NMJ Electrophys and Nerve growth Flashcards
describe a growth cone in 2 sentences
expansion on the tip of axon that senses environment. dictates growth via cytoskeletal remodeling in response to trophic factors.
ensure survival of neuron once proper synapse has been made
neurotrophins
3 things trophic interactions are responsible for
1) matching neurons to available target space 2) regulating the degree of innervation of individual afferents and their postsynaptic partners 3) modulating growth and shape of axon and dendritic branches
explain the neural response to botox administration (once vesicle fusion is blocked resulting in denervation); use trophic and muscle in your answer
in response to trophic factors produced by now denervated muscles, nerves try to re-inervate the muscle therefore they sprout terminal branches
flexing all toes in response to …..
stroking of lateral aspect of plantar foot
babinski reflex:
dorsiflexion of big toe and slight fanning of the toes upon plantar stroking of foot.
babinski normal in ages
normal up to 2 yrs old
in adults babinski indicates (less than sentence)
UMN lesion
describe wallerian degeneration in terms of response to …., and what part of …. is affected
response to cut or crush, distal parts of PNS axon degenerate
what two cell types cause breaking down of axon and myelin
proliferating schwann cells, and macrophages
describe retrograde degeneration using terms: weeks, cell body, and schwann cells
within 1-2 weeks of injury, proximal to cut, cell body swells and nissl bodies disperse, dendrites may be replaced by schwann cells
what are two (either or) requirements for regeneration?
endoneurial sheath intact OR severed nerves <2mm away
saturday night palsy is example of … type of injury via mechanism of ….
neuropraxia via temporary interference with fxn but no degen (e.g transient sustained pressure)
axonotmesis and mechanism
nerve injury where axon damaged but endoneurial sheath and schwann cells are fine; crush/ischemia
neurotmesis
nerve injury where axon and sheath and myelin are severed
what is first sign of regeneration of neuron
the cell body’s nissl bodies structure recovers
explain role of schwann cells in neuron regeneration use words such as bridge, trophic, and surround
schwann cells proliferate and lose their myelin. they then surround the basal lamina of endoneurium and act as a bridge. They provide trophic support as well.
explain axon sprouting in context of regeneration of nerve contrast this with botox poisoning
axon makes numerous sprouts on proximal end of cut, that all advance. only one sprout ends up innervating the end organ botox the neuron isnt regenerating strictly, but is merely sprouting in response to the denervated muscle trophic factors
when more than one axon is injured, and if multiple axons enter an endoneurial tube during regeneration, what can happen?
the wrong neuron type can pair with the wrong end organ.
why is recovery better in nerves that all all sensory or all motor?
if things get scrambled, at least same type of neuron
what is a mechanism by which a neuroma can form?
during regeneration if some of the terminal sprouts escape the epineurial sheath they can get tangled up and form neuroma.
what surrounds individual nerve fascicles?
perineurium
what surrounds groups of fascicles?
epineurium
when is myelin put on the axon in terms of the regeneration process?
when it reaches target organ
