Anatomy Exam 4 - PNS(Part 1 Nerve Structure and...

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PNS (Part 1) Nerve Structure and Classification - Endoneurium ~ surrounds each individual neuron (axon + myelin sheath) -Perineurium ~ surrounds “fascicles” or bundles of neurons -Epineurium ~ surrounds bundles of fascicles -Nerves have many bundles of fascicles together -3 Types of neurons 1) Sensory ~ recognizes and sends information to integration center (CNS); afferent pathways 2) Motor ~ exits the spinal cord from ventral root and stimulates ventral organ (efferent pathways effector organ) 3) Mixed ~ both sensory and motor; spinal nerves (PNS) Regeneration of Nerve Fibers ~ can only be regenerated if you damage the axon, if you damage the cell body it cannot regenerate further from the cell body, you’re more likely to regenerate 1) Wallerian degeneration ~ process where everything distal from the injury site, fragments the distal part of the axon -Ex: smashing your finger and cut axon myelin damaged -Separated ends seal themselves off and swell as substances transported in the axon accumulate in the sealed ends 2) Macrophages ~ come in and clean up the mess -DO NOT phagocytize schwann cells, just everything else -Macrophages stimulate schwann cells to divide in order to make myelin 3) Regeneration tube ~ schwann cell makes a tube across the damaged axon, forces it to connect with the other side -Smaller damaged chunks are easier to repair -Axon inside regeneration tube grows 4) New myelin sheath ~ schwann cells then wrap around axon, creating new myelin sheath -New regenerated axon is thinner, due to being able to regenerate but not back to 100% -Nissl bodies ~ increased protein synthesis
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-When neuron is damaged, Nissl bodies go into overdrive producing proteins for growth, repair and regeneration - Chromatolysis ~ closing down of Nissl bodies in the cell body of a neuron *CNS (Oligodendrocytes and astrocytes) -Oligodendrocytes ~ secrete growth-inhibiting proteins—neurite outgrowth inhibitor (Nogo A) inhibits axonal regeneration -Astrocytes ~ form glial scar tissue rich in chondroitin sulfate proteoglycans + keratin sulfate proteoglycans -Blocks axonal regrowth *IF you have a lesion and don’t squish the neuron, you MAY be able to regenerate BUT not likely (shown in lab) *No regeneration in CNS, due to chemicals secreted by neuroglia (oligodendrocytes + astrocytes) Cranial Nerves (bilateral) -Anything in yellow (above) are cranial nerves -Some strictly sensory (I + II); some strictly motor and some are mixed -Cranial nerves serve only the head and neck structures—“vagus nerve” is the only one that extends to the abdomen -Ways to remember: -“ O oh, O oh, O oh, t o t ouch a nd f eel v ery g ood v elvet, A hh h eaven”—cranial nerves (Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory and hypoglossal) -“Some say marry money, but my brother believes big brains matter more”—what type of nerves (either sensory, motor, or both) -Sensory—cell bodies located in sensory organ -Vestibulocochlear nerve ~ inside the ear (for balance)
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