BRAINCAKERefractory Period
After an action potential there is a short time during which the axon membrane cannot be stimulated to produce another action potential, or can only be stimulated by a much stronger stimulus. This is the refractory period. It lasts a few milliseconds and has two parts.
Absolute refractory period (about 1 ms): the voltage-gated sodium ion channels are inactivated after depolarisation. They cannot open again until the membrane has repolarised, so no stimulus, however strong, can produce a new action potential.
Relative refractory period: the Na+ channels have recovered, but the membrane is still hyperpolarised because some K+ channels are still open. A new action potential can be produced, but only by a stimulus stronger than normal.
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More in Mammalian Nervous System
- Action Potential
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Transmission of Nerve Impulses
- Saltatory Conduction
- Synapses
- Pre-synaptic Membrane
All 38 lessons in Mammalian Nervous System · All Edexcel A-level Biology topics