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Axon Facts
- Points along axon don't have same meb pot (unlike soma- which does)
- suprathresh- losslessness :)
- Larger diam= lower R-> subthresh V goes further and can conduct AP at higher velocity
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Myelination
- Inc R at myelin-> depol forward rather than leak out
- R at nodes is low, g is high= LOTS of Na channels at nodes
- **Dec Capacitance= less charge needed to get Ap; faster change in memb potential
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Recruitment
Normally: smallest-> largest axonsArtif stim: largest-> smallest (largest axons have lower thresh); "inverse rank"; a challenge to prosthetics
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SNAP- Sensory nerve AP
- over tendons
- conduction study:
- latency (conduction velocity), duration, amplitude
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CMAP- Compound m AP
- over m... synch stim swamps out sens n
- motor conduction study also: latency, duration, amplitude
- Sensory- IA fibers, large n, low thresh-> H first
- Inc intensity- M- othodromic
- motor goes both way- cancels H
- F- antidrom richasaying
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Peripheral Neuropathy
- caused by demyelination or axonal defect
- demyelination- conduction study of SNAP/CMAP-> slowed latency (conduction velocity), temperal dispersion (inc duration and dec ampl)
- axonal- dec ampl, w/o prolonged latency
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Peripheral Neuropathy
- caused by demyelination or axonal defect
- demyelination- conduction study of SNAP/CMAP-> slowed latency (conduction velocity), temperal dispersion (inc duration and dec ampl), conduction block
- axonal- dec ampl, w/o prolonged latency
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Peripheral nerve damage
- Mild- neuropraxis
- Crush- axonotmesis- axon damaged but basal lamina fine; Wallerian degeneration; regrowth 1mm/day helped with neurotrphins to maintain connections
- Cut- neurotmesis- all damaged; regeneration poor
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CNS damage
little regeneration because of glial scar and inhibitory factor
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