lecture4-11

lecture4-11 - Lecture 4 The Action Potential-restricted to...

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Unformatted text preview: Lecture 4 The Action Potential -restricted to excitable cells (nerve cells, muscle cells, some gland cells) • in this nerve cell there were three depolarizations. Two of them caused graded potential (failed initiations). BUT one of them depolarized the cell past a threshold point at which an ACTION POTENTIAL occurred. The action potential is a rapid reversal of membrane polarity from negative to positive. It all occurs in a few 1/1,000ths of a second. The action potential is the result of events occurring in specific ion channels in nerve cells. The ones important for understanding the action potential: 1. K + leak channels – always open 2. voltage-gated Na + channel . This one channel has two “gates” •fast gate that opens in response to depolarization •slow gate that closes in response to depolarization 3. voltage-gated K + channel . This channel has one gate. •slowly opens in response to depolarization E Na + E K + hyperpolarization •what causes depolarization? •what causes depolarization? •what causes hyperpolarization? http://www.blackwellpublishing.com/matthews/channel.html movie voltage gated Na + voltage gated K + Na + K + a b c d b. c. a. d. ion channels return to “a” configuration, as membrane repolarizes. Prepares for next action potential extracellular intracellular What is the threshold? when membrane depolarized two things happen: 1. K + fows out oF cell through leak channels (and voltage gated K+ channels) 2. voltage-gated Na + channels open aFterhyperpolarization •So Far we have seen how the actions oF the voltage gated Na + and K + channels account For the action potential, but.........
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lecture4-11 - Lecture 4 The Action Potential-restricted to...

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