motoraxons

Motoraxons are the axons of motor neurons that conduct impulses from the central nervous system to skeletal muscles, forming the efferent component of the neuromuscular system. They originate in motor neurons located in the ventral horn of the spinal cord and in motor nuclei of the brainstem. From there, they exit the CNS via ventral roots or cranial nerves and travel through peripheral nerves to their muscle targets.

Most motoraxons are myelinated and capable of rapid conduction; conduction velocity increases with axon diameter and myelination. They form motor units by branching to multiple muscle fibers within a given muscle, allowing coordinated force production. Alpha motor axons innervate extrafusal muscle fibers responsible for generating muscle tension, while gamma motor axons innervate intrafusal fibers of muscle spindles to modulate proprioceptive sensitivity.

At the neuromuscular junction, motoraxon terminals release acetylcholine, which binds to nicotinic receptors on the motor endplate and initiates muscle contraction. Transmission can be altered by toxins, pharmacological agents, or neuropathic disease affecting the axon, the terminal, or the postsynaptic endplate.

Clinical relevance includes disorders that damage motoraxons or their pathways. Degeneration or injury can cause weakness, atrophy, and fasciculations. Neurodegenerative diseases such as amyotrophic lateral sclerosis affect both upper and lower motor neurons and their axons; other conditions include spinal muscular atrophy, peripheral neuropathies, demyelinating diseases, and neuromuscular junction disorders. Injury can also lead to Wallerian degeneration distal to the site of axonal damage.