During the transmission of nerve impulse through a nerve fibre, the potential on the inner side of the plasma membrane has which type of electric change?

• A

  first positive, then negative and continue to be negative
• B

  first negative, then positive and continue to be positive
• C

  first positive, then negative and again back to positive
• Correct answer
  D

  first negative, then positive and again back to negative.

Solution

The first channels to open are the sodium ion channels, which allow sodium ions to enter the cell. The resulting increase in positive charge inside the cell (up to about +40 $\mathrm{mV}$ ) starts the action potential. This is called the depolarization of the membrane. Potassium ion channels Related Theory Events that characterize the transmission of a nerve impulse. (Ref. to Fig. 25.7)

Hence, the correct answer is option: 'D'.