PHGY 311 Chapter Notes - Chapter 7 + Appendix 1: Sodium Channel, Reversal Potential, Membrane Potential
23 Sep 2017
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Repolarization & refractory period: na+ channels have two gates that respond in opposite ways, activation gate (opened during depolarization, closed during repo) Inactivation gate (closed during depo and opened during repo: hyperpolarizing after-potential: due to delayed closing of k+ channels, refractory period is overall 5-10ms, absolute due to inactivation of na+ channels. Subthreshold depolarization: small subthreshold depolarization increases inwards na+ current, but also outward k+ current (increase in gk, but since k+ channels slower, reach point where have net inward sodium current. Excitability: calcium [c] modulates channel activity --may increase many folds unlike other ions with constant concentrations throughout, trigger zone has very high density of voltage-gated sodium channels, so has lowest threshold for. Ap: located at initial segment, ap at the end of axon triggers calcium influx which initiates neurotransmitter release. Appendix 1 - review of basic circuit theory. Charge on that plate: eventually stop flowing since electrons attracted back towards positively charged plate, q = c x v.
