Why is Myelin Important

Neurons carry messages using a chemical version of electricity. The outer surface of all types of cells is called the membrane. The axons of neurons have special membranes that maintain a difference in the balance of positive and negative charges across the membrane, like a battery. The charge of a neuron's battery is based on the number of sodium (Na+) and potassium (K+) ions inside and outside the membrane. Messages are carried, or conducted, along axons and dendrites by the change in electrical charge across the membrane.

An 'action potential' is the name for an electrical message carried along the axon or dendrite of a neuron, like an electrical impulse carried along a wire. These tiny electrical signals would not be able to travel very far if the axons were not insulated. Once this electrical charge or 'action potential' reaches the synapse, it triggers neurotransmitter release to enable the signal to reach the next neuron in the chain.

A wire carries electricity both faster and farther when it is. The longer the wire is, the more important the insulation is for efficient conduction. The same thing is true for axons and action potentials that travel down them. An action potential is triggered within the cell body of the neuron after the neuron receives signals from other neurons (see Neurotransmission). The insulation around axons is provided by a protein covering called myelin. In the brain and spinal cord, myelin is made by oligodendrocytes. The myelin wraps around each axon in many layers. Axon fibers insulated by myelin can carry action potentials at a speed of 100 meters per second, while axon fibers without myelin can only carry action potentials at a speed of 1 meter per second.

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