S1) Topography of the Nervous System Flashcards
What are the four basic components of the central nervous system?
- Cerebral hemispheres
- Brainstem
- Cerebellum
- Spinal cord
What are the four basic components of the peripheral nervous system?
- Dorsal and ventral roots
- Spinal nerves
- Peripheral nerves
- Ganglia
Distinguish between the composition of grey matter and white matter
- Grey matter is composed of cell bodies and dendrites (highly vascular)
- White matter is composed of axons with no cell bodies(+ supporting cells) connects ares of grey matter
Why does grey matter contain axon terminals?
Grey matter contains axons to allow communication with white matter
Why is white matter white?
White matter is white due to the presence of fatty myelin
In the peripheral nervous system, identify the equivalent structures of the following:
- Grey matter
- White matter
- The PNS equivalent of grey matter is a ganglion
- The PNS equivalent of white matter is a peripheral nerve
How many segments does the spinal cord consist of?
The spinal cord is composed of 31 segments
Describe the structure of a spinal cord segment
- Central core of grey matter
- Outer shell of white matter
Each segment connects with a mixed spinal nerve through dorsal sensory roots and ventral motor roots
Identify three components of white matter
- Funiculus
- Tract
- Fasciculus
What is a funiculus?
- A funiculus is a segment of white matter containing multiple distinct tracts
- Impulses travel in multiple directions, up and down
- dorsal funiciulus contains dorsal column tract (ascending)
- lateral funiciulus contains contains lateral corticospinal trac t (descending)
- spinothalamic tract (ascending)
- ventral funiculus contains ventral corticospinal tract (descending)
What is a tract?
- found within each funiculus
- A tract is an anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter
- Impulses travel in one direction, either up or down (sensory or motor)
- eg spinothalamic tract (connects spinal cord dorsal horn to thalamus)
What is a fasciculus?
A fasciculus is a subdivision of a tract supplying a distinct region of the body
- eg gracile fasciculus supplying lower half of body, cuneate fasciculus supplying upper half
Identify the three different regions of grey matter
What is a nucleus?
A nucleus is a collection of functionally related cell bodies (grey matter)
eg thalamus
What is a cortex?
A cortex is a folded sheet of cell bodies found on the surface of a brain structure (grey matter)
outer shell of grey mater found on cerebral hemispheres and the cerebellum
What is a fibre?
A fibre is an axon in association with its supporting cells e.g. oligodendrocytes (synonymous with axon)
What are the three types of fibres found in the nervous system?
- Association fibres
- Commissural fibres
- Projection fibres
What do association fibres do?
Association fibres connect cortical regions within the same hemisphere
What do commisural fibres do?
Commissural fibres connect left and right hemispheres or cord halves
What do projection fibres do?
Projection fibres connect the cerebral hemispheres with the cord/brainstem and vice versa
What are the three components of the brainstem?
What is the function of the midbrain (mesencephalon)?
The midbrain regulates eye movements and reflex responses to sound and vision
Which processes are regulated by the pons?
- Feeding
- Sleep
Which key centres are found in the medulla?
- Cardiovascular and respiratory centres
- Major motor pathway (medullary pyramids)
Where is the central sulcus found?
Central sulcus is a key landmark separating the frontal and parietal lobes (coronal plane)
Which cortices are found in the following locations:
- Precentral gyrus
- Postcentral gyrus
- Precentral gyrus: contains primary motor cortex
- Postcentral gyrus: contains primary sensory cortex
Where is the lateral fissure found?
The lateral fissure is a key landmark separating the temporal lobe from the frontal/parietal lobes
Where is the parieto-occipital sulcus found?
Parieto-occipital sulcus is a key landmark separating the parietal lobe from the occipital lobe
can only see this in the middle of the brain
Where is the calcarine sulcus found?
The calcarine sulcus is a key landmark surrounded by the primary visual cortex
What is the optic chiasm?
The optic chiasm is a site where fibres in the visual system cross over
What is the uncus?
- The uncus is a part of the temporal lobe that can herniate, compressing the midbrain
- It has an important olfactory role (smell)
part of hippocampus, emotions
What are the medullary pyramids?
The medullary pyramids are a location of descending motor fibres
this is a major pathway
What is the parahippocampal gyrus?
The parahippocampal gyrus is a key cortical region for memory encoding
What is the corpus callosum?
The corpus callosum consists of fibres connecting the two cerebral hemispheres otherwise left and right are not in coordinaton
What is the thalamus?
The thalamus is a sensory relay station projecting to the sensory cortex
the final point that sensory information has to pass to reach the thalamus
What is the cingulate gyrus?
The cingulate gyrus is a cortical area important for emotion and memory, grey matter
What is the hypothalamus?
The hypothalamus is an essential centre for homeostasis
What is the fornix?
The fornix is a major output pathway from the hippocampus
What is the tectum?
The tectum is the dorsal part of the midbrain involved in involuntary reflex responses to auditory and visual stimuli
What is the cerebellar tonsil?
The cerebellar tonsil is a part of the cerebellum that can herniate and compress the medulla
if there is an increase in intracranial pressure then this will force this area down and crush the medulla
Having developed from a hollow tube, the brain is itself hollow.
What are the cavities in the brain called?
The cavities in the brain are called ventricles
Describe the layout of the ventricular system
What is found inside the brain ventricles?
The ventricles each contain choroid plexus (highly vascular0 , which makes a total of 600-700ml of cerebrospinal fluid per day
What types of functions does CSF have?
CSF has both metabolic and mechanical functions
- it is important in supporting the brain and making it weightless
- contains glucose and good for immunity
Describe the circulation of cerebrospinal fluid
CSF circulates through the ventricular system and subarachnoid space before being reabsorbed at the arachnoid granulations in the superior sagittal sinus (and some other sites) and then gets reabsorbed into the venous system
what is a gyrus and a sulcus
- gyrus → raised fold of cerebral cortex
- sulcus → valley between adjacent gyri
what is a fissure?
- large groove in between adjured hemispheres (lobes)
pathway of the CSF through the brain ventricles
- choroid plexus makes CSF
- most CSF made in the lateral ventricles
- CSF then circulates through intraventricular foramen → third ventricle
- then drained to the fourth ventricle via the cerebral aqueduct
- CSF drains through 2 lateral apertures and median aperture in the 4th ventricle
blockage of the ventricular system
- blockage of a part of the system → upstream dilation and damage to surrounding structures
- cerebral aqueduct is a common sight due to stenosis or a tumour
- blockage of the cerebral aqueduct = dilation of 3rd and 2nd ventricles but normal 4th ventricle
what are cerebral peduncles (white matter) in the midbrain
- contain descending corticospinal fibres from ipsilateral hemispheres
what is substantia Nigra (grey matter) in the midbrain
- contains dopaminergic neurones that project to striatum
what is the red nucleus (grey matter) in the midbrain
- well distinct and gives rise to axons that travel to the cord in vestigial rubrospinal tract (controlling muscle tones and flexion)
what is the oculomotor nucleus (grey matter) in the midbrain
- contains lower motor neurone cell bodies projecting through oculomotor nerve to all bar two of extra ocular muscles
what is Edinger-Westphal nucleus (grey matter) in midbrain
contains parasympathetic preganglionic neurones that project to the ciliary ganglion in the orbit to cause pupillary constriction
what is Periaqueductal grey matter in the midbrain
Periaqueductal grey matter is an area surrounding the cerebral aqueduct that has roles in pain transmission and micturition
what are medial lemniscus and spinothalamic tract
medial lemniscus (connecting gracile/cuneate nucleus to thalamus) and spinothalamic tract (connecting spinal dorsal horn to thalamus) path through the midbrain (they have to get to the thalamus!
what is Superior/inferior colliculus (grey matter)
Superior/inferior colliculus (grey matter) regulate reflex responses to visual and auditory stimuli respectively
how are cell bodies in the grey matter cord organised
in columns
organised into laminae
which space do bridging veins traverse
subdural
what is another term for crus cerebri
cerebella peduncles that connect the cerebral hemispheres to the brainstem
what layer is the falx cerebri covered in
meningeal dura
what dura covers brain and the spinal cord
- occipital - cervical junction where the periosteal layer covering the brain turns into meningeal dura
