Mylin sheath is preasent in.........
Answers
Answer:
sheath is a greatly extended and modified plasma membrane wrapped around the nerve axon in a spiral fashion
Explanation:
Myelin is an electrical insulator; however, its function of facilitating conduction in axons has no exact analogy in electrical circuitry. In unmyelinated fibers, impulse conduction is propagated by local circuits of ion current that flow into the active region of the axonal membrane, through the axon and out through adjacent sections of the membrane (Fig. 4-1). These local circuits depolarize the adjacent piece of membrane in a continuous, sequential fashion. In myelinated axons, the excitable axonal membrane is exposed to the extracellular space only at the nodes of Ranvier; this is the location of sodium channels [2]. When the membrane at the node is excited, the local circuit generated cannot flow through the high-resistance sheath and, therefore, flows out through and depolarizes the membrane at the next node, which might be 1 mm or farther away The low capacitance of the sheath means that little energy is required to depolarize the remaining membrane between the nodes, which results in local circuit spreading at an increased speed. Active excitation of the axonal membrane jumps from node to node; this form of impulse propagation is called saltatory conduction.