Corticonuclear Tracts

Front 1

Lower Motor Neurons of the cranial nerves

Back 1

function like alpha motor neurons of the spinal cord.
They are not as large (their axons don’t have to be quite as long) but they are still multipolar neurons controlled by upper motor neurons (called ‘corticobulbar fibers’).
Note, visual system is kept together, so VI and V are out of numeric order.

Front 2

Oculomotor nucleus

Back 2

in midbrain (superior colliculus), inferiormost aspect of periaquiductal gray matter, adjacent to MLF. Nerve passes through the red nucleus then continues to exit the midbrain anteriorly. Oculomotor nucleus controls all but two eye muscles. Edinger-Westphal nucleus, on the superior aspect of the oculomotor nucleus, is parasympathetic to the ciliary body and sphincter pupillae muscles.

Front 3

Trochlear nucleus

Back 3

: in midbrain (~inferior colliculus), in inferior periaquiductal gray, adjacent to MLF. Axons exit from tectum of mesencephalon. Supplies the superior oblique M. of the eye.

Front 4

Abducent nucleus

Back 4

In the lower pons. The axons of the Facial nerve arch around (and occasionally through) this nucleus. Exits the pons anteriorly to supply the lateral rectus M. of the eye.

Front 5

Trigeminal motor system

Back 5

1. Nucleus is in the tegmentum of the upper pons, just medial to the chief sensory nucleus of the trigeminal nerve (already discussed). The complete Trigeminal nerve exits the pons laterally.
2. Lesion to nucleus or nerve results in paralysis of ipsilateral muscles of mastication. Usually, proximity of motor and sensory areas will also result in loss of touch sensation to face.

Front 6

Facial motor system.

Back 6

1. Found in the tegmentum of the lower pons. The motor nerve axons proceed dorsally around the Abducent nucleus then course ventrally to exit anteriolaterally. They are joined from parasympathetic preganglionic axons from the superior salivatory nucleus, which supplies the submandibular ganglion via the chorda tympani.
2. Damage to nucleus or nerve results in complete ipsilateral paralysis of muscles of facial expression

Front 7

Glossopharyngeal and Vagus nuclei

Back 7

1. There are two different functions involved; skeletal motor and parasympathetic. Both components are associated with Glossopharyngeal and Vagus nerve. The glossopharyngeal nerve passes out from the area of the pontomedullary junction anteriolaterally, whereas the vagal nerve roots exit the open medulla just superior to the inferior olivary nucleus.
2. Skeletal motor component: Nucleus Ambiguus. This is a poorly identified region of the open medulla, found in the medullary tegmentum between inferior cerebellar peduncle and the inferior olivary nucleus. The uppermost part will be associated with the glossopharyngeal nerve, the lower part the Vagus nerve. The lowermost part is associated with the "cranial" portion of the accessory nerve; however, in humans, it seems this rarely is associated with the XI nerve, but instead joins the Vagus nerve. The nucleus ambiguus supplies motor control of the muscles of the pharynx (more superiorly) and larynx (more inferiorly). Note, there are regional tendencies in control, but no absolute demarcation between the two.
3. Parasympathetics. The inferior salivatory nucleus joins the motor and sensory fibers of the Glossopharyngeal nerve to exit with it as a whole. The inferior salivatory nucleus regulates secretion of the Parotid gland. The Dorsal Motor Nucleus of the Vagus nerve, in the lower open medulla into the upper closed medulla, is responsible for all vagal preganglionic parasympathetic axons, from the neck region all the way to the midgut (hindgut and pelvis being supplied by sacral parasympathetics).