1.1 intro and basic topography Flashcards
What are the basic components of the cns?
Cerebral hemispheres
Brainstem and cerebellum
Spinal cord
What are the basic components of the pns?
Dorsal and ventral roots
Spinal nerves
Peripheral nerves
True or false: because the Cauda equina lies in the cranial cavity, it is in the central nervous system.
False
Cranial cavity doesn’t automatically mean its in the cns
What is grey matter composed of?
Cell bodies and dendrites, its highly vascular
In the central nervous system
( has some axons to communicate with white matter)
In PNS = grey matter = ganglion = collection of cell bodies
What is white matter composed of and why is it white?
It’s composed of axons
(Myelinated and unmylinated) It’s white because of the presence of fatty myelin
In the PNS is termed a nerve or root.
What is the pns equivalent of grey and white matter?
Grey after = ganglion (connecting cell bodies) was
Whit matter = peripheral nerve
What is the basic structure of a spinal cord segment?
- 31 segments each supplying a dermatome and myotonic on each side
- central grey matter and outer white matter
- connects with a spinal nerve through dorsal sensory and ventral motor roots
- if you know the dermatome/myotome, you can localise the lesions to a given cord segment
What type of matter makes up the cerebral cortex?
Grey matter
What is a funiculius?
A segment of white matter containing multiple distinct tracts. Impulses travel in multiple directions
What is a tract of white matter?
An anatomically and functionally defined white matter pathway connecting two distinct regions of grey matter. Impulses travel in one direction (either ascending or descending)
This is how white matter is arranged
What is a fasciculus of white matter?
A subdivision of a tract supplying a distinct region of the body.
How is grey matter arranged?
Into cell columns
What is a nucleus of grey matter?
A collection of functionally related cell bodies
What is a cortex of grey matter?
A folded sheet of cells bodies found on the surface of a brain structure.
What is a fibre of white matter?
A term relating to an axon in association with its supporting cells. Used synonymously with axon.
- association fibres connect cortical regions with the same hemisphere e.g U fibres
- commissary fibres connect left and right hemispheres, or cord halves e.g the corpus callosum
- projection fibres connect the cerebral hemispheres with the cord/brainstem and vice versa
What is the function of the midbrain?
Eye movements and reflex responses to sound and vision
What is the function of the pons?
Feeding and sleeping
What is the function of the medulla?
Cardiovascular and respiratory pathway and medullary pyramids
Where is CSF made?
The choroid plexus
In every brain ventricle, the most being made in large lateral ventricles (sit deep in the hemispheres)
Highly vascular choroid plexus and makes 600-700ml of CSF a day.
Why is the brain hollow?
It’s developed from a hollow tube, so has hollow cavities called brain ventricles. These ventricles each contain choroid plexus which makes csf.
Where is CSF reabsorbed?
At arachnoid granulation mainly
(Resemble little cauliflowers, projecting into the superior Sagittal sinus. Here CSF crosses the wall of the granulation and enters venous blood)
What are the three primary brain regions for the
- forebrain
- midbrain
- hindbrain
Forebrain = prosencephalon
Midbrain = mesencephalon
Hindbrain = rhombencephalon
After neural tube closure in 4th week these dilations at the cranial end become the three primary brain vesicles
What are flexures in the CNS?
Growth and development at cranial neural tube exceeds availability of space linearly so it must fold up.
Cervical floured is at the spinal cord - hindbrain junction
Cephalon flexure at the midbrain region as well.
Thus the neuraxis doesnt remain straight.
How does a ventricular system develop in the cns?
Tubular structures of the developing CNS persists as development proceeds
In the adult, comprised of interconnected reservoirs filled by csf produced by cells of ventricular lining
Role: to cushion brain and spinal cord within their bony cases
What abnormalities can occur in the ventricular system?
Hydrocephalus
Most common in newborns suffering from spina bifida (readily treatable by use of shunt)
Can occur where there is any blockage of the ventricular system e.g tumour or infection
What are the layers of the neural tube from inside out?
- neural epithelial layer
- intermediate mantle layer with neuroblasts
- marginal layer with processes
Roof and flow plates regulate dorsal and ventral patterning
Alar plate = sensory
Basal plate = motor
How do you get a neural crest in cns formation?
Cells of the lateral border of the neuralectoderm tube
They become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition
Where do functions e.g eye movement, swallowing and cardiorespiratory homeostasis take place?
In the brainstem and cerebellum
What are the ascending and descending pathways in the spinal cord?
Ascending = sensory Descending = motor
How does CSF flow?
In every brain ventricle, the most being made in large lateral ventricles (sit deep in the hemispheres) and circulates to interventricular foramen into the third ventricle (squashed flat in the mid line by the thalamus on each side).
Drains from third ventricle to the fourth via the cerebral aqueduct (in the midbrain)
Fourth ventricle sirs beneath the cerebellum and CSF can drain from it via the lateral (of Luschka) and median (of magendie) apertures. (Holes in the beak for CSF to drain from ventricular system into subarachnoid space)
Once in subarachnoid space CSF percolates around the superficial surface of the brain and spinal cord before being ewabsodbed in franhlations
What effect can blockage of the ventricular system have?
Blockage of a part of the ventricular system will lead to upstream dilatation and potential
damage to structures surrounding the dilated ventricles
The cerebral aqueduct is a common site for such occlusions, maybe due to congenital stenosis or tumour
Blockage of the aqueduct would cause dilatation of the lateral and third ventricles but with a normal fourth ventricle (downstream)
