HN220 Lecture 8: HN220 Lecture 8 - Nervous & Electrical Signalling Part 3 - Winter 2019
Document Summary
Axonal na+ channels: given that na+ channels opened in response to depolarization, why do they clse when cell is still depolarized, na+ channels have two gates, 1. Activation gate: voltage dependent, opens at threshold and depolarization, positive feedback, 2. Inactivation gate: voltage and time dependent, opens during depolarization, closes during depolarization inactivation gates respond to depolarization but with a 0. 5 msec delay. Generation of ap: reurn to normal permeability, @ +30 mv, na+ inactivation channels close, k+ channels open, repolarization begins, after-hyperpolarization. Absolute refractory period: membrane cannot produce another ap because na+ channels are inactivated, ap cannot overlap, ensures 1 way travel of ap, cell body to axon terminal, limits the rate of spike frequency (rate coding) Relative refractory periods: follows absolute refractory period, occurs when k+ channels are open, making it harder to depolarize the threshold. Stimulus intensity is coding: high stimulus intensity fires more aps, size of aps remains constant, aps can"t sum.
