A nerve cell (i.e., spinal motoneuron) innervating a muscle. Thus, it is an efferent neuron that originates in the spinal cord and synapses with muscle fibers to facilitate muscle contraction and with muscle spindles to modify proprioceptive sensitivity. Motoneurons in both the somatic and autonomic nervous system (ANS) originate in the ventral gray column of the spinal cord. Autonomic fibers innervate cardiac muscle of the heart and smooth muscle of the visceral organs and glands, while somatic fibers innervate skeletal muscle. In the ANS, the pathway of a motoneuron consists of two motoneurons that synapse on an autonomic ganglion. Consequently, motoneurons of the ANS are called pre-ganglionic and post-ganglionic depending on their position relative to their ganglion. In contrast, the comparable pathway in the somatic nervous system is composed of a single motoneuron. Another classification of motoneurons depends on the neurotransmitter they release adrenergic in the case of those releasing norepinephrine, and cholinergic if they release acetylcholine. In fact, all motoneurons are cholinergic except for most postganglionic fibers of the sympathetic nervous system, which are adrenergic. Sympathetic postganglionic fibers, however, that innervate sweat glands and certain blood vessels are cholinergic.
See Acetylcholine, Alpha (α) motoneuron, Autonomic nervous system (ANS), Axon, Axon retraction (or pruning), Cholinergic neurotransmitter system, Corticobulbar tract (CBT), Corticospinal tract (CST), Extrafusal muscle fibers, Extrapyramidal system, Eye movements, Final common pathway, Gamma (γ) motoneuron, Ganglia, Golgi tendon organ, Interneurons, Motor cortex, Motor end plate, Motor unit, Muscle fiber, Muscle spindle, Neurogenesis, Neuron, Noredrenergic neurotransmitter system, Somatic nervous system (SNS), Synapse