Which has the highest speed of nerve impulse?

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

Given below is a diagram of a resting nerve fibre in a polarised state. Select the option which illustrates the correct distribution of $Na^{+}$ and $K^{+}$ ions along the membrane.

Give scientific reasons:
$(1)$ In an excited nerve fibre region,a positive charge is created inside the plasma membrane.
$(2)$ In some animals,the conduction of nerve impulses is saltatory.

The mineral necessary for nervous conduction is

During the conduction of a nerve impulse, electrical energy is generated. What is the source of this energy?