Nerve cells are called excitable cells because the potential difference across their membrane changes when they receive the stimulus and a wave of depolarisation or impulse passes from one end to the other.
Special features of membrane of neuron are
(i) They have ${{Na}^{+}}$ - ${{K}^{+}}$ pump which is active during the resting stage.
(ii) Voltage gated ${{Na}^{+}}$ and ${{K}^{+}}$ channels. ${{Na}^{+}}$ channels are densely clustered in the area called trigger zone, where stimulus is normally received.