How do nerves transmit impulses Why is it that a myelin shea

How do nerves transmit impulses? Why is it that a myelin sheath increases the rate at which impulses are transmitted along a nerve? Please explain. 100 words or more please

Solution

During the resting state, the nerve cell is polarised. The interior of the cell is negatively charged, and it contains high concentrations of K⁺ ions. The exterior of the cell is positively charged, and it contains high concentrations of sodium ions. The resting membrane potential of a neuron is, -70 to -80mV (millivolts).

When any form of impulse strikes the nerve cell, it causes change in membrane potential by changing the ion permeability across the membrane. If the membrane potential reach threshold potential (the minimum potential difference to elicit a response), then the action potential is generated. The action potential is ten transmitted through an axon by means of influx and efflux of ions.

Myelin sheath is the lipid covering of the axons, which protect the axon and speed up the process of impulse conduction. Neurons with myelin sheath are called as myelinated neurons and neurons without myelin sheath are called as non myelinated neurons.

The gap junctions found at regular intervals in the myelin sheath are called as Nodes of Ranveir.   Myelin sheath does not allow the exchange of ions through it and exchange of ions occurs at Nodes of Ranveir only. Myelin sheath helps in the faster conduction of impulses through the axons by saltatory conduction (impulses jump from one node to another).

Thus, the impulses are conducted faster in myelinated neurons (glial cells insulate the neurons with myelin sheath) than non-myelinated neurons. In non myelinated neurons, the ions move through the axon length, so the conduction is slower.