also leave via the ventral root.
Describe the arrangement of white and grey matter in the spinal cord
Within the spinal cord itself is the grey matter in the centre in an ‘H’ shape, and the white matter tracts around the outside. The grey matter forms two dorsal horns and two ventral horns.
Where do sensory neurones and motor neurones enter and move through the spinal cord?
Sensory neurones enter the cord via the dorsal root and pass through the dorsal horn. Motor neurones pass through the ventral horn and out via the ventral root.
What is the dorsal ramus?
Shortly after the spinal nerve is formed, it divides into two rami, a dorsal ramus that contains both sensory and motor fibres supplying dorsal structures (such as the skin over the back and paraspinal muscles), and a larger ventral ramus that carries sensory and motor fibres to ventral structures.
What are thoracic ventral rami renamed?
Intercostal nerves
What are spinal tracts and how are they named?
To carry information along a long distance, such as from the brain to the distal limb, or from the limb to the brain, the pathway may be split into several neurones. The first neurone in the pathway is called the first order neurone. The second neurone is called the second order neurone and so on.
Describe the make up of the ascending sensory pathways
In ascending sensory pathways, there are typically three neurones:
* First order neurone – from the receptor to the CNS (spinal cord or brainstem). The cell bodies of these neurones are in the dorsal root ganglion.
* Second order neurone – from the spinal cord or brainstem to the thalamus.
* Third order neurone – from the thalamus to the somatosensory cortex.
Describe the make up of the descending motor pathways
For descending motor pathways, there are typically two neurones:
* First order neurone (upper motor neurone) – from the motor cortex to the ventral horn of the spinal cord.
* Second order neurone (lower motor neurone) – from the spinal cord to the target muscle.
What is decussation?
At some point along their path, a neurone in most of the ascending or descending tracts will cross over to the contralateral side. This crossing is known as the decussation. Different tracts decussate at different points.
What are spinal tracts?
Within the spinal cord, bundles of these neurones (axons) are organised into vertical columns within the peripheral white matter of the cord. These are known as spinal tracts. The tracts carry impulses from the brain to the periphery or vice versa.
Where are the dorsal columns medial lemniscus located and what info do they carry?
These sensory tracts are located dorsally in the spinal cord and carry sensory information about fine touch, two-point discrimination, vibration and proprioception.
Where do the first order neurons enter the spinal cord in the DCML?
The first order neurones enter the spinal cord via the dorsal root and enter the ipsilateral dorsal columns.
What are the two pairs of tracts of the DCML?
The dorsal columns are divided into two distinct tracts on each side, the fasciculus gracilis (located medially) and the fasciculus cuneatus (located laterally). The fasciculus gracilis carries information from the lower limbs, whilst the fasciculus cuneatus carries sensory information from the upper limbs.
What happens when the first order neurons of the DCML reach the medulla?
Once the first order neurones reach the medulla, they synapse at their named nuclei: the gracile and cuneate nuclei.
What happens to the second order neurons after the synapse at the gracile and cuneate nuclei?
- After the synapse, the second order neurones decussate within the medulla, and the tract continues to the thalamus on the contralateral side. This part of the tract is called the medial lemniscus. Because of this, the whole tract is called the dorsal column medial lemniscus (DCML) pathway.
Describe the formation of the third order neurons in the DCML
There is another synapse in the thalamus, and the third order neurones continue via the internal capsule to the primary somatosensory cortex in the parietal lobe
Where are the spinothalamic tracts located and what info do they carry?
These sensory tracts are located antero-laterally in the spinal cord and carry sensory information about crude touch, pain and temperature.
Outline the first order neurones of the spinothalamic tracts
Once the first order neurones enter the spinal cord via the dorsal root, they synapse within the dorsal horn.
Outline the second order synapse of the spinothalamic tracts
After the synapse, the second order neurones decussate in the spinal cord, usually after travelling upwards one or two vertebral levels, and the tract continues to the thalamus on the contralateral side
Outline the third order neurones of the spinothalamic tracts
There is another synapse in the thalamus, and the third order neurones continue via the internal capsule to the primary somatosensory cortex in the parietal lobe.
Where are the lateral corticospinal tracts and what impulses do they carry?
These motor tracts are located laterally in the spinal cord and carry motor impulses.
Outline the first order neurones of the lateral corticospinal tracts
- The first order neurones (upper motor neurones) leave the motor cortex and pass through the internal capsule. They decussate within the medulla at the level of the medullary pyramids and continue contralaterally in the spinal cord.
- Once the first order neurones reach the desired spinal cord level, they synapse within the ventral horn.
Outline the second order motor neurones of the lateral corticospinal tract
After the synapse, the second order neurones (lower motor neurones) leave the cord via the ventral root towards the target muscle.
Where are the anterior and posterior spinocerebellar tracts and what do they carry?
These sensory tracts are located most laterally in the cord and carry unconscious proprioceptive information to the cerebellum.
Outline the anterior spinocerebellar tracts
The anterior, or ventral, spinocerebellar tract decussates twice, once at the level of entry into the cord, and again as soon as it enters the cerebellum through the superior peduncle. It therefore terminates ipsilaterally to side that it entered the cord.
Outline the posterior spinocerebellar tracts
The posterior, or dorsal, spinocerebellar tract does not decussate at all, so also reaches the cerebellum on the ipsilateral side.
What causes Brown-Sequard syndrome
This syndrome is caused by damage to one side of the cord only (hemisection of the cord). In clinical practice, it is quite a rare injury but causes characteristic findings on examination that explain the decussations of the tracts.
How does the presentation of Brown-Sequard syndrome let you find the place?
If a patient suffers damage to the left-hand side of their spinal cord, for example, then descending lateral corticospinal tract fibres are interrupted on the left side. Ascending dorsal column fibres on the left side are also interrupted. However, the ascending spinothalamic fibres that are interrupted on the left side had already decussated, therefore they were providing sensory information about the right side.
How would you test for Brown-Sequard syndrome?
In this example, clinical examination below the level of the lesion would reveal loss of motor control of muscles on the left, loss of two-point discriminative touch, vibration and proprioception sensation on the left, but loss of pain and temperature sensation on the right from one or two levels below the lesion.
What is contained in the rostral (upper) part of the basal ganglia?
-Striatum
-Putamen
-Caudate nucleus
-Globus pallidus
-Internal segment (Gpi)
-External segment (Gpe)
What is included in the caudal (lower) part of the basal ganglia?
-Subthalamic nucleus
-Substantia nigra
What are the two parts of the basal ganglia?
-Rostral (upper) part
-Caudal (lower) part
