Explain an action potential. Include triggering and all channels and flow of ions.

Solutions

Expert Solution

The 5 main phases of action potential include the following.

Phase 1: It is the resting membrane potential. During the resting state, the nerve cell is polarized. The interior of the cell is negatively charged, and it contains high concentrations of K+ ions. The exterior of the cell is positively charged, and it contains high concentrations of sodium ions. The resting membrane potential of a neuron is, -70 to -80mV (millivolts).

Phase 2: When any form of impulse strikes the nerve cell, it causes change in membrane potential by changing the ion permeability across the membrane. If the membrane potential reach threshold potential (the minimum potential difference to elicit a response), then the action potential is generated. The fast sodium channels open after reaching the threshold potential causing depolarization of the membrane (represented by sharp peak in the graph).

Phase 3: This is the end of or peak of depolarization. The membrane potential moves towards positive side, when the membrane potential becomes more positive inside i.e., approximately, +35 to +45Mv. The process of depolarization stops by the closure of sodium channels. This phase is followed by depolarization.

Phase 4: It is the efflux of potassium ions, and the membrane potential moves to the negative side. When it reaches normal resting membrane potential, the cell enters into the resting stage.

Phase 5: After repolarization, if the efflux of potassium ions continues, then the membrane potential become more negative inside, causing hyperpolarization of the cell.

Sydney Mullin answered 11 months ago

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