Motornaceller

Motornaceller are nerve cells that control skeletal muscle contraction, enabling voluntary movements. They form the final common pathway for motor commands, receiving inputs from the brain and spinal interneurons and transmitting signals to muscles.

Their cell bodies reside in the ventral horn of the spinal cord (lower motor neurons) and in brainstem motor nuclei for cranial nerves; their axons extend through peripheral nerves to reach skeletal muscles. They link the central nervous system with the periphery and are essential for initiating and regulating muscle activity.

Two main types are alpha motor neurons, which innervate extrafusal muscle fibers to generate force, and gamma motor neurons, which innervate intrafusal muscle fibers in muscle spindles to regulate stretch sensitivity. At the neuromuscular junction, motor neurons release acetylcholine onto nicotinic receptors on the muscle, triggering contraction. A motor unit comprises a single motor neuron and all the muscle fibers it controls.

Motor commands descend from the cortex and brainstem via the corticospinal and extrapyramidal pathways to the spinal cord and brainstem motor neurons, integrating with spinal reflex circuits. Proper function depends on intact connectivity between the central nervous system and muscles; disruptions can lead to impaired movement.

Clinical relevance: degeneration or injury of motornaceller causes weakness, muscle wasting, fasciculations, and altered reflexes. Diseases include amyotrophic lateral sclerosis, spinal muscular atrophy, and poliomyelitis. Diagnosis often uses electromyography and nerve conduction studies; treatment is typically supportive and focuses on maintaining mobility and function.

Development and regeneration: motor neurons arise from neural progenitors in the developing neural tube and differentiate under signaling cues to establish connections with muscle targets. Peripheral nerves can regenerate after injury, but central motor pathways have limited regenerative capacity.