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Nervous Transmission

Human Biology (Year 12)

Transmission of a Nerve Impulse

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Ben Whitten

How does myelinated and unmyelinated transmission work?

In comparison to unmyelinated nerve fibres, myelinated nerve fibres are generally longer and therefore they require nerve impulses to travel faster to meet the needs of the organism. A myelinated nerve fibre has a myelin sheath wrapped around its axon, produced by Schwann cells; it is a fatty, white substance which has key roles in nervous transmission. The myelin sheath insulates the nerve fibre, except at the Nodes of Ranvier, and this prevents the flow of ions and stops the action potential from being formed; to combat this, the action potential jumps from one Node of Ranvier to the next node, in a process termed saltatory conduction, which increases the speed of transmission. Unmyelinated fibres are much slower in comparison to myelinated fibres as they lack a myelin sheath, and hence the nerve impulse is not insulated. The relative speeds of transmission are 140m/s for myelinated fibres and 2m/s for unmyelinated fibres.


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