DEOLARISATION :
Membrane potential becomes more positive. Causes Na+ channels to open, allowing Na+ influx into the cell.
REPOLARISATION AND HYPERPOLARISATION :
Membrane becomes more negative.
- R : From the maximum depolarized value back to RMP.
- H : From RMP to a more negative potential.
K+ channels open, allowing K+ efflux out of the cell.

An action potential is a temporary maximum depolarisation which propagates along the axons. It occurs when a local depolarisation reaches threshold potential (59mV)

ABSOLUTE :

• From the maximum depolarised value to the period of hyperpolrisation. Another action potential is not possible because the Na+ channels are unresponsive.

RELATIVE :

• From the period of hyperpolarisation back to the Resting membrane potential. Na+ channels are responsive but it is harder to generate another action potential because the membrane is hyperpolarised.