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3.6 Organisms respond to changes in their internal and external environments
Quick questions on Nervous coordination and the nerve impulse: resting and action potentials - AQA A-Level Biology
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is structure of a myelinated motor neurone?Show answer
A motor neurone carries impulses from the central nervous system to an effector. It has a cell body (with the nucleus), many dendrites that receive impulses, and one long axon that carries the impulse to the effector. The axon is wrapped in a myelin sheath made by Schwann cells, with gaps called nodes of Ranvier between adjacent Schwann cells.
What is the all-or-nothing principle?Show answer
An action potential is all-or-nothing. If the stimulus reaches the threshold, a full action potential of the same size is always produced; if it does not reach threshold, no action potential occurs. A bigger stimulus does not make a bigger action potential; instead it increases the frequency of action potentials. This is how the nervous system codes stimulus strength.
What is the refractory period?Show answer
After an action potential there is a short refractory period during which the sodium channels are recovering and the membrane cannot be stimulated again. Its importance is:
What is q1?Show answer
Explain how the resting potential of about -70 mV is established and maintained. [4 marks]
What is q2?Show answer
Explain what is meant by the all-or-nothing principle and how stimulus strength is coded. [3 marks]
What is q3?Show answer
Explain why an action potential travels faster in a myelinated than a non-myelinated neurone. [3 marks]
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