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Unformatted text preview: Ch. 9 The Nervous System: The Central Nervous System I) General Anatomy a) Glial Cells i) 90% of the CNS, support neurons ii) 5 types: Schwann, oligodendrocytes, microglia, ependymal, astrocytes iii) All glial cells release growth factors iv) Astrocytes most diverse of glial cells, help development of neural connections; some wrapped around synapses and modulate activity; can remove neurotransmitters from synaptic cleft; release transmitters that communicate with neurons; help maintain normal electrolyte composition of EC fluid v) Microglia protect the CNS from foreign matter through phagocytosis vi) Neurodegenerative diseases (1) MS results from the loss of myelin in the CNS because the immune system attacks oligodendrocytes (2) Alzheimers is caused by the loss of cholinergic neurons and replacement of those neurons with scar tissue called plaques (a) Astrocytes and microglia become overly active and release inflammatory chemicals that further degenerate the cholinergic neurons vii) Parkinsons involves the loss of dopaminergic neurons b) Physical Support of the CNS i) The outermost structures that protect the soft tissue of the CNS are the cranium (skull) and the vertebral column (around the spinal cord) ii) The meninges are three connective tissue membranes that separate the soft tissue of the CNS from the surrounding bone (1) Dura mater outermost, closest to the bone (2) Arachnoid mater no space b/ween dura and arachnoid (3) Pia mater right next to nervous tissue; separated from arachnoid mater by the subarachnoid space , which is filled with cerebrospinal fluid which is similar to plasma iii) The brain contains four cavities called ventricles ; two C-shaped lateral ventricles are connected to a midline third ventricle by the interventricular foramen ; the cerebral aqueduct connects the 3 rd vent to the 4 th vent, which is continuous with the central canal , a long cylindrical cavity that runs the length of the spinal cord (1) The lining of the ventricles is composed of glial cells called ependymal cells (2) The lining is also vascularized and forms a tissue called he choroid plexus , which consists of pia mater, capillaries, and ependymal cells and functions in synthesis of CSF iv) The CSF is only 125-150 mL, but because it is recycled 3 times a day the choroid produces 400-500 mL a day (1) as CSF is produced it circulates through the ventricular system and enters the subarachnoid space through openings in the 4 th vent where arachnoid villi reabsorb the CSF into venous blood (2) It acts as a shock absorber and provides essential nutrients to neurons and glial...
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- Spring '07