The Functions Of The Myelin Sheath

The Functions Of The Myelin Sheath

Write a short note on myelin sheath and the process of myelination of a peripheral nerve fiber.
Answer.

The thick axons of peripheral nerves are surrounded by myelin sheath, which is made up of concentric layers of plasma membrane of Schwann cells and lipids (fatty substance) between these layers. It is formed by Schwann cells by a process called myelination.

Formation of myelin sheath (myelination)

The Schwann cells are first arranged in a linear fashion (end to end) along the nerve fiber and surround it.

• The axon invaginates the side of the Schwann cell. As a result, the plasma membrane of the Schwann cell forms a mesaxon, which suspends the axon within the Schwann cell.
• The Schwann cell now rotates around the axon again and again, i.e. repeatedly. Consequently, the axon becomes spirally wrapped by many layers of elongated mesaxon. Later, the inner layers of the plasma membrane fuse with each other so that the axon becomes surrounded by several layers of modified membrane.
• The lipids are deposited between adjacent layers of the membrane. These layers of mesaxon along with lipids constitute the myelin sheath. The nerve fibers surrounded by myelin sheath are termed myelinated fibers.

Functions of myelin sheath

Provides support to nerve fibers.

• Aids speed in the conduction of nerve impulses.
• Insulates the axons from the extracellular environment.
• Provides white color to nerve fibers.
• Helps in the regeneration of nerve fibers.