Introduction to CNS anatomy Flashcards
What does the nervous system enable the body to react to? What are the two main divisions of the nervous system?
The nervous system enables to body to continously react to changes to both the internal and external environment. To main divisions are the central and peripheral NS.
What further divisions do the central and peripheral NS’s split into?
Central NS: Brain, spinal cord cranial nerve II (optic nerve) and the retina.
Peripheral NS: Spinal nerves and cranial nerves (except CN II) , autonomic NS (parasympathetic and sympathetic divisions) somatic motor and somatic sensory nerves (part of the spinal nerves).
How do spinal nerves leave the spinal cord?
Paired, via intervertebral foramen.
What are the two main cell types of the nervous system?
Neurons and neuroglia. Neurons work in harmony with neuroglial cells (also called glial cells).
What are the main characteristics of neurons?
Main characteristics:
- Structural and functional units of the NS
- Afferent (sensory) and efferent (motor)
- Interneurons (patellar reflex)
- Allow rapid communication via synapses and Neurotransmitters.
Describe general neuron structure.
Neurons have a general structure:
Dendrites: projections sensitive to NT’s at gap junctions
Cell soma/ body: metabolic centre of the neuron
Axon: Long projection from cell body to other neuron
Axon terminal: portion of the axon which communicates with other neurones/ body tissues via SYNAPSES.
What are the main characteristics of neuroglial cells?
- Non- neural/ non exictable
- Supporting cells, nourish and insulate neurons.
- x5 more abundant
What are the types of neuroglial cells in the Central NS?
4 types of neuroglial cells:
1) Oligodendrocytes- myelinate and provide structural framework
2) Astrocytes- Maintain BBB, recycle NT’s
3) Microglial cells- clear debris and pathogens via phagocytosis
4) Ependymal cells- Line ventricles of brain and central spinal canal, produce CSF.
What are the main types of neuroglial cells in the Peripheral NS?
1) Schwann cells - myelinate axons of peripheral nerves
2) Satellite cells- regulate nutrient and NS levels in the ganglia.
What are spinal nerves? What are the divisions of each (i.e what type of information is involved in each branch?)
They are mixed motor and sensory nerves. Sensory information can be: 1) visceral sensory (organs and vessels 2) somatic sensory (tissues) 3) special sensory (taste) Motor information can be: 1) somatic motor - skeletal muscle 2) Visceral/ autonomic motor 3) Branchiomotor- provide motor innervation to pharyngeal arches
Describe the formation of the neural tube:
Where does the nervous system develop from? what week does this happen?
What happens to form the neural tube?
What are the open ends of the neural tube called?
When do they close?
- The nervous system forms from the ectodermal plate at the beginning of week 3.
- The edge of the ectodermal plate thickens and becomes folds.
- These folds start to lift away from the rest of the ectodermal plate and fuse within the midline- forming the neural tube.
- The fusion first begins in cervical region and then continues towards the head and caudal regions.
- The open ends of the neural tube form the cranial and caudal neuropores.
- The cranial neuropore closes at day 25 and the caudal neuropore at day 27.
What can go wrong with neural tube folding?
What key prenatal supplement can prevent this?
- If the cranial neuropore does not close (day 25) it can result in anencephaly (absence of the brain) or mesoanencephaly ( herniation of brain tissue through partially formed cranium).
- If the caudal neuropore does not close (day 27) is results in spina bifida.
- Spina bifida ranges in severity - milder form = spina bifida occulta.
- Spina bifida occulta= failure to close neural arches of lumbar/ sacral vertebrae.
- Folic acid is a key prenatal supplement
Describe the development of the adult brain:
how many primary brain vesicles form and at what week?
what are they called?
How many secondary brain vesicles come from these?
what are they called?
What week does this occur?
What do the secondary brain vesicles go on to form?
They go on to form the adult brain, vesicles, brainstem and cerebellum.
- Telencephalon- cerebral hemispheres
- Diencephalon- thalamus and hypothalamus
- Mesencephalon- midbrain
- Metencephalon- cerebellum and pons
- Myelencephalon- medulla
What develops between the cerebral hemispheres and the thalamus/ brainstem?
If this didnt develop what could occur?
A flexure develops between the cerebral hemispheres and the thalamus/ brainstem.
This means the superior portion of the cerebral hemispheres can be described as dorsal.
The inferior portion of this flexure can be described as ventral.
If this flexure didnt develop our eyes would point upward.
What divides the two hemispheres of the brain?
What could a raised portion of the cerebral hemispheres be described as?
what could depressions/ folds in the cerebral hemispheres be described as?
What divides the temporal lobe from the rest of the brain?
The longitudinal fissure divides the L and R sides of the brain.
Raised portions described as a gyrus.
depressions = sulci.
The lateral / sylvian fissure divides the temporal lobe from the rest of the brain/
What is the name of a distinct white matter tract that connects the R/L hemispheres?
What forms the brainstem?
What structure sits below the corpus callosum and above the brainstem?
What structure comes of inferiorly to this?
What are these two structures collectively known as?
- The corpus callosum is a distinct white matter tract.
- Brainstem: Midbrain, pons. medulla.
- The thalamus sits below the corpus callosum and above the brainstem.
- The hypothalamus comes off inferiorly to the thalamus, ending in the pituitary gland inferiorly.
- Hypothalamus plus thalamus = Diencephalon
Label the image
What other structure does the corpus callosum intersect with?
What does this structure do?
- The corpus callosum (connecting R and L hemispheres) intersects with another white matter tract called the corona radiata.
- The corona radiata carries ascending and descending tracts between the cerebral cortex, thalamus and spinal cord.
What sulcus divides the frontal and parietal lobes?
What lies immediately anterior to this sulcus?
And posteriorly?
What sulcus divides frontal lobe from temporal?
How many gyri are there on the temporal lobe?
- The central sulcus divides the frontal and parietal lobes.
- Anteriorly to central sulcus is the precentral gyrus which is the primary motor cortex of the frontal lobe.
- Posteriorly is the post central gyrus which is the primary somatosensory cortex of the parietal lobe.
- Lateral sulcus/ sylvian fissure divides the frontal lobe from the temporal lobe.
- There are 3 gyri on the temporal lobe: 1) superior temporal gyrus 2) middle temporal gyrus 3) inferior temporal gyrus
what lobe is underneath the lateral sulcus/ sylvian fissure?
What are its functions?
- The insular lobe lies underneath the lateral sulcus.
- Involved with higher pain processing, emotion and language processing.
What divides the parietal lobe from the occipital lobe?
What sulcus is on the occipital lobe that has a key function?
- The parieto-occipital sulcus divides the parietal lobe from the occipital lobe.
- On medial aspect of the occipital lobe is the calcarine sulcus that forms the primary visual cortex.
What is the cingulate gyrus?
what system is it a part of?
where can it be found?
- The cingulate gyrus is an integral part of the limbic system
- It can be found superior to the corpus callosum on the medial aspect of the cerebrum.
- Has important functions in higher autonomic control such as HR, RR and pain processing.
What are key Brodman areas that relate to motor function?
- Brodmann areas 4 and 6
- Brodmann area 6 on precentral gyrus = primary motor cortex- controls contralateral motor body functions
- Brodmann area 4 just before area 6 is the permotor cortex- involved with retrieval of motor programs.
- Pre motor cortex involved in well known movements- eg tucking hair behind your ear.
What brodmann area is important for sensory information?
What other area may communicate with this area?
- Brodmann area 1 is the post central gyrus which is the primary somatosensory cortex which receives sensory input from the contralateral side of the body. (including taste).
- Brodmann area 17 is the primary visual cortex and receives contralateral information from the eyes. Communicates with the sensory cortex to process information.
What brodmann area is associate with hearing and where is it located?
- Brodmann area 41 is the primary auditory cortex and receives bilateral auditory sensory input
What is the general rule regarding the functionality of the L and R lobes?
- The L lobe looks after the R sided functions and vice versa.
- L lobe looks after R Motor, sensory, stereognosis (ability to perceive depth), body image, visual fields).
- R lobe looks after L Motor, sensory, stereognosis (ability to perceive depth), body image, visual fields).
What other functions does the L lobe control that is not specific to the right side of the body?
- Language
- Speech
- Writing
- Bilateral audio
What other functions does the R hemisphere look after that is not directly related to the left side of the body?
- Bilateral audio
- Spatial recognition
- Facial recognition
How are sensory and motor functions mapped onto the cortex?
Why does knowing about these regions help in clinical context?
What would help determine between the sensory/ motor map?
What does the size of the cerebral region tell you about function?
- Sensory and motor functions are mapped onto specific regions of the cerebral cortex.
- Knowledge of these regions is important when there is trauma to the cerebral cortex. May affect function focally or have more widespread effects.
- The sensory map includes the genitalia on the medial portion of the longitudinal fissure. From there generally follow up to feet, knees, hips, legs, trunk, neck, shoulders, arms, hands, face, mouth, pharynx.
- The greater the proportion of the cerebral cortex dedicated to a particular area, the more important its function. E.g. large proportion of motor cortex dedicated to hand movement due to many fine movements of the hands.
What is the brain covered in?
What lies deep to this?
What lies even deeper in subcortical areas?
What lies centrally in the brain around the thalamus that contains CSF?
- The brain is covered in dense grey matter = the cell bodies of neurones
- Lying deep to this is white matter tracts- the myelinated axons of the cell bodies that connect to other brain regions
- Deeper still are groups of cell bodies called nuclei.
- Nuclei= collections of cell bodies of neurones at a synaptic region with similar functions and projections.
- The ventricles of the brain sit centrally and produce CSF (ependymal cells) and circulate it.
Name these white matter tracts
what is each tract’s function?
- Corpus callosum- connects R and L cerebral hemispheres
- Corona radiata- white matter tracts of ascending/ descending tracts from cerebral cortex to thalamus and spinal cord
- Internal capsule- thin region of white matter tracts containing axons of neurones projecting to and from cerebral cortex to spinal cord. Becomes the corona radiata.
Define a nucleus
What are the nuceli of the basal ganglia?
How might they be paired and what do they form?
What is another structure that is a very large nucleus?
- A nucleus is a collection of neuronal cell bodies at a point of synapse with similar functions and projections.
- The basal ganglia is formed of three nuceli:
- Putamen
- Caudate
- Globus pallidus
- Sometimes these nuclei are paired, always the putamen with:
- Putamen and globus pallidus = lentiform nucleus
- Putamen and caudate = striatum
- The thalamus is a large collection of nuclei with multiple functions.
What does the brainstem contain? (not referring to midbrain/ pons/ medulla)
Brainstem contains multiple important nuclei for the cranial nerves and the cerebellum.
What do primary cortical regions allow?
What do secondary and association areas allow?
- Primary cortical regions allow the original perception of vision, sensation, sound
- Secondary and association areas allow us to interpret this information by relating it with information from other regions, allowing us to associate it with texture, smell, emotion and previous experiences.
- Secondary/ association areas allow us to put this information into memory
Name condition for inability to describe faces
- Prosopagnosia
What three types of fibres enable the connection of the cerebral cortex to subcortical and other cortical areas/ spinal cord?
- Association fibres connect regions within a hemisphere
- Commisural fibres connect cerebral hemispheres (e.g corpus callosum)
- Projection fibres connect cerebral cortex to brainstem/ spinal cord (internal capsule).
What do complex functions require?
What is a fasciculus?
Describe the process for seeing a book cover, understanding the text and speaking about it.
What happens if one of these key areas is affected?
- Complex functions require multiple connections between different brain regions.
- Fasciculus= bundles of fibres sharing similar function and route of travel
- Upon seeing book cover this information would be sent to the primary visual cortex (area 17)
- Information then sent to another area of the cortex for understanding letters/ writing
- This information is sent to wernicke’s area which allows us to understand and interpret written and spoken word
- This is then sent to Broca’s area by the arcuate fasciculus.
- Broca’s area allows us to speak as it is involved in the motor planning of speech.
- Aphasia can occur if there is damage to either brocas or wernickes area.
List the cranial nerves
Describe where the cranial nerves arise from in the brain?
- Cranial nerves I and II arise directly off the forebrain
- Cranial nerve IV (trochlear) is the only CN to arise off the dorsal aspect of the brainstem- all others are ventrally.
- Cranial nerves III- X and XII arise of nuceli within the brainstem
- Cranial nerve XI - accessory nerve - arises of the medulla and spinal cord (c1-c5).
Describe the structure of the three regions of the brainstem in anterior view
- Three regions are the midbrain, pons and medulla
- On the midbrain can see there are cerebral peduncles forming passageways that carry multiple different tracts
- Inbetween the cerebral peduncles is the interpeduncular fossa with cranial nerves iii coming off this region and mamillary bodies above.
- On the pons can see large CN V (trigeminal) coming off either side
- Cerebellar peduncles connect the pons to the cerebellum
- At the ponto-medullary junction have CN 7/8/9 coming off
- Inferior to this are the olives
- Then the pyramidal tracts which carry descending corticospinal tracts
- Pyramidal decussation- the point at which the pyramidal tracts cross over.
Describe the posterior view of the brainstem and particular structures:
- Superiorly you can see the two thalamic lobes, with the 3rd ventricle inbetween
- Inferior to the thalamus see the superior and inferior colliculi
- Superior colliculus- relay nucleus for visual reflexes
- Inferior colliculus- relay nucleus for auditory reflexes
- Inferior to this is the Trochlear nerve (CN IV) the only nerve to arise off the dorsal aspect of the brainstem.
- Then the superior, middle and inferior cerebellar peduncles whcih connects the cerebellum to the midbrain, pons and medulla respectively.
- On the floor of the pons is the floor of 4th ventricle which lies between upper medulla, pons and cerebellum.
- On the medulla are the dorsal column nuclei and dorsal columns associated with ascending sensory tracts from the dorsal column-medial lemniscal pathway.
Describe the structure of the cerebellum
What is its main function?
- Cerebellum has a large surface area with many folds called folia.
- Has multiple inputs and outputs
- Large surface area essential for its function
- Primary function = coordination and planning of movement
- Formed of two main lobes connected by a vermis
What are the three main lobes of the cerebellum?
What would damage to one side of the cerebellum cause?
- Three main lobes of the cerebellum are the anterior, posterior and flocculonodular lobe.
- Cerebellar damage would cause damage on the ipsilateral (same) side as each cerebellar lobe looks after its own side (L w/ L and R w/ R).
Describe the blood supply to the brain
- Via the circle of willis which is supplied by 2x vertebral arteries and 2x internal cartoid arteries.
- Internal carotid arteries give off the middle cerebral artery and anterior communicating artery
- From anterior communicating artery have the anterior cerebral artery
- Off the middle have the posterior communicating artery which connects to the posterior cerebral artery
- These are joined to a large singular artery overlying the pons called the Basilar artery
- Basilar artery gives off anterior superior and anterior inferior cerebellar arteries
- The basilar artery is formed by the union of the two vertebral arteries
- Off the two vertebral arteries come the posterior inferior cerebellar arteries.
Describe the meningeal layers of the brain and spinal cord:
What are the dural venous sinuses formed by?
- Dura mater- formed of two layers 1) outer, fibrous, leathery periosteal layer 2) inner meningeal layer
- Arachnoid mater with its CSF filled subarachnoid space, in which the cerebral veins run
- Pia mater which lies directly over the cerebrum, joins with ependyma which secrete CSF.
- Normally the two dural layers (periosteal and meningeal) lie very close to each other. Separation of the inner meningeal layer from the dural layer forms the dural venous sinuses which become filled with venous drainage from the cerebral hemispheres.
- Valveless and endothelial lined.
- This meningeal layer also dives into the cerebrum at certain regions to support it - forming folds
Name each of the venous sinuses shown
What coud blockage of any of the dural venous sinuses lead to?
Where do all the venous sinuses drain into?
- Venous sinuses drain into the internal jugular veins
What are dural reflections?
What key structures are shown and what is their function?
- Dural reflections are reflections of the meningeal layer of the dura mater into the cerebrum. Acts to support and stabilise the structure of the cerebrum.
- Superior- falx cerebri separates the R and L hemispheres, prevents movement of hemispheres during axial rotation
- Falx cerebelli- similar to above, prevents excessive movement of R and L cerebellar lobes during axial head rotation
- Tentorium cerebelli- separates occipital lobe from cerebellum, prevents occipital compression of cerebellum during neck flexion and extension.
- Diaphragm sellae - protective pocket for pituitary
Describe the structure of the brain ventricles
What could happen if there was blockage of the CSF flow?
what is the function of CSF?
- Have two paired lateral ventricles that connect to the 3rd ventricle via the interventricular foramen.
- The 3rd ventricle sits inbetween the two thalamic lobes
- 3rd ventricle becomes the 4th ventricle via the aqeduct.
- Hydrocephalus could occur if there was blockage to CSF flow
- CSF bathes the brain, giving it buoyancy, and nourishes and protects it.
