Upper motor neurons in the brain send motor information to the medulla or spinal cord, while lower motor neurons carry this information to muscles. Different pathways control different movements, with the pyramidal tract controlling conscious movement and extrapyramidal tracts controlling subconscious processes. Both upper and lower motor neurons must function properly for proper muscle movement.
An upper motor neuron is a neuron, or nerve cell, that exists in the brain and sends higher-level motor information to the medulla, located in the brain, or to the proper spinal cord level outside the brain. From the cord or spinal cord, lower motor neurons carry motor information to muscle fibers, making them much more directly responsible for movement than upper motor neurons. An upper motor neuron can be found in a couple of different parts of the brain. Upper motor neurons are usually concentrated in the motor region of the brainstem or cerebral cortex; they send motor information down from there.
There are many different pathways along which an upper motor neuron can send electrical impulses that ultimately result in motion. The rubrospinal tract, for example, is heavily involved in involuntary movements to improve and maintain body balance. Most of the movements related to this stretch occur in the arms. The tectospinal tract is related to the movements of the neck muscles and the reticulospinal tract plays an important role in controlling autonomic actions in the body. The corticospinal tract, or pyramidal tract, largely controls conscious movement and muscle action.
In general, an upper motor neuron in the pyramidal tract will have a role in conscious movement control while an upper motor neuron in an extrapyramidal tract, or any pathway outside the pyramidal tract, will likely be involved in a subconscious motor process such as balance or posture . The pyramidal tract begins in the cerebral cortex, specifically in the section of the frontal lobe known as the motor strip. In general, nerve impulses travel from this motor strip to the spinal cord.
The lower motor neurons receive information from the upper motor neurons and transmit it to the real muscle fibers in both conscious and autonomous movements. Therefore, both the upper and lower neuronal tracts must function properly to facilitate the proper transfer of nerve impulses from the brain to the muscles. A disturbance in either side can cause motor problems of varying severity.
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