Tissue ependymal cells cube shaped cells that produce

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Unformatted text preview: re brain surface & nonsynaptic Branched areas of gray matter areas • Extensions help form tight junctions btw neurons & Extensions endothelial cells of capillaries (bld-brain barrier) endothelial • Convert bld-glucose to lactate for nourishment, secrete Convert growth factors, regulate chemical composition, form scar tissue, etc. tissue, Ependymal cells= cube-shaped cells that produce CSF & help cube-shaped circulate it (via cilia) circulate Microglia= macrophages that wander CNS to phagocytize macrophages dead n.tissue, microorganisms, foreign matter dead • Help id sites of damage/infection since cluster in those areas Myelin Sheath Myelin Schwann cells= envelop fibers of PNS, winds around to form envelop myelin sheath; also helps in regeneration of damaged fibers myelin Satellite cells= surround cell bodies in ganglia (func unknown) Myelin= plasma membranes of glial cells (20% protein, 80% plasma lipids) form insulating sheath • Myelination of nervous system begins ~14th wk fetal Myelination system development, but not in brain @ birth development, • Process continues until late adolescence, but dietary fat Process needed most during early development needed • Oligodendrocytes (CNS) repeatedly wrap its p.membrane around adjacent fibers to form compact layers of myelin sheath sheath • Many oligodendrocytes are responsible for covering 1 axon • Schwann cells (PNS) spiral around a single fiber • Neurilemma= outer layer of sheath containing nucleus, cytoplasm outer Conduction Speed Conduction Basal lamina= surrounds myelin sheath; thin fibrous layer surrounds forms outermost layer (endoneurium) forms Nodes of Ranvier= gaps btw myelin segments • Internodes= myelinated seg’s Trigger zone= axon hillock + initial segment (btw a.h. & 1st glial cell); region important in initiating nerve impulse in Unmyelinated fibers occur in CNS & PNS; in PNS, schwann cells house 1-12 fibers & p.membrane folds over each once cells Conduction speed of nerve signal depends on 2 factors: • • • • Diameter of fiber & presence of myelin sheath Conduction occurs @ surface of fiber…more surface area .5-2 m/sec (unmyelinated) –vs- 3-15 m/sec...
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This note was uploaded on 01/12/2014 for the course ZOO 250 taught by Professor Staff during the Fall '08 term at S.E. Louisiana.

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