OCR A Level Biology

Revision Notes

5.3.6 The Refractory Period

The Refractory Period

  • After the action potential, there is a period of time when both sodium ion channels are closed (during repolarisation) and potassium ion channels are closed (during hyperpolarisation).
  • When this occurs, this section of the axon membrane is in a period of recovery and is unresponsive
  • This is known as the refractory period

Action potential graph, downloadable AS & A Level Biology revision notes

The refractory period begins when repolarisation starts and ends when the resting state is reestablished.

The importance of the refractory period

  • The refractory period is important for the following reasons:
    • It ensures that action potentials are discrete events, stopping them from merging into one another
    • It ensures that ‘new’ action potentials are generated ahead (ie. further along the axon), rather than behind the original action potential, as the region behind is ‘recovering’ from the action potential that has just occurred
    • As a result, an impulse can only travel in one direction, which is essential for the successful and efficient transmission of nerve impulses along neurones
    • The existence of the refractory period also means that there is a minimum time between action potentials occurring at any one place along a neurone
    • The length of the refractory period is key in determining the maximum frequency at which impulses can be transmitted along neurones (between 500 and 1000 per second)

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