BIOL 2457 1st Edition Lecture 26Outline of Last Lecture Nervous Tissue Outline of Current LectureNervous Tissue Regeneration & Repair Plasticity maintained throughout life Sprouting of new dendrites Synthesis of new proteins Changes in synaptic contacts with other neurons Limited ability for regeneration (repair) PNS can repair damaged dendrites or axons CNS no repairs are possibleDamage & Repair in the Peripheral Nervous System When there is damage to an axon, usually there are changes, called chromatolysis, which occur in the cell body of the affected cell; this causes swelling of the cell body and peaks between 10 and 20 days after injury. By the third to fifth day, degeneration of the distal portion of the neuronal process and myelin sheath (Wallerian degeneration) occurs; afterward, macrophages phagocytize the remains. Retrograde degeneration of the proximal portion of the fiber extends only to the first neurofibral node. Regeneration follows chromatolysis; synthesis of RNA and protein accelerates, favoring rebuilding of the axon and often taking several months.Repair Within the PNS Axons & dendrites may be repaired if Neuron cell body remains intact Schwann cells remain active and form a tube Scar tissue does not form too rapidly Chromatolysis 24-48 hours after injury, Nissl bodies break up into fine granular massesRepair Within the PNS By 3-5 days, Wallerian degeneration occurs (breakdown of axon & myelin sheath distal to injury) Retrograde degeneration occurs back one node Within several months, regeneration occurs Neurolemma on each side of injury repairs tube (schwann cell mitosis) Axonal buds grow down the tube to reconnect (1.5 mm per day)Neurogenesis in the CNS Formation of new neurons from stem cells was not thought to occur in humans There is a lack of neurogenesis in other regions of the brain and spinal cord. Factors preventing neurogenesis in CNS Inhibition by neuroglial cells Absence of growth stimulating factors Lack of neurolemmas Rapid formation of scar
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