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Med Neuro Lect3
Med Neuro Lect3 Neuronal Mechanisms Part 2
Question | Answer |
---|---|
What accounts for 90% of the cells in the CNS? what are the 3 main types? | GLIAL CELLS. 1.Astrocytes (protoplasmic and fibrous). 2.Oligodendrocytes. 3.Microglial cells. **all 3 aid in development and maintenance of neurons & Synapses. |
3 main functions of Astrocytes (50% of cells in the CNS) | 1.Metabolic compartmentation. 2.Synaptogenesis. 3.Tissue Repair (gliosis). **Form the BBB and traffic nutrients and waste in and out of neuronal somas (compartmentalize & protect brain). |
What is Gliosis? | Proliferation of astrocytes which forms glial scars. **Can be hamrful. |
Is the neuronal cell membrane exposed to the extracellular? | NO, it is MOSTLY covered by end feet of astrocytes, the rest are locations of Axosomatic synapses. |
When might you see a fibrous gliosis? | After a stroke |
Are Oligodendrocytes limited to supporting only ONE axon like Schwann cells are? | NO, they can wrap/myelinate and support multiple axons at a time. |
Describe the myelin sheath that the Oligodendrocytes wrap around axons | Flat (until axon is rolled up in it), protein and lipid rich. **Therefore viral infections can trigger an immune response which could then target the myelin (MS in CNS, Guillian Barret in PNS) |
Corpus Callosum | Heavily myelinated bridge b/w right and left hemispheres of the brain (will appear very white due all myelination). **Will see plaques there with MS due to overactive microglial cells. |
What are Astrocytes and Oligodendrocytes derived from? | Ectoderm. |
What are Microglial cells derived from? | Monocytes that have migrated out of the BL into the brain. |
What will cause a proliferation of Microglial cells? what is their function? | Damage to the brain, or to the BBB (allows more macrophages to migrate out of the BL). **They Phagocytize the damaged neurons (serve as the immune system of the brian). |
What CNS cells are responsible for producing Cytokines? name the 4 it produces | MICROGLIAL CELLS: 1.Interleukin-1. 2.Interleukin-6. 3.Tumor necrosis factor. 4.Transforming growth factor. |
3 types of cells lining the brain | 1.Ependymal cells (line the ventricles). 2.Choroid plexus (proliferating ependymal cells that produce CSF by acting like a glomerulus found in EACH ventricle). 3.Pial cells (flattened cells lining entire brain minus ventricles). |
Since the brain is protected by BBB and linings, how do hormones and ions reach the BL from the Hypothalamus? | Ependymal cells. |
What connects the 2 lateral ventricles? | Interventricular foramen. |
Where does the 3rd ventricle lie? what connects it to the 4th ventricle? | MIDLINE. **The cerebral aquaduct connects it to the 4th. |
Where does the CSF go from the 4th ventricle? | It drains into the subarachnoid space via 3 foramina (2 lateral, 1 medial). |
Is there a choroid plexus in every ventricle? | YES. The CSF it prodcues only circulates b/w the ventricles and subarachnoid space. |
Is CSF production under neurogenic control? if so, what Inc or Dec production? | YES. **SNS adrenergic system DEC production. **PNS cholinergic system INC production (by 2X). |
How much CSF is produced per day and what drives its movement? | 500-600mL per day (40% is extruded off ventricular wall). **Movement results from a hydrostatic gradient between ventricles and venous channels. Ventricular pressure can be 180 mm of water while that of the superior sagittal sinus is 90 mm of water |
2 ways CSF drains from the subarachnoid space | 1.Subarachnoid granules of superior sagittal sinus. 2.Spinal granulations of spinal nerves. |
2 main functions of CSF | 1.Waste removal. 2.Helps brain combat gravity by providing a floating material. |
Hydrocephalus | Imbalance b/w CSF prduction and drainage which leads to a build up of CSF from: 1.Overproduction. 2.Occlusion/blockage. **Very Destructive. |
What occurs in hydrocephalus as a result of the build up of CSF? | Brain becomes erroded. |
What does hydrocephalus sometimes follow? (due to the increased dead brain tissue draining into the CSF and clogging the drainage pathways) | STROKE (will develope rapidly afterwards if this occurs). |