Nerven

Nerven are bundles of nerve fibers in the peripheral nervous system that transmit electrical impulses between the brain and spinal cord and the rest of the body. Each nerve contains axons from many neurons, surrounded by connective tissue layers: an inner endoneurium around individual fibers, a middle perineurium around fascicles, and an outer epineurium that encases the whole nerve. Nerves may also contain blood vessels. They can be classified by the type of information they carry: sensory (afferent), motor (efferent), or mixed.

Nerves connect the central nervous system to muscles, glands, and sensory receptors. Cranial nerves originate from the brain, while spinal nerves arise from the spinal cord and often form networks called plexuses in the neck, arm, and leg regions. Autonomic fibers, part of the peripheral nervous system, innervate smooth muscle, cardiac muscle, and glands and include sympathetic and parasympathetic pathways.

Conduction along a nerve fiber is an action potential that travels more rapidly along myelinated axons through saltatory conduction. Myelin in the peripheral nervous system is produced by Schwann cells; the nodes of Ranvier facilitate faster transmission by concentrating the electrical impulses at these gaps.

Injury to a nerve can cause loss of sensation or motor function in the area served by the nerve. In the peripheral nervous system, axons can regenerate to a degree, guided by Schwann cells and the endoneurial tubes, whereas central nervous system repair is limited. Nerve disorders include neuropathies and entrapment syndromes such as carpal tunnel, which may require clinical assessment and, in some cases, surgical repair or nerve grafting.