Nerve innervation is a term used to describe the distribution of nerves across the body and to particular areas, along with the supply of nerve impulses. Doctors study nerve innervation extensively in medical school, often with the assistance of dissection in an anatomy laboratory, and they are responsible for knowing how every nerve in the body is distributed. Understanding nerve innervation is key to the diagnosis and treatment of many medical conditions, ranging from diagnosing neurological problems to learning to avoid critical nerves during general surgery.
The nervous system starts with the brain, which descends to the spinal cord. Nerves branch off in all directions and they lead to many different parts of the body. The optic nerve, for example, innervates the eye, and it is a classical example of dense nerve innervation, meaning that many nerves are clustered into a very small area. Nerves can be voluntary or involuntary, depending on where they originate and what they do. Voluntary nerves can be controlled by a person's conscious thoughts, while involuntary nerves are part of the body's autonomic processes which keep the body functioning.
The hands are another area of dense nerve innervation, reflecting the highly specialized functions of the hands and the need for precise control. Nerves enter the hand at the wrist and distribute across the palm to the fingers, allowing people to control their hands to perform an assortment of tasks, from grasping a fork to performing neurosurgery. Dense innervation also allows very precise and detailed sensory information to return to the brain.
Sometimes, nerve innervation can lead along some surprising pathways. For example, the vagus nerve innervates many of the visceral organs, despite the fact that branches of nerves along the spinal cord are much closer to the viscera than the vagus nerve. The vagus nerve provides involuntary innervation, keeping the abdominal organs at work on a variety of tasks even when a person is asleep.
Knowing which nerve innovates what part of the body can be important for neurologists, as they can use information about the body to narrow down areas of damage along the nervous system. For example, doctors can find the precise area of damage in the spinal cord in cases of paralysis by determining which areas of the body are paralyzed. Brain damage can also cause problems with nerve innervation, as in the case of people who experience damage to their brainstems which makes them unable to breathe independently.