Corpus: Nerve

A nerve is an anatomical structure that serves to conduct excitation. A nerve consists of many bundled nerve fibers and the connective tissue surrounding them.

Nerves are usually named systematically according to their leading structure (e.g. ulnar nerve) or their supply area (e.g. medial dorsal cutaneous nerve, facial nerve), but sometimes also according to anatomical features (e.g. vagus nerve). They branch out along their course through the body and give off fiber bundles to neighboring structures, which are also addressed either as a distinct nerve (nervus) or as a branch (ramus). Branches that create fiber connections between two neighboring nerves are referred to as rami communicantes or nerve anastomoses.

In the area of the origin of the extremities, nerves also exchange fibers to a greater extent and thus form nerve plexuses.

Nerves can be further differentiated histologically. The connective tissue involved in the structure of the nerve is divided into 3 zones:

3.1. Endoneurium

The endoneurium is the loose connective tissue that surrounds the Schwann cells of the individual nerve fibers. It contains numerous small blood and lymph vessels that nourish the Schwann cells and thus also the nerve fibers they encase. Occasionally, free cells (e.g. macrophages) are also found.

3.2. Perineurium

The perineurium is a tight connective tissue that combines many individual nerve fibers into common bundles, the so-called fascicles. It supports and subdivides ("septates") the nerve – comparable to the plastic core of a multi-stranded cable. The connective tissue cells are in close, epithelial-like contact with each other and are connected by so-called tight junctions.

3.3. Epineurium

The epineurium surrounds the nerve together with the larger vessels that supply it to the outside. It is a connective tissue with numerous collagen fibers, to which an additional "shifting layer" of loose connective tissue or fatty tissue, the so-called mesoneurium, can be attached.

4.1. ...according to function

A distinction is made according to the function of the fiber qualities running in them:

• Motor nerves
• Sensory or sensitive nerves
• Mixed nerves

4.2. ...according to topography

A distinction is made according to their origin:

• Cranial nerves: nerves that originate directly from the brain
• Spinal nerves: nerves that originate from the spinal cord
• Peripheral nerves: nerves that supply the organs of success outside the brain and spinal cord and thus represent the final route of the sensorimotor and autonomic nervous system.

The inflammation of a nerve is called neuritis. A distinction is made depending on the number of nerves affected:

• Mononeuritis
• Polyneuritis