Depolarization of a stimulated nerve is maintained by

The potential difference across the membrane of a relaxed muscle fibre is called resting potential. It amounts to about

When a neuron is in resting state $I$ not conducting any impulse,the axonal membrane is :

During the propagation of a nerve impulse,the action potential results from the movement of

Assertion $(A)$: The axonal membrane of the neuron is more permeable to sodium ion $(Na^+)$ and nearly impermeable to potassium $(K^+)$.
Reason $(R)$: In a resting state,a neuron does not conduct any impulse.

Maintenance of the ionic gradients across the resting membrane is done by the