Nervous System Topography Flashcards
Describe Grey Matter
- Composed of cell bodies and dendrites primarily
- Highly vascular
- Most computation occurs here
- Contains some axons, in order to communicate with white matter
Describe White Matter
- Composed of axons
- White due to presence of fatty Myelin
What are the PNS equivalents of Grey and White matter?
Grey- Ganglia (Not basal ganglia, these are part of CNS)
White- Peripheral nerves
What is a Nucleus?
What is a Cortex?
Nucleus: A collection of functionally related cell bodies
Cortex: A folded sheet of cell bodies found on the surface of a brain structure
What is a fibre?
What are the 3 types of fibre?
An axon in association with its supporting cells
- Association fibres
- Commissural fibres
- Projection fibres
What do Association fibres connect?
Connect cortical region within a single hemisphere
E.g Parietal and temporal lobes of same hemisphere
What do Commissural fibres connect?
Connect the Left and Right hemispheres
E.g Corpus Callosum
What do Projection fibres connect?
Connect the cerebral hemispheres with the cord/brainstem and vice versa
(E.g Corticospinal fibres or Spinothalamic fibres)
Describe the spinal cord
- 31 segments
- Central grey matter core, outer white matter shell
- Each segment connects with a Spinal (mixed) nerve via Ventral (motor) and Dorsal (sensory) nerve roots
(Roots are actually formed from convergence of multiple rootlets)
What is a Funiculus?
A segment of white matter containing multiple distinct pathways which both ascend (sensory) and descend (motor)
What is a Tract?
These are found in Funiculi
A white matter pathway connecting 2 regions of grey matter, in which impulses travel in a single direction only
E.g;
- Dorsal funiculus contains dorsal column tract (ascends)
- Lateral funiculus contains lateral corticospinal tract (descends) and spinothalamic tract (ascends)
- Ventral funiculus contains ventral corticospinal tract (descends)
What is a Fasciculus?
(Found in Tracts)
Compare the 2 Fasciculi of the Dorsal Column Tract which is prt of the Dorsal Funiculus
A subdivision of a tract that supplies a distinct body region
- Fasciculus gracilis/ Gracile Fasciculus supplies lower body half
- Fasciculus cuneatus/ Cuneate Fasciculus supplies upper body half
Describe the organisation of the grey matter of the spinal cord
- Cell bodies are organised into cell columns
- These columns are organised into Laminae
List the Key function of the parts of the Brainstem
Midbrain;
- Eye movement
- Reflex responses to sound and vision
Pons;
- Feeding
- Sleep
Medulla;
- Cardiovascular and respiratory homeostasis
- Contains a major motor pathway (medullary pyramids)
What are the Cerebral peduncles of the Midbrain?
Areas of white matter that contain descending corticospinal fibres from the Ipsilateral hemisphere
What is the Substantia Nigra of the midbrain?
Area of grey matter containing dopaminergic neurons that project to the Striatum (Nigrostriatal fibres)
What is the Red Nucleus of the midbrain?
An area of grey matter that gives rise to axons that travel to the spinal cord in the Vestigial Rubrospinal tract
(Has some motor functions)
What is the Oculomotor nucleus of the midbrain?
- An area of grey matter containing
- lower motor neurone cell bodies that
- project though the oculomotor nerve
- to all except 2 of the extra ocular muscles
What is Periaqueductal grey matter of the midbrain?
An area surrounding the cerebral aqueduct that has roles in;
- Pain transmission
- Micturition
What 2 ventricles are connected by the Cerebral Aqueduct?
3rd ventricle and 4th ventricle
List 2 structures that pass through the midbrain to get to the thalamus
- Medial lemniscus (Connects Gracile/ Cuneate nuclei to thalamus)
- Spinothalamic tract (Connects spinal dorsal horn to thalamus)
What do the Superior and Inferior Colliculi of the midbrain do?
These are regions of grey matter
Superior: Regulates reflex responses to visual stimuli
Inferior: Regulates reflex responses to auditory stimuli
List 4 key features of the midbrain
- CN V exits from lateral aspect
- Corticospinal fibres travel ventral
- Beneath 4th ventricle so can get compressed if this expands
- Contains reticular formation regions important for sleep
Describe the Medullary Pyramids (white matter)
Ventral swellings containing corticospinal fibres from the Ipsilateral hemisphere.
(These fibres decussate in the caudal medulla at the decussation of the pyramids)
A Gyrus is a raised fold of cerebral cortex.
What sits anterior and posterior to the central gyrus?
Anterior: Precentral gyrus (Contains primary motor cortex)
Posterior: Postcentral gyrus (Contains primary sensory cortex)
Which lobes are separated by the Sylvian/ Lateral fissure?
Temporal lobe separated from frontal and parietal lobes
Is the Parieto-Occipital sulcus visible on a Superfical view?
No
The Primary Visual Cortex surrounds the Calcarine Sulcus of the Occipital lobe.
Compare the functions of the visual cortex above and below the Calcarine Sulcus
Above: Supplies the contralateral inferior visual field
Below: Supplies the contralateral superior visual field
Describe the Uncus
- Most medial part of temporal lobe
- Contains the olfactory cortex
- Can herniate below Tentorium Cerebelli
What is the Parahippocampal Gyrus?
Part of the medial temporal lobe that provides input to the underlying hippocampus
(Key region for memory encoding)
Describe the Thalamus
- Important for conscious sensation
- Acts as a sensory relay station projecting to the Primary sensory cortex
Describe the role of the Cingulate Gyrus
- Important role in emotion and memory
- Participates in the Papez Circuit
Describe the Fornix
- A major output pathway from the Hippocampus
- Part of the Papez Ciruit
Describe the Tectum
- Posterior part of midbrain
- Contains the Superior and Inferior Coliculi (so involved in regulation of the reflex responses to auditory and visual stimuli)
Describe the Cerebeller Tonsils
Part of the cerebellum that can herniate through the Foramen Magnum and compress medulla
(Therefore raised ICP can lead to death through cardiorespiratory compromise)
Brain ventricles are hollow cavities containing CSF
What do each of them contain?
Choroid plexus, which is highly vascular and makes 600-700ml of CSF a day
What are 2 functions of CSF?
Mechanical: Shock absorbs the brain and renders it weightless
Metabolic: Contains glucose and maybe hormones
Describe briefly the circulation of CSF
- Circulates through ventricular system and subarachnoid space
- Reabsorbed at Arachnoid granulations (Cauliflower-resembling projections into Superior Sagittal sinus) by entering Venous Blood
Which ventricles are the largest and make the most CSF?
What are the 3 parts of these ventricles
Lateral ventricles (Large C shapes)
- Frontal horn (in frontal lobe)
- Temporal horn (in temporal lobe)
- Occipital horn (in occipital lobe)
Which brain ventricle sits below the Cerebellum
The 4th Ventricle
Describe the flow of CSF from the Lateral ventricles
Flows through Interventricular foramen into the 3rd Ventricle
(3rd ventricle is flattened in midline by the thalami on each side)
Describe the flow of CSF from the 3rd ventricle
Drains from 3rd to 4th Ventricle by the Cerebral Aqueduct of the Midbrain
Describe CSF flow once it enters the subarachnoid space
Bathes the superficial surfaces of the brain and spinal cord, before being reabsorbed in the arachnoid granulations
(Goes to RA then kidney to be excreted)
How would the Lateral, 3rd and 4th ventricles be affected in blockage of the cerebral aqueduct
Lateral- Dilated
3rd- Dilated
4th- Normal
Describe CSF flow as it exits the 4th Ventricle
Drains into Subarachnoid space via 2 Lateral and 1 Median Apertures
Negligible drainage via central canal of the spinal cord
(Lateral- Foramen of Luschka, Median- Foramen of Magendie)
