Which cranial nerves exit at the pontomedullary junction

Which cranial nerves exit at the pontomedullary junction? 

  • Cranial nerve 6 exits medially, and cranial nerves 7 and 8 exit laterally

The Abducens nerve (cranial nerve VI) – Is a motor nerve that emerges anteriorly and medially from the junction of the pons and medulla.  

The abducens nucleus is in the midline of the inferior tegmentum of the pons just ventral to the fourth ventricular floor.

It provides innervation to the lateral rectus muscle, which is responsible for the abduction of the eye.

The facial nerve (cranial nerve VII) – Emerges from the junction of the pons and the medulla lateral to the abducens nerve at the cerebellopontine angle. It is both a motor and a sensory nerve and emerges as two separate roots; these include a medial motor root and a lateral sensory root.

The facial motor nucleus situates in the anterior lateral inferior pons, just anterior and medial to the spinal trigeminal nucleus. The muscles of facial expression derive innervation from the motor nucleus of the facial nerve.

The upper face receives corticobulbar fibers that partially decussate from both hemispheres, which allows sparing of deficits with lesions at the level of the cranial nerve nuclei while the lower muscles corticobulbar fibers fully decussate. The sensory nucleus is the upper portion of the solitary nucleus, which is located posterior and lateral to the facial nerve motor nucleus.

It receives afferent fibers for taste from the anterior two-thirds of the tongue and sensation for the skin near the auricle of the ear.

Its parasympathetic nucleus is the superior salivatory nucleus and is located laterally to the abducens nucleus but posterior to the facial motor nucleus. It innervates the submandibular and submental salivary glands.

The Vestibulocochlear nerve (cranial nerve VIII) – Arises from the brainstem directly lateral to the sensory root of the facial nerve. Cranial nerve VIII has two distinct portions, the vestibular, responsible for balance, and the cochlear, which is responsible for hearing.

Cranial nerve VIII is purely a sensory nerve, and both of its portions course together until they reach their nuclei within the brainstem.  The vestibular portion of the nerve provides input to the vestibular nuclei located along the lateral portion of the fourth ventricle in the inferior pons.

The vestibular nuclei are composed of four different nuclei (superior, inferior, lateral, and medial.) These nuclei send tracts to three separate areas: the cerebellum via the vestibulocerebellar tract, the spinal cord through the vestibulospinal tract, and the nuclei of cranial nerves III, IV, and VI by the medial longitudinal fasciculus.

The cochlear portion provides input to the dorsal and ventral cochlear nuclei. These nuclei are in the anterior lateral portion of the inferior pons. The posterior cochlear nucleus processes high-frequency sounds, while the anterior cochlear nucleus processes low-frequency sound.

The anterior cochlear nucleus projects fibers to the ipsilateral superior olive and then to the lateral lemniscus. The posterior cochlear nucleus projects to the contralateral lateral lemniscus.

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