Question

During the conduction of an impulse inside the plasma membrane of a neuron, electrical potential changes from

• A. -ve to +ve and remains +ve
• B. -ve to +ve and then to -ve
• C. +ve to -ve and then remains -ve
• D. +ve to -ve and then to +ve

Answer 1

The correct option is B -ve to +ve and then to -ve

The concentration of $K^{+}$ ions inside cell is about 10 times that in the extracellular fluid, whereas the concentrations of $N{a}^{+}$ and $C{l}^{-}$ ions are much higher outside the cell than inside. The resting potential (inside negative) is determined mainly by the movement of $K^{+}$ ions. Movement of a $K^{+}$ ion across the membrane down its concentration gradient leaves an excess negative charge on the cytosolic face and deposits a positive one on the exoplasmic face.

At the beginning of the action potential, the $N{a}^{+}$ channels open and $N{a}^{+}$ moves into the axon, causing depolarization.

Repolarization occurs when the $K^{+}$ channels open and $K^{+}$ moves out of the axon. This creates a change in polarity between the outside of the cell and the inside.