Define nerve impulse and explain its conduction in a nerve fibre

Nerve impulse : Nerve impulse is any signal initiated by the stimulus at the receptor. Nerve cells are excitable.
Conduction of Nerve Impulse in Non-Myelinated Nerve Fibre : It is divided into three phases :
(a) Resting phase : During this phase, there is more Na+ ions on outside of axon membrane in ECF than inside of the axon membrane. K+ ions move out and the membrane is positively charged outside and negatively charged inside. This membrane is in resting potential (-80mV).
(b) Action Potential: It is other name of nerve impulse with resting potential. When the stimulus is applied the axon membrane is negatively charged outside and positively charged inside. It is called
depolarized or an action potential (+30 mV). The s electrogenic pump expels three Na+ for every two
K+ imported. Na+ K+ ions transmembrane pumps
are very important in membrane potential.
© Recovery Phase : During this phase depolarized
point becomes repolarized and Na+ ions move to
outside while K+ ions move inside.