BRAINCAKEDepolarisation
Depolarisation is the change in the potential difference across a neurone membrane from its resting value (about −70 mV) towards zero and then above it, as the inside of the axon becomes less negative and then positive.
At rest, the voltage-gated sodium ion channels in the axon membrane are closed. Na+ is at a much higher concentration outside the axon, and the inside is negative, so there is a steep electrochemical gradient for Na+ to enter.
When a stimulus arrives, for example at a receptor or as a local current from an adjacent part of the axon, it opens some Na+ channels. Na+ ions diffuse into the axon, making the inside less negative.
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Key terms in this lesson
- positive feedback
- A response that increases a change in a variable, moving it further from its starting value.
More in Mammalian Nervous System
- Speed of Nerve Impulses
- Investigating Nerve Impulses
- Resting Potential
- Action Potential
- Repolarisation
- Hyperpolarisation
- Refractory Period
- Transmission of Nerve Impulses
All 38 lessons in Mammalian Nervous System · All Edexcel A-level Biology topics