Question

Describe the two stages of the Action Potential. Include (i) the names of the ion channels and whether they are active or passive, (ii) which of these ion channels open during the first stage and which open during the second stage, and the direction ions move, and (iii) the value in mV reached during the two stages.

Answer 1

Action potential is defined as the change of the resting membrane potential. It occurs when a neuron sends information down an axon, away from the cell body.Two stages of Action Potential included depolarization and repolarization.

Depolarization is also known as the rising phase. This is caused when when positively charged sodium ions (Na+) rush through open voltage-gated sodium channels into a neuron. As sodium goes in, the polarity of the membrane potential is reversed to a positive value of 40mV.

Repolarization is also called as the falling phase and is caused by the closing of the sodium channels and opening of the potassium channels. Ths, the membrane permiability to sodium ions decline leading to the rushing of potassium ions out of the cell. This restores the localized negative membrane potential of the cell. The negative potential is close to -75mV.

(i) The sudden shift from resting state to active state is causeby the movement of ions accross the membrane into the cell. Therefore, the active state is when the sodium ions enter into the cell. Thus, the pottassium channels are passive.

(ii) During the first stage ( depolarization stage), the sodium channels are open. Whereas, during the second stage, the sodium channels close and the potassium channels open up.

(iii) Action potential begins when depolarization increases the membrane voltage to cross a threshold value of around -55mV. During the depolarization stage, influx of sodium ions makes the membrane potential increase very rapidly, going all the way up to about +40mV.