Innervation: Function, Tasks, Role & Diseases

Innervation connects organs, tissues, and body parts to the nervous system, enabling complex interactions within the body. Electrical and biochemical stimuli are transmitted through the nerve cells and nerve fibers. Damage to nerve structures can result in motor dysfunction, insensations, and even life-threatening consequences.

What is innervation?

In medicine, innervation is the functional supply network of nerve tissue. Organs as well as body parts or tissue types such as muscle tissue are innervated with nerve cells and nerve fibers. In medicine, innervation is the functional supply network of nerve tissue. Organs as well as body parts or tissue types such as muscle tissue are innervated with nerve cells and nerve fibers. Nerve cells (neurons) are responsible for the perception of stimuli and the processing of nerve impulses. Nerve fibers are the extensions of the nerve cells. They are also called axons including the adjacent sheath structures and conduct electrical excitation away from the nerve cell body. Innervation by axons, their sheaths and neurons ultimately ensures the functioning of all bodily processes. Somatic innervation is what neurologists refer to as sensory and motor innervation. Vegetative innervation is vital and is divided into sympathetic and parasympathetic innervation.

Function and task

Innervation performs sensitive, autonomic, and motor functions in the body. Sensory nerve fibers are connected to receptors. These receptors register sensations. An example is the mechanoreceptors of the skin layers, which register touch and pressure. The nociceptors perceive pain stimuli and the thermoreceptors of the skin are responsible for temperature perception. The nerve fibers connected to these sensory receptors transmit the excitations afferently, i.e. toward the central nervous system. This transmission usually occurs via projection and ensures that a stimulus reaches the brain and ultimately the thinking consciousness. Within the group of sensory innervation, we sometimes speak of sensory innervation when referring to the sensory organs of the eye, ear, and pharynx. Innervation of the internal organs, on the other hand, is also called viscerosensory innervation. These nerve fibers transmit sensations from the internal organs to the central nervous system. In most cases, however, these neurons and axons are counted as part of the autonomic nervous system, since life would not be possible without this conduction of excitation. The autonomic nervous system consists of parasympathetic, sympathetic and enteric innervation. These nerve connections control digestion, respiration, glandular functions and the movement of the heart muscle. Unlike the heart muscle, skeletal muscles are not connected to an autonomic nervous system. They are innervated by motor nerves. That is, excitation is transmitted to their individual muscle fibers via what is called the motor end plate. In this way, a command from the central nervous system stimulates the skeletal muscles to contract. In this case, stimuli are therefore not transmitted into the central nervous system, but out of the central nervous system. In connection with the motor nerves of the skeletal muscles, physicians therefore also speak of efferent innervation. However, afferent nerve fibers also run into each muscle, registering the current tone of the muscles and transmitting them to the central nervous system. The transmission of action potentials within the nervous system is either biochemical or bioelectrical. In biochemical transmission, so-called neurotransmitters are used. These neurotransmitters are biochemical messengers. They are secreted by one nerve cell and recognized by other nerve cells. In this way, even nerve cells that are not directly next to each other can communicate. Electrical transmission in the nervous system, on the other hand, takes place with the help of charged salt particles from the cell membranes. The membrane potential of the cells results from the difference between the external and internal environment of the cell. This difference is detected by the membrane and is present as an electrical voltage. In this way, a compensating current is generated, which forms the core of electrical signal transmission. Overall, the perception, movement and internal processes of an organism would not be possible without innervation.

Diseases and ailments

In the nervous system, nerve cells can die due to various processes. One of the most common causes is lack of blood flow. For example, due to a stoppage of the heart, blood flow is interrupted, possibly allowing nerve tissue to be damaged. Often, in this case, the innervation of the brain is affected. This cell death of nerve cells in the brain can cause different symptoms. Motor functions can be affected as well as perception. Metabolic disorders of the nerve tissue can also trigger dysfunctions or impaired stimulus transmission. In such metabolic disorders, toxins often accumulate in the brain. Inflammations in the nervous system can cause just as much damage. Such phenomena occur, for example, in multiple sclerosis, in which the immune system mistakenly recognizes the body’s own cells as foreign and attacks tissues of the central nervous system. The most common early symptoms of nervous system damage are taste confusion, movement disorders, or sensory disturbances such as numbness and tingling. Mal sensations can be present, for example, in the form of diabetic polyneuropathy, in which lack of blood flow is responsible for the damage. Infectious diseases such as Lyme disease or degenerative diseases can also be associated with damage to the nervous system. In some circumstances, even mechanical injuries such as traumatic brain injury can affect the nervous system. In severe cases, nerves are severed in an accident. This can also result in numbness or motor impairment. In addition, nerve damage in the spine is particularly dangerous. It can happen that severed nerves grow out, forming a neuroma that causes considerable pain. Today, severed nerves may be able to be rejoined. However, this process is extremely lengthy, since nerve fibers grow only one millimeter per day. Therapeutic success therefore only occurs after a significantly longer time than is the case, for example, with the healing of bone fractures or wounds.