Which of the following represents a polarized nerve membrane?

$A$: Presence of myelin sheath increases the rate of conduction of nerve impulse.
$R$: Ionic channels are absent in the area covered by myelin sheath; therefore,depolarization occurs only at the nodes of Ranvier,resulting in saltatory or jumping conduction.

Identify the incorrect statement.

$A$: In the nervous system,the generation of an action potential depends upon the influx of sodium ions into the axoplasm.
$R$: The influx of sodium ions during nerve impulse generation is due to the efflux of potassium ions.

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.

If the inside of the membrane becomes more negative,it leads to: