Hermopäällyksen

Hermopäällyksen, also known as myelin sheath, is a fatty insulating layer that surrounds the axons of many neurons. This protective covering is crucial for the efficient transmission of electrical signals, known as nerve impulses, throughout the nervous system. The myelin sheath is produced by specialized glial cells: oligodendrocytes in the central nervous system (brain and spinal cord) and Schwann cells in the peripheral nervous system (nerves outside the brain and spinal cord).

The structure of the myelin sheath is segmented, with gaps called nodes of Ranvier occurring at regular intervals along the axon. This segmented arrangement allows for a process called saltatory conduction, where the nerve impulse "jumps" from one node of Ranvier to the next. This jumping mechanism significantly increases the speed at which nerve impulses travel compared to unmyelinated axons, which conduct signals continuously along their length.

Myelination, the process of forming the myelin sheath, begins during fetal development and continues into adolescence. The presence and integrity of the myelin sheath are essential for normal neurological function. Diseases that damage or destroy the myelin sheath, such as multiple sclerosis, can lead to severe neurological impairments, including problems with movement, sensation, and cognition. The composition of myelin is primarily lipids and proteins, with specialized proteins like myelin basic protein playing key roles in its structure and function.