Action Potential Essay

Topics: Action potential, Electric charge, Neuron Pages: 3 (665 words) Published: August 11, 2011
Resting potential is the membrane potential when a neuron is not conducting any electrical impulse or signal. The resting potential is around -75 mV. During resting potential, the inside of the axon is negative


Action potential is a fleeting reversal of the membrane potential, caused by changes in permeability of the plasma membrane of neuron to potassium and sodium ions causing an electrical impulse to be transmitted along the axon.

When a stimulus depolarizes the membrane, a few of the voltage-gated sodium channels that are found in the neuronal plasma membrane open permitting sodium ions to pass through. Since there is much greater concentration of sodium ions outside the axon than inside, they diffuse in through the open sodium channels down their concentration gradient. This result in the relatively high concentrations of positively charged sodium ions inside the axon and makes it less negative inside that it was before. The continue diffusion of sodium ions into the axon depolarizes the membrane more and brings it closer to the threshold. When the potential across the membrane reach the threshold (about –55 mV), additional voltage-gated sodium channel open. When this happens, there is rapid and intense influx of sodium ions into the axon causing the inside of the axon swiftly continues to build up more positive charges, until the membrane potential reaches a potential of about +40 mV compared with the outside.

At this point, the sodium channels are temporary close and are inactivated, so the sodium ions stop diffusing into the axon. At the same time, the voltage-gated potassium channels open. Potassium ions therefore diffuse out of the axon, down their concentration gradient. The outward movement of potassium ions removes positive charge from inside the axon to the outside, thus beginning to return the potential difference to normal. This is called repolarisation or refractory period....
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