Question

In nerve impulse conduction, the repolarization occurs with the

• A. efflux of $K^{+}$ ions
• B. influx of $K^{+}$ ions
• C. efflux of $Na^{+}$ ions
• D. efflux of both $Na^{+}$ and $K^{+}$ ions

Answer 1

Answer: (A)

Repolarization of a nerve is a process in which the negative resting membrane potential of a neuron is regained. Right after the depolarization of an action potential (where the membrane potential is positive), there is a change in the charge of the membrane potential which turns it into negative. This process is called repolarization.
During action potential, the sodium ions (Na⁺) channels open and the Na⁺ ions rush in. The sodium ions, being positively charged, increase the concentration of the positive charge in the inside of the axon. As the rapid influx of sodium ions takes place, the rising phase slows down and comes to a standstill as the sodium ion channels become completely open. When this process reaches it’s completion, the sodium pump stops working.
After the action potential takes place, which is generated by the influx of Na+, there is a period of repolarization wherein the sodium channels close and the potassium channels are activated.
Because of the efflux of potassium (K⁺) ions, there is a fall in the action potential phase. Initially, there is hyperpolarization followed by a phase called afterhyperpolarization wherein there is attainment of a membrane potential which is more negative than the resting potential. In repolarization the cells undergo a decrease in the voltage because of the efflux of (K⁺) ions.