hermosäie

Hermosäie is the Estonian term for a nerve fiber, the elongated projection of a neuron that conducts electrical impulses along a nerve. In common usage the term describes the axon and its myelin sheath, though some definitions emphasize the axon itself and its surrounding glial coverings. A single nerve fiber transmits signals within the nervous system, linking neurons to other neurons, muscles, or glands.

Structure and variants: A nerve fiber is typically an axon surrounded by a myelin sheath in the peripheral nervous system, produced by Schwann cells, or by oligodendrocytes in the central nervous system. Myelination speeds conduction via saltatory conduction between nodes of Ranvier. Some fibers remain unmyelinated or have thinner myelin, resulting in slower signal transmission. Fibers are commonly categorized by diameter and conduction velocity into A, B, and C classes, with A fibers being the fastest and C fibers the slowest.

Function: Nerve fibers carry sensory information from the body to the central nervous system and convey motor commands from the CNS to muscles. They also transmit autonomic signals to glands and smooth muscles. The functional output depends on fiber type, myelination status, and the neural pathway involved.

Clinical relevance: Damage or disease affecting nerve fibers can disrupt signal transmission, causing sensory loss, weakness, pain, or autonomic dysfunction. Examples include demyelinating conditions such as multiple sclerosis (central) and Guillain-Barré syndrome (peripheral), as well as various inherited or acquired neuropathies. Diagnosis often involves nerve conduction studies and imaging.

Context and connective tissue: Nerve fibers form part of nerves that are organized with connective tissue layers—endoneurium around individual fibers, perineurium around fascicles, and epineurium around the whole nerve. They develop from neurons and depend on glial support for maintenance.