6.2.4 The Refractory Period

Key Features of the Refractory Period

1. Phases of the Refractory Period:

• Absolute Refractory Period:
• During this phase, no action potential can be generated, regardless of the strength of the stimulus.
• This occurs because the sodium ion channels remain closed, preventing depolarisation.
• Relative Refractory Period:
• During this phase, a new action potential can be generated, but only if the stimulus is much stronger than usual.
• This is because the membrane is still hyperpolarised.

2. Functions of the Refractory Period:

• Ensures that action potentials travel in one direction only by preventing the propagation of a backward impulse.
• Produces discrete impulses by ensuring that each action potential is separate from the next.
• Limits the frequency of nerve impulses, ensuring the neurone has time to recover.

3. The All-or-Nothing Principle:

• An action potential is only generated if the stimulus reaches a threshold value.
• If the threshold is not reached, no action potential is produced.
• All action potentials generated have the same magnitude, regardless of stimulus strength.