Myelinated nerve fibers

Myelinated Nerve Fibers

A myelinated neuron from a chicken. Image courtesy of Wikimedia Commons.

Myelinated nerve fibers are neurons that are covered with a protective sheath called myelin. This sheath is made up of layers of a fatty substance that insulates the nerve fibers and increases the speed at which electrical impulses, or action potentials, are conducted along the nerve fiber.

Structure

Myelinated nerve fibers consist of a axon, which is the long, slender projection of a nerve cell, and the myelin sheath, which covers the axon. The myelin sheath is made up of Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. The myelin sheath is not continuous along the length of the axon; there are small gaps known as nodes of Ranvier, where the axon is exposed.

File:Myelin sheath.jpg

Diagram of a myelinated axon. Image courtesy of Wikimedia Commons.

Function

The primary function of myelinated nerve fibers is to increase the speed of electrical impulses along the nerve fiber. This is achieved by a process known as saltatory conduction, where the electrical impulse jumps from one node of Ranvier to the next, rather than traveling along the entire length of the axon.

Clinical significance

Damage to the myelin sheath, as seen in diseases such as multiple sclerosis, can lead to a decrease in the speed of electrical impulses, resulting in a variety of neurological symptoms.

See also

• Neuron
• Myelin
• Schwann cell
• Oligodendrocyte
• Node of Ranvier
• Saltatory conduction
• Multiple sclerosis