During a nerve impulse, sodium ions enter the axon, reversing the voltage and depolarizing the inside. This generates an action potential that travels down the axon. Potassium ions then shift the voltage negative again, returning the axon to its resting polarized state, ready to transmit another impulse if stimulated.

1. Transmission of nerve impulses

2. axon

3. During a nerve impulse
Na+
axon

4. During a nerve impulse
K+ Na+
axon

5. Resting state
More positive – outside
axon
Less positive - inside

6. During an action potential
Na+
axon
Less positive - inside

7. During an action potential
Na+
axon
Inside becomes DEPOLARISED

8. During an action potential
Na+
axon
Inside becomes DEPOLARISED
Action potential is generated