Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 137 of 367 The Trochlear Nerves (IV) A trochlear nerve (IV), the smallest cranial nerve, innervates the superior oblique muscle of each eye. The trochlea is a pulley-shaped, ligamentous sling. Each superior oblique muscle passes through a trochlea on its way to its insertion on the surface of the eye. An individual with damage to cranial nerve IV or to its nucleus will have difficulty looking down and to the side. The Trigeminal Nerves (V) The pons contains the nuclei associated with three cranial nerves (V, VI, and VII) and contributes to a fourth (VIII). The trigeminal nerves (V), the largest cranial nerves, are mixed nerves. Each provides both somatic sensory information from the head and face and motor control over the muscles of mastication. The Abducens Nerves (VI) The abducens nerves (VI) innervate the lateral rectus muscles, the sixth pair of extra-ocular muscles. Contraction of the lateral rectus muscle makes the eye look to the side; in essence, the abducens causes abduction of the eye. The Facial Nerves (VII) The facial nerves (VII) are mixed nerves. On each side, the sensory and motor roots emerge from the pons and enter the internal acoustic meatus of the temporal bone. Each facial nerve then passes through the facial canal to reach the face by way of the stylomastoid foramen. The nerve then splits to form the temporal, zygomatic, buccal, mandibular, and cervical branches. The sensory neurons monitor proprioceptors in the facial muscles, provide deep pressure sensations over the face, and receive taste information from receptors along the anterior two-thirds of the tongue. Somatic motor fibers control the superficial muscles of the scalp and face and deep muscles near the ear. The Vestibulocochlear Nerves (VIII) The vestibulocochlear nerves (VIII) are also known as the acoustic nerves, the auditory nerves, and the stato-acoustic nerves. Each vestibulocochlear nerve lies posterior to the origin of the facial nerve, straddling the boundary between the pons and the medulla oblongata. This nerve reaches the sensory receptors of the inner ear by entering the internal acoustic meatus in company with the facial nerve. These nerves convey information about the orientation and movement of the head. The Glossopharyngeal Nerves (IX) The medulla oblongata contains the sensory and motor nuclei of cranial nerves IX, X, XI, and XII, in addition to the vestibular nucleus of nerve VIII. The glossopharyngeal nerves (IX) innervate the tongue and pharynx. Each glossopharyngeal nerve penetrates the cranium within the jugular foramen, with nerves X and XI. The Vagus Nerves (X) The vagus nerves (X) arise immediately posterior to the attachment of the glossopharyngeal nerves. Each vagus nerve provides somatic sensory information about the external acoustic meatus (a portion of the external ear) and the diaphragm, and special sensory information from pharyngeal taste receptors. But most of the vagal afferents carry visceral sensory information from receptors