What is a "fiber"?

In the nervous system, fiber refers to the long, thin extensions of neurons that transmit electrical impulses to other neurons or to muscles and glands. These fibers, also called axons, are covered in a protective sheath called myelin, which helps to speed up the transmission of impulses. The myelin sheath is produced by specialized cells called oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. Damage to the myelin sheath, such as in the case of multiple sclerosis, can cause disruptions in nerve impulse transmission and lead to a range of neurological symptoms, including muscle weakness, numbness, and vision problems.