Motorneuronne

Motorneuronne, also referred to as motor neuron or neurone moteur, denotes a nerve cell that transmits signals from the central nervous system to skeletal muscles, triggering contraction and movement. In humans, motor neurons are located in the brainstem motor nuclei and in the ventral horns of the spinal cord; their axons extend into peripheral nerves to reach muscle fibers. They form the final common pathway for motor control, receiving inputs from upper motor neurons and interneurons that regulate initiation, precision, and force of movement.

There are two main classes: alpha motor neurons, which innervate extrafusal muscle fibers responsible for generating force, and gamma motor neurons, which innervate intrafusal fibers of muscle spindles to adjust stretch-sensing sensitivity. Many cranial nerves that control head and neck muscles also contain motor neurons in their nuclei.

The motor neuron communicates with muscle fibers at the neuromuscular junction. An action potential arriving at the presynaptic terminal opens voltage-gated calcium channels, triggering the release of acetylcholine, which activates nicotinic receptors on the motor end plate. This produces an endplate potential that leads to muscle contraction through excitation-contraction coupling.

Clinical relevance includes degeneration or dysfunction of motor neurons, as seen in amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy, which cause progressive weakness, muscle atrophy, and fasciculations. Diagnosis often involves electromyography and imaging of motor pathways.

Developmentally, motor neurons arise from the ventral spinal cord and brainstem motor nuclei and rely on trophic support from CNS targets and peripheral muscles for maintenance and function.