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Saltatory Conduction of Nerve Impulse in a Myelinated Nerve Fibre

Neurons possess axons with sheaths at intervals by Schwann cells. These are lipid-rich cells that envelop the axon by wrapping their plasma membrane around it many times to produce a series of layers called myelin sheaths. It acts as a biological electrical insulation creating a region of high electrical resistance on the axon. Schwann cells are not continuous but broken at certain intervals called nodes of Ranvier. These nodes are critical to the conduction of nerve impulse in the cells. These cells are called myelinated neurons. The myelinated neurons carry impulses about 20 times faster than non myelinated neurons. In myelinated nerve fibre, the myelin sheaths is impermeable to ions and therefore, it prevents the Ion exchange and depolarization of nerve fibre along the whole length of the nerve fibre. The ionic exchange and depolarization occur only at nodes of Ranvier where the insulating myelin sheath is absent. Since the action potential jumps from one node to another node, transmission of impulse is more rapid in myelinated neurons. This mode of transmission of nerve impulses in a jumping manner from one node to another is called saltatory conduction of nerve impulse. Saltatory conduction is responsible for the greater speed of an impulse travelling along a myelinated neuron than a non myelinated neuron. Myelinated neurons require less energy for action because only the nodes are depolarized and few ions are required to be pumped back into the position. Impulse conducted in this fashion moves very rapidly. In non-myelinated nerve fibres, the ionic flow and depolarization are repeated along the entire length of the fibre. Therefore, impulse conduction is slow in such fibres.