Innervation

Innervation is the distribution of nerve fibers to a body region, enabling motor control, sensation, and autonomic regulation. The nervous supply travels through the peripheral nervous system and is arranged into somatic and autonomic components.

Somatic innervation provides voluntary motor control via motor neurons that project to skeletal muscles, and conveys conscious and proprioceptive sensation through sensory neurons in skin, muscles, and joints. Autonomic innervation regulates involuntary functions and includes the sympathetic and parasympathetic divisions, as well as the enteric system within the gut. Sympathetic activity generally prepares the body for arousal and energy expenditure, while parasympathetic activity promotes rest and digestion. Many organs receive dual innervation from both divisions, often with opposing effects, though some tissues rely predominantly on one division.

Peripheral nerves contain mixed fiber types, including motor efferents, sensory afferents, and autonomic fibers. In the autonomic system, nerve fibers often synapse in autonomic ganglia before reaching their targets. Sensory innervation conveys information such as touch, pain, temperature, and proprioception, while motor innervation transmits commands to muscles. The enteric nervous system can function independently to regulate gut motility and secretion, though it interacts with central autonomic pathways.

Damage to innervation—due to trauma, disease, or compression—can result in loss of sensation, weakness, paralysis, or autonomic dysfunction. Understanding innervation patterns is fundamental to anatomy, physiology, and clinical medicine.