1986
214
Neural Control and Coordination
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Solution:
The fatty myelin sheath acts as a highly insulating covering that prevents the flow of ions between the fluid external to the sheath and the fluid within the axon. The ionic flow and reversed polarity occur only at the nodes of Ranvier, where the insulating myelin sheath is absent and the voltagegated ion channels are concentrated. Because the action potential jumps from node to node, transmission of impulse is more rapid in myelinated fibres. This is called the saltatory conduction of nerve impulse. Myelinated nerve fibres require less energy for action because only the nodes are depolarised and fewer ions are required to be pumped back into position by the energy-requiring active transport mechanism.