Brain topography and CSF circulation Flashcards
What are the basic components of the PNS?
- Dorsal and ventral roots
- Spinal nerves
- Peripheral nerves
What are the basic components of the CNS?
- Cerebral hemispheres
- Brainstem and cerebellum
- Spinal cord
From where do the CNS and PNS derive?
- CNS derives from neural tube
- PNS derives from neural crest cells
Outline the function of the cerebral hemispheres?
- Higher functions
- Motor and sensory (conscious)
- Emotion
- Memory
Outline the function of the brainstem and cerebellum
- Communication via cranial nerves
- Includes functions such as eye movement, swallowing, and cardiorespiratory homeostasis
- Cerebellum involved with motor sequencing and coordination
Outline the functions of the spinal cord
- Ascending (sensory) and descending (motor) pathways
- Spinal reflex arcs
- Control of upper and lower limbs at level of cervical and lumbosacral enlargements
What is grey matter formed from?
- Composed of cell bodies and dendrites
- Rich blood supply
- Reflects computational role of grey matter
- Some axons but not as many as in white matter
What is grey matter called in the PNS?
- Ganglion (collection of cell bodies)
What is white matter formed from?
- Myelinated and non-myelinated axons with no cell bodies
- Myelin is white
- White matter pathways connect areas of grey matter
- Passively conducts impulses
What is the PNS equivalent of white matter?
- Peripheral nerve or root
What is a nucleus?
- A collection of functionally related cell bodies
What is the cortex?
- Grey matter
- A folded sheet of cell bodies found on surface of a brain structure (cerebrum or cerebellum)
- Typically 1-5 mm thick
What is a fibre?
- Term relating to an axon in association with its supporting cells (e.g. oligodendrocytes)
- Synonymous with axon
What do association fibres do?
- Connect cortical regions within same hemisphere
What do commissural fibres do?
- Connect left and right hemispheres or spinal cord halves
- E.g. corpus callosum is biggest commissural fibre
What do projection fibres do?
- Connect cerebral hemispheres with cord/brainstem and vice versa
Outline the organisation of the spine
- 31 segments
- Each supplies a given dermatome and myotome on each side
- Each segment connects with a spinal (mixed) nerve through dorsal (sensory) and ventral (motor) roots
- Knowledge of dermatomal and myotomal supply allows location of lesions to a given cord segment
What is the structure of the spinal cord like?
- Cord has a central core of grey matter and an outer shell of white matter
Why is the spinal cord shorter than the vertebral column?
- Bones of vertebral column grow faster than spinal cord itself
- Leads to formation of cauda equina
What forms spinal nerve roots?
- Convergence of multiple rootlets, which plug directly into the cord
What does a sensory deficit in a dermatomal pattern suggest?
- Lesion is at level of dorsal roots or spinal nerves
What does a sensory deficit across multiple segments suggest?
- Cord lesion
What does a sensory deficit in a homuncular pattern suggest?
- Lesion above thalamus
Define funiculus
- Segment of white matter containing multiple distinct tracts
- Impulses travel in multiple directions
Define what a tract is
- An anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter
- Impulses travel in one direction
Define what a fasciculus is
- A subdivision of a tract supplying a distinct region of the body
How is the grey matter of the spinal cord organised?
- Cell bodies of grey matter are organised into cell columns
- Motor neurones supplying a given muscle arise from multiple segments and form a distinct population of neurones in the CNS - a nucleus
- Each nucleus controls a particular muscle
What does the midbrain (mesencephalon) control?
- Eye movements and reflex responses to sound and vision
What does the pons control?
- Feeding
- Sleep
What does the medulla control?
- Cardiovascular and respiratory centres
- Contains a major motor pathway (medullary pyramids)
- Medullary pyramids are formed of white matter
What does the central sulcus do?
- Sits in coronal plane
- Separates frontal and parietal lobes
What does the precentral gyrus do?
- Contains primary motor cortex
- Motor structures tend to sit anteriorly in CNS
What does the post central gyrus do?
- Contains primary sensory cortex
- Sensory structures tend to sit posteriorly in CNS
What does the lateral/Sylvian fissure do?
- Separates temporal lobe from frontal/parietal lobes
What does the parieto-occipital sulcus do?
- Separates parietal lobe from occipital lobe
- Only visible on medial aspect of cerebrum
What is the optic chiasm?
- Site where fibres in visual system cross over
What is an uncus?
- Sits close to midbrain and CN III
- Part of temporal lobe
- Can herniate and compress midbrain
- Olfactory cortex resides in uncus
What are the medullary pyramids?
- White matter
- Location of descending motor fibres
- All voluntary movement is carried down pyramids
What is the parahippocampal gyrus?
- Key cortical region for memory encoding
- Sits deep in temporal lobe
What is the calcarine sulcus?
- Key landmark in visual system
- Visual cortex above calcarine sulcus supplies inferior visual field
- Visual cortex below calcarine sulcus supplies superior visual field
What is the corpus callosum?
- Fibres connecting the cerebral hemispheres
- White matter
What is the thalamus?
- Sensory relay station projecting to sensory cortex
- Acts as final point before sensory information reaches cortex
- Contains cell bodies of third order neurones and projects to primary sensory cortex in a homuncular pattern
What is the cingulate gyrus?
- Cortical area important for emotion and memory consolidation
What is the hypothalamus?
- Found in walls of third ventricle
- Has important neuroendocrine and homeostatic roles
What is the fornix?
- Key output pathway of hippocampus
What is the tectum?
- Posterior part of midbrain
- Involved in involuntary responses to auditory and visual stimuli
What are the cerebral tonsils?
- Found on inferior aspect of cerebellum
- Can herniate through foramen magnum in cases of raised intercranial pressure
- Often lead to death due to cardiorespiratory compromise through compression of medulla
What are brain ventricles?
- Brain develops from a hollow tube
- Brain itself is hollow and contains cavity filled with CSF
- These cavities are brain ventricles
Which structure is found in the ventricles?
- Choroid plexus
- Highly vascular
- Makes a total of 600-700 ml CSF each day
What are the functions of CSF?
- Metabolic and mechanical functions
- Contains glucose and maybe hormones
- Cushions brain
- Buoyancy of brain
What are the arachnoid granulations?
- Reabsorb CSF
- Resemble little cauliflowers
- Project into superior sagittal sinus
- CSF then enters venous blood
Outline how CSF circulates through the ventricular system
- Most CSF is made in lateral ventricles
- CSF then circulates through interventricular foramen into third ventricle
- CSF drains from third ventricle to fourth ventricle via cerebral aqueduct
- CSF drains from fourth ventricle via lateral and median apertures
- CSF enters subarachnoid space
What happens to CSF after it has entered the subarachnoid space?
- CSF percolates around superficial surfaces of brain and spinal cord
- Is then reabsorbed by arachnoid granulations
What happens when there is a blockage in the ventricular system?
- Leads to upstream dilation and potential damage to structures surrounding dilated ventricles
- Cerebral aqueduct is common site for occlusions
- Would cause dilation of lateral and third ventricles but fourth ventricle is normal
