Neural Tissue - Transmission and Generation of Nerve Impulse

The polarised state is when the outer side of a nerve fibre carries a positive charge due to more Na⁺ ions outside the axon membrane in the resting condition.

The sodium pump is a cellular mechanism that uses energy from ATP to actively transport sodium ions out of the axon, helping restore the resting state after depolarisation.

• Nerve impulse is unidirectional — received by dendrites → transmitted via axon to next neuron.
• Polarisation (Resting State) — Na⁺ high outside, K⁺ high inside. Inside = negative. Resting potential = −70 mV. Both Na⁺/K⁺ channels closed.
• Depolarisation (Action Potential) — Stimulus → Na⁺ channels open → Na⁺ rushes in → inside becomes positive.
• Repolarisation — Na⁺ influx stops → K⁺ flows out → inside becomes negative again → resting potential restored.
• Nerve impulse = wave of depolarisation along the neuron. During the refractory period, the nerve cannot respond to a new stimulus until repolarisation is complete.