Speed of the Nerve Impulse

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An action potential travels down a neurone as a nerve impulse. The size of the action potential remains the same all the way along.

Factors affecting the speed of a nerve impulse

  • The myelin sheath. The myelin sheath that forms around a neurone acts as an electrical insulator, stopping an action potentials forming on the surface of the neurone. It is only at regular breaks in the myelin sheath, called the nodes ranvier, where action potentials can form, and the impulse will jump from node to node by saltatory conduction. This can increase the speed of the impulse from 30ms-1 to 90ms-1.
  • Axon diameter. The larger the diameter of the axon, the faster the speed of conductance down the axon. This is due to less ions leaking out of the axon. Ion leakage can make membrane potentials harder to maintain.
  • Temperature. Temperature affects the rate of diffusion of sodium and potassium ions across the membrane. The higher the temperature, the faster ions diffuse, the faster the axon membrane becomes depolarised and the faster the nerve impulse travels. In restoring and maintaining resting potentials, ATP is required to operate the sodium-potassium pumps. This ATP comes from respiration, and like most biochemical processes, it is catalysed by enzymes, which work faster at higher temperatures.Above a certain temperature…


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