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.
