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50 mV

50 mV. 10 ms. depol n. repol n. 50 mV. 1 ms. hyperpol n. repol n. 50 mV. 2 ms. [K + ] o [K + ] i. A. extracellular intracellular. [Na] 145 mM 10 mM [K] 4.5 mM 140 mM. -. Nernst equation for a permeable ion (e.g.K + )

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50 mV

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  1. 50 mV 10 ms depoln repoln 50 mV 1 ms hyperpoln repoln 50 mV 2 ms

  2. [K+]o [K+]i A extracellular intracellular [Na] 145 mM 10 mM [K] 4.5 mM 140 mM - Nernst equation for a permeable ion (e.g.K+) Em (mV) = 61 log10 Assume K+ is permeable EK = 61 log10 EK = -92 mV Assume Na+ is permeable ENa = 61 log10 ENa = +71 mV 4.5 140 145 10

  3. B ENa Na+ influx K+ efflux g, mS.cm-2 +20 0 -70 40 30 20 10 0 action potential gNa Em mV gK 0.5 ms EK EK

  4. 0 mV 50 mV 1 ms Absolute refractory period Relative refractory period relative stimulus strength

  5. - - - - - - - - - - - - - - - - - - 50 mV cytoplasm 1 ms - - - - - - - - - - - - - - - - - - - - - + + + - - - - - - - - - - - - action potential cytoplasm - - - + + + - - - - - - - - - - - - - - - + + + - - - - - - - - - - - - action potential cytoplasm - - - + + + - - - - - - - - - - - - - - - - - - - + + + - - - - - - - - action potential cytoplasm - - - - - - - + + + - - - - - - - - cytoplasm - - - - - - - + + + - - - - - - - - action potential cytoplasm - - - - - - - + + + - - - - - - - - A i) ii) iii) iv) v)

  6. B axon myelin sheath axon node of Ranvier Action Potential + - - - - - - direction of propagation cyto- plasm + - - - - - - myelin

  7. A 50 mV AP AP subthreshold axon 2 mV Axon hillock/ Initial segment 10 ms B APs axon temporal summation + spatial summation

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