An exception is the trochlear nucleus in the brainstem, which innervates the superior oblique muscle of the eye on the opposite side of the face.

For example, the oculomotor nucleus contains α-MNs that innervate muscles of the eye, and is found in the midbrain, the most rostral brainstem component.

By contrast, the hypoglossal nucleus, which contains α-MNs that innervate the tongue, is found in the medulla, the most caudal (i.e., towards the bottom) of the brainstem structures.

Alpha motor neurons originate in the basal plate, the ventral portion of the neural tube in the developing embryo.

Those α-MNs that do not receive sufficient neurotrophic factors will undergo apoptosis, a form of programmed cell death.

Because they innervate many muscles, some clusters of α-MNs receive high concentrations of neurotrophic factors and survive this stage of neuronal pruning.

Upper motor neurons (UMNs) send input to α-MNs via several pathways, including (but not limited to) the corticonuclear, corticospinal, and rubrospinal tracts.

The corticonuclear and corticospinal tracts are commonly encountered in studies of upper and lower motor neuron connectivity in the control of voluntary movements.

Similarly, UMNs of the cerebral cortex are in direct control of α-MNs of the spinal cord via the lateral and ventral corticospinal tracts.

There are several types of reflex circuits, the simplest of which consists of a single synapse between a sensory neuron and a α-MNs.

Like other neurons, α-MNs transmit signals as action potentials, rapid changes in electrical activity that propagate from the cell body to the end of the axon.

To increase the speed at which action potentials travel, α-MN axons have large diameters and are heavily myelinated by both oligodendrocytes and Schwann cells.

One way they differ is that synapses between neurons typically use glutamate or GABA as their neurotransmitters, while the neuromuscular junction uses acetylcholine exclusively.

Alpha motor neurons have Aα axons, which are large-caliber, heavily myelinated fibers that conduct action potentials rapidly.

By contrast, gamma motor neurons have Aγ axons, which are slender, lightly myelinated fibers that conduct less rapidly.

For example, poliomyelitis is caused by a virus that specifically targets and kills motor neurons in the ventral horn of the spinal cord.

For example, myasthenia gravis is an autoimmune disease that prevents signaling across the neuromuscular junction, which results in functional denervation of muscle.