Cells & Tissues of The Nervous System Flashcards
What are the 2 different cell types that make up the nervous system?
Neurones and glial cells
What is a neurone?
Structural and functional unit, excitable cells and impulses carries as action potentials - typical neurone has multiple dendrites, a cell body, an axon which ends in synaptic terminals - high metabolic rate - long living and amitotic (lives entire life without being replaced so if lost is lost forever)
What are glial cells?
Non-excitable supporting cells and are much smaller than neurones
What are the different types of neurone?
Multipolar, pseudounipolar and bipolar
Describe a multipolar neurone.
Typical neurones seen in diagrams- all motor neurones carrying impulses from the CNS to periphery and interneurones =multipolar - their cell bodies are situated within the CNS
Describe a pseudounipolar neurone.
The action potential can go straight through bypassing the cell body so from dendrite to axon - these are sensory neurones and their cell bodies form ganglia of spinal and cranial nerves
Describe a bipolar neurone.
Found in cranial nerve 1 (olfactory) and 2 (optic)= 1 dendrite, 1 cell body and 1 axon
What is the myelin sheath?
Speeds up conduction in axons called ‘saltatory conduction’ by action potentials jumping from node to node - it is formed by Schwann cells in the PNS and olgidendrocytes in the CNS
What is the importance of the myelin sheath?
without it conduction would be too slow and patchy loss/scarring of the myelin sheath causes abnormal conduction which will appear as white plaques on an MRI
What is the difference between white and grey matter in the spinal cord?
White matter surrounds the central H-shaped grey matter
White= myelinated axons
Grey= neuronal cell bodies
How is the white matter arranged?
Tracts= specific bundles of axon carrying specific information to a specific part of the brain or periphery- can be descending (from brain/brain stem to periphery) or ascending (sensory information from the periphery)
Describe the dorsal and ventral roots of the spinal cord.
Dorsal (posterior) root is sensory and the ventral (anterior) root is motor - motor= multipolar so cell body is in the ventral root of the spinal cord and the axon leaves through the ventral root into either the ventral or dorsal ramus
Describe the distribution of grey and white matter in the brain.
Grey matter is around the edge and surrounds the white matter but there are also collections of grey matter found in the cerebral hemispheres called nuclei
What are the types of glial cell?
CNS= astrocytes, microglia, ependymal cells, oligodendrocytes PNS= Schwann cells, satellite cells
What are astrocytes?
Most common glial cell, have a central nucleus and multiple feet-like processes called end-feet which surround synapses and capillaries and help in K+ buffering and maintaining the BBB
What’s are microglia?
the WBCs of the brain (as normal WBCs cannot cross the BBB)- phagocytosis and scar tissue formation
What are ependymal cells?
Have a single process which projects upwards, they line the ventricles and central canal of the spinal cord
What are oligodendrocytes and Schwann cells?
Oligodendrocytes= myelination in the CNS
Schwann cells= myelination in the PNS
What are satellite cells?
Found in the neuronal cell bodies in ganglia and probably help in protecting the neuronal cell bodies in the ganglia
What is the blood brain barrier?
a barrier created between blood flowing through the capillaries and the brain tissue surrounding these capillaries = protective mechanism that helps maintain a stable environment for the brain and prevents harmful amino acids and ions present in the bloodstream and blood cells from entering the brain
What can cross the BBB?
Only lipid molecules or substances can move freely across the capillaries and water soluble molecules like glucose and AA need to pass through pumps
Where is the BBB absent?
in a few ‘circumventricular’ organs= parts of the hypothalamus and posterior pituitary are they are endocrine organs so this would impair their function
What do drugs to manage conditions in the brain need to be?
lipid soluble or use suitable vectors in order to get past the BBB
Describe the folds of dura matter which separate the brain.
falx cerebri= separates the 2 cerebral hemispheres
falx cerebelli= separates the 2 cerebellar hemispheres
tentorium cerebelli= separates the cerebral hemispheres from the cerebellum
What are ventricles and describe their locations.
cavities within the brain containing CSF and are all connected:
lateral ventricles= c-shaped cavities which lie in the cerebral hemispheres
interventricular foremen= connects the lateral to the 3rd ventricles which is in the diencephalon
cerebral aqueduct= lies in the midbrain
4th ventricle= diamond-shaped and lies in the hindbrain
What is CSF?
fluid inside the brain in the ventricles and central canal of the spinal cord and between the pia and arachnoid layers of the meninges - it is important for helping the brain float to prevent the cranial cavity from crushing itself with its own weight
Describe the circulation of the CSF.
formed in the choroid plexus inside each ventricle (mostly lateral) then goes to the 3rd and 4th and a little to the central canal but most enters the subarachnoid space - it is absorbed by arachnoid villi into the sagittal sinus
What are the meninges?
3 coverings of the CNS:
dura matter= tough, fibrous and has dural folds
arachnoid matte= middle layer
pia matter= vascularises and dips into folds of the brain
subdural space= potential space which is transverse by blood vessels penetrating into the CNS
subarachnoid space= contains CSF
