►Ensure one way transmission of nerve impulse ►Nerve impulse conduction is always unidirectional ►Means of communication between neurons or nerves and muscles.Īn axon stimulated in centre will conduct nerve impulse in both the directions. Propagates along nerve fiber as nerve signal or nerve impulse Propagation (conduction) of action potential Procaine, Tetracaine etc block voltage gated Na +channels, thus ►Action potential is the basis of following clinical investigations ►Action potentials can not be summated Clinical implications ►Absolutely refractory period of large myelinated nerve fiber is 0.4 ms, therefore, frequency of action potential is 2500/second ►Longer the refractory period, less will be the frequency ►Some voltage gated Na +channels regain their resting configuration ►From end of initial 1/3 of repolarization to start of after depolarization (middle 1/3rd) ![]() Period during which 2nd action potential can be generated but with stronger than normally required stimulus. It is mostly of 0.4 ms in large myelinated nerve fibers. ►After closure, the inactivation gates do not reopen until RMP is restored ►From start of depolarization to initial 1/3 of repolarization Period during which a 2nd action potential can not be generated. Na + -K +pump re-establishes ionic gradients (recharges the nerve fiber) Refractory period ►Too less amount of K +(due to massive K + efflux) ►Large amount of Na +(due to massive Na +influx) ► Subthreshold stimulus will not elicit action potentialĭuring action potential Na +& K +ionic gradients reverse. ► Suprathreshold stimulus will elicit same action potential as elicited by threshold stimulus ►Action potential will either be generated or not…no gradations or intensities or possible ►Na + -K +pump restores RMP from hyperpolarization ►Potential decreased more than resting level ►Some voltage gated K +channels remain open even after RMP (-90 mv) is restored ►Voltage rises and crosses zero (overshoot) ►About 5000 fold increase in Na +permeability Opening of ligand gated Na + channels (chemical stimulus) Opening of mechanically gated Na +channels (mechanical stimulus)ģ. Opening of voltage gated Na +channels (electrical stimulus)Ģ. These are the cells with the capability to generate action potentials, mostly are the nerve and muscle cellsġ. Now let us consider action potential which occurs only in the excitable cells. ►Remains open till resting membrane potential is is restored ►Activation gate remains open Voltage gated K +channels: ►Inactivation gate starts closing -slow process Voltage gated K +channels Voltage gated Na +channels: When the cell is at rest, cell membrane is negatively charged (polarized) from inside as compared to outside Voltage gated channels:Ģ. ![]() We know that cell is electrically neutral. Brief, rapid, large and reversible change in resting membrane potential of an excitable cell during which the membrane potential reverses (cell inside becomes more positive than outside) is known as action potential.īefore considering action potential, we must familiarize ourselves with the potential in the cell in resting state.
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