What is a Lower Motor Neuron?

A lower motor neuron refers to a nerve that communicates with the muscles to bring about movement. An important part of the nervous system, these neurons begin in the spinal cord and branch out throughout the body. Signals are then carried through these nerves so the body can function properly.

The nervous system is divided into two parts, the central and peripheral systems. Consisting of the brain and spinal cord, the central nervous system, also known as the CNS, organizes and directs all the information gathered from the nerves. The peripheral nervous system, or PNS, contains the rest of the nerves that run through the body. The PNS is then divided into the autonomic and somatic systems.

The autonomic nervous system is in charge of bodily functions that are involuntary such as breathing, digesting and regulating the heart rate. The somatic nervous system manages voluntary actions or movements a person performs consciously. Muscle contractions are an example of a voluntary action. The somatic system is where the lower motor neuron operates.

The connection that a lower motor neuron makes is part of the efferent nerve arrangement. Efferent neurons or nerves, also called motor or effector nerves, are responsible for transporting the messages from the central nervous system to the rest of the body. These signals are then put together to produce a conscious action such as muscle contraction to allow the body to move purposefully.

When there is damage to lower motor neuron the transmission of messages may become hampered. Called a lower motor neuron lesion, a condition resulting in nerve impairment from an injury or disease process can produce a decrease or loss of muscle control or body movements. This reduction in signal communication and muscle control typically presents flaccid paralysis.

Flaccid paralysis from a lower motor neuron lesion is characterized by a decline in muscle tone. Muscle tone, a necessary component in maintaining posture, is the bodily process where the muscles sustain a certain level of tightness. When there is a decline in muscle tone, general muscle weakness can also occur. In extreme cases, paralysis or an inability to move may be present.

This general reduction in muscle function seen in a lower motor neuron lesion may also result in a condition called muscle wasting if the impairment is longstanding. Muscle wasting is a situation where the muscles shrink or begin to lose their size. If the lesion does not heal, denervation or the destruction of the nerve can occur, producing a permanent loss of function.