| Cranial Nerve V: Trigeminal Entrance To Brainstem: Exit From Brainstem: Location Of Associated Nuclei In Brainstem: Major Functions Largest of cranial nerves; fibers extend from pons to face, and form three divisions: opthalmic, maxillary, and mandibular divisions. Major general sensory nerves of face; transmit afferent impulses from touch, temperature, and pain receptors; cell bodies of sensory neurons of all three divisions are located in large trigeminal ganglion; the mandibular division also contains some motor fibers that innervate chewing muscles. Opthalmic Division (V1) Fibers run from face to pons via superior orbital fissure. Function: Conveys sensory impulses from skin of anterior scalp, upper eyelid, and nose, and from nasal cavity mucosa, cornea, and lacrimal gland. Maxillary Division (V2) Fibers run from face to pons via foramen rotundium. Function: Conveys sensory impulses from nasal cavity mucosa, palate, upper teeth, skin of cheek, upper lip, lower eyelid. Mandibular Division (V3) Fibers pass through skull via foramen ovale. Function: Conveys sensory impulses from the anterior tongue (except taste buds), lower teeth, skin of chin, temporal region of scalp; supplies motor fibers to, and carries proprioceptor fibers from, muscles of mastication. (MARIEB) Anatomy: Contains large sensory root, which carries sensation from the skin and mucosa of most of the head, and asmall motor root, which innervates most of the chewing muscles (masseter, temporalis, pterygoids, mylohyoid), and the tensor tympani muscle of the middle ear. Efferent fibers (the minor portion) originate in the motor nucleus of V in the pons; this cell group receives input from the corticobulbar tracts and reflex connections from the spinal tract of nerve V and controls the muscles involved in chewing. The sensory root (the main portion of the nerve) arises from cells in the semilunar ganglion in a pocket of dura (Meckel’s cavity) lateral to the cavernous sinus. It passes posteriorly between the superior petrosal sinus in the tentorium and the skull base and enters the pons. The ophthalmic division fibers enter the cranial cavity through the superior orbital fissure. The maxillary division fibers pass through the foramen rotundum. The mandibular division sensory fibers, joined by the motor fibers involved in mastication, course through the foramen ovale. Trigeminal nerve fibers carrying light touch project to the main (principle) trigeminal nucleus. After synapsing, this pathway passes from the nerve’s main sensory nucleus via crossed fibers in the ventral trigeminothalmic-thalmic tract and via uncrossed fibers in the dorsal trigeminothalmic tract, to the ventral posteromedial nuclei of the thalamus and higher centers. Pain and temperature fibers in the trigeminal nerve enter the brain stem, turn caudally, and descend for a short distance within the spinal tract of V. These fibers then synapse with secondary neurons in the spinal nucleus of V. From there, the pathway passes to the thalmus via the ventral trigeminothalmic tract. Proprioceptive fibers in the trigeminal nerve project to the mesencephalic trigeminal nucleus (mesencephalic nucleus of V), where their cell bodies are located. Collaterals project to the motor nucleus of V. The reflex connections pass to the cerebellum and the motor nuclei of cranial nerves V, VII, and IX. (WAXMEN) |
| Cranial Nerve VII: Facial Entrance To Brainstem: Exit From Brainstem: Location Of Associated Nuclei In Brainstem: Major Functions Fibers issue from the pons, just lateral to abducens nerves, enter temporal bone via the internal acoustic meatus, and run within bone (and through inner ear cavity) before emerging through stylomastoid foramen; nerve then courses to the lateral aspect of the face. Function: Mixed nerves that are the chief motor nerves of face; have five major branches: temporal, zygomatic, buccal, mandibular and cervical. Convey motor impulses to skeletal muscles of face (muscles of facial expression), except for chewing muscles served by trigeminal nerves, and transmit proprioceptor impulses from same muscles to pons Transmit parasympathetic (autonomic) motor impulses to lacrimal (tear) glands, nasal, and palatine glands, and submandibular and sublingual salivary glands. Some of the cell bodies of these parasympathetic motor neurons are in sphenopalatine and submandibular ganglia on the trigeminal nerve Convey sensory impulses from taste buds of anterior two-thirds of tongue; cell bodies of these sensory neurons are in geniculate ganglion (MARIEB) The facial nerve consists of the facial nerve proper and the nervus intermedius. Both parts pass through the internal auditory meatus, where the geniculate ganglion for the taste component lies. The facial nerve proper contains axons that arise in the facial (VII) nucleus. The nerve exits through the stylomastoid foramen; it innervates the muscles of facial expression, the platysma muscle, and the stapedius muscle of the inner ear. The nervus intermedius sends parasympathetic preganglionic fibers to the pterygopalatine ganglion to innervate the lacrimal gland and, via the chorda tympani nerve to the submaxillary and sublingual ganglia in the mouth, to innervate the salivary glands. The visceral afferent component of the nervus intermedius, with cell bodies in the geniculate ganglion, carries taste sensation from the anterior two thirds of the tongue, via the chorda tympani to the solitary tract and nucleus. The somatic afferent fibers from the skin of the external ear are carried in the facial nerve to the brainstem. These fibers connect there to the trigeminal nuclei and are, in fact, part of the trigeminal sensory system. The superior salivatory nucleus receives cortical impulses from the nucleus of the solitary tract via the dorsal longitudinal fasciculus and reflex connections. Visceral efferent axons run from the superior salivatory nucleus via nerve VII to the pterygopalatine and submandibular ganglia. They synapse there with postganglionic parasympathetic neurons that innervate the submandibular and sublingual salivary glands. The taste fibers run through the chorda tympani and the nervus intermedius to the solitary nucleus, which is connected with the cerebral cortex through the medial lemnisci and the VPM nucleus of the thalamus and with the salivatory nucleus and motor nucleus of VII by reflex neurons. The cortical taste area is located in the inferior central (face) region; it extends onto the opercular surface of the parietal lobe and adjacent insular surface. (WAXMAN) |
| Cranial Nerve VIII: Vestibulocochlear Entrance To Brainstem: Exit From Brainstem: Location Of Associated Nuclei In Brainstem: Major Functions Fibers arise from hearing and equilibrium apparatus located within inner ear of temporal bone and pass through internal acoustic meatus to enter brain stem at pons-medulla border; afferent fibers from hearing receptor in cochlea form the cochlear division; those from equilibrium receptors in semicircular canals and vestibule form the vestibular division (vestibular nerve); the two divisions merge to form vestibulocochlear nerve. Function: Purely sensory; vestibular branch transmits afferent impulses for sense of equilibrium; and sensory nerve cell bodies are located in vestibular ganglia; cochlear branch transmits afferent impulses for sense of hearing, and sensory nerve cell bodies are located in spiral ganglion within cochlea. (MARIEB) Cranial nerve VIII is a double nerve that arises from spiral and vestibular ganglia in the labyrinth of the inner ear. It passes into the cranial cavity via the internal acoustic meatus and enters the brain stem behind the posterior edge of the middle cerebellar peduncle in the pontocerebellar angle. The cochlear nerve is concerned with hearing (audition); the vestibular nerve is part of the system of equilibrium (position sense). (WAXMAN) |
| Cranial Nerve IX: Glossopharyngeal Entrance To Brainstem: Exit From Brainstem: Location Of Associated Nuclei In Brainstem: Major Functions Fibers emerge from medulla and leave skull via jugular foramen to run to throat. Function: Mixed nerves that innervate part of the tongue and pharynx; provide motor fibers to, and carry proprioceptor fibers from, superior pharyngeal muscles involved in swallowing and gag reflex; provide parasympathetic motor fibers to parotid salivary gland (some of the nerve cell bodies of these parasympathetic motor neurons are located in otic ganglion). Sensory fibers conduct taste and general sensory (touch, pressure, pain) impulses from pharynx and posterior tongue, from chemoreceptors in the carotid body (which monitor O2 and CO2 tension in the blood and help regulate respiratory rate and depth), and from pressure receptors of carotid sinus (which help to regulate blood pressure by providing feddback information); sensory neuron cell bodies are located in superior and inferior ganglia. (MARIEB) Cranial nerve IX contains several types of fibers. Branchial efferent fibers from the ambiguous nucleus pass to the stylopharyngeal muscle. Visceral efferent (parasympathetic preganglionic) fibers from the inferior salivatory nucleus pass through the tympanic plexus and lesser petrosal nerve to the otic ganglion, from which the postganglionic fibers pass to the parotid gland. The inferior salivatory nucleus receives cortical impulses via the dorsal longitudinal fasciculus and reflexes from the nucleus of the solitary tract. Visceral afferent fibers arise from unipolar cells in the inferior (formerly petrosal) ganglia. Centrally, they terminate in the solitary tract and its nucleus, which in turn projects to the thalmus (VPM nucleus) and then to the cortex. Peripherally, the visceral affeent axons of nerve IX supply general sensation to the pharynx, soft palate, posterior third of the tongue, fauces, tonsils, auditory tube, and tympanic cavity. Through the sinus nerve, they supply special receptors in the carotid body and carotid sinus that are concerned with reflex control of respiration, blood pressure, and heart rate. Special visceral afferents supply the taste buds of the posterior third of the tongue and carry impulses via the superior ganglia to the gustatory nucleus of the brainstem. A few somatic affeent fibers enter by way of the glossopharyngeal nerve and end in the trigeminal nuclei. The tongue receives its sensory innervation through multiple pathways: Three cranial nerves contain taste fibers (nerve VII for anterior one third of tongue; Nerve IX for posterior one third of tongue; nerve X for epiglottis), and the general sensory afferent fibers are mediated by nerve V. (WAXMAN) |
| Cranial Nerve X: Vagus Entrance To Brainstem: Exit From Brainstem: Location Of Associated Nuclei In Brainstem: Major Functions The only cranial nerves to extend beyond head and neck region; fibers emerge from medulla, pass through skull via jugular foramen, and descend through the neck region into the thorax and abdomen. Function: Mixed nerves; nearly all motor fibers are parasympathetic efferents, except those serving skeletal muscles of the pharynx and larynx (involved in swallowing); parasympathetic motor fibers supply heart, lungs, and abdominal viscera and are involved in regulationof heart rate, breathing, and digestive system activity; transmit sensory impulses from thoracic and abdominal viscera, from the carotid sinus (pressoreceptor for blood pressure) and taste buds of posterior tongue and pharynx; carry proprioceptor fibers from muscles of larynx and pharynx. (MARIEB) Branchial efferent fibers from the ambiguous nucleus contribute rootlets to the vagus nerve and the cranial component of the accessory nerve (XI). Those of the vagus nerve pass to the muscles of the soft palate and pharynx. Those of the accessory nerve join the vagus outside the skull and pass, via the recurrent laryngeal nerve, to the instrinsic muscles of the larynx. Visceral efferent fibers from the dorsal motor nucleus of the vagus course to the thoracic and abdominal viscera. Their postganglionic fibers arise in the terminal ganglia within or near the viscera. They inhibit heart rate and adrenal secretion and stimulate gastrointestinal peristalsis and gastric, hepatic, and pancreatic glandular activity. Somatic afferent fibers of unipolar cells in the superior (formerly called the jugular) ganglion send peripheral branches via the auricular branch of nerve X to the external auditory meatus and part of the earlobe. They also send peripheral branches via the recurrent meningeal branch to the dura of the posterior fossa. Cnetral branches pass with nerve X to the brainstem and end in the spinal tract of the trigeminal nerve and its nucleus. Visceral afferent fibers of unipolar cells in the inferior (formerly nodose) ganglion send peripheral branches to the pharynx, larynx, trachea, esophagus, and the thoracic and abdominal viscera. They also send a few special afferent fibers to taste buds in the epiglottic region. Central branches run to the solitary tract and terminate in its nucleus. The visceral afferent fibers of the vagus nerve carry the sensations of abdominal distention and nausea and the impulses concerned with regulating the depth of respiration and controlling blood pressure. A few special visceral afferent fibers for taste from the epiglottis pass via the inferior ganglion to the gustatory nucleus of the brainstem. The ambiguous nucleus receives cortical connections from the corticobulbar tract and reflex connections from the extrapyramidal and tectobulbar tracts and the nucleus of the solitary tract. (WAXMAN) |
| Cranial Nerve XI: Accessory Entrance To Brainstem: Exit From Brainstem: Location Of Associated Nuclei In Brainstem: Major Functions Unique in that they are formed by union of a cranial root and a spinal root; crania root emerges from the lateral aspect of medulla of brainstem; spinal root arises from superior region (C1 – C5) of spinal cord. Spinal portion passes upward along spinal cord, enters skull via foramen magnum, and temporarily joins cranial root; the resulting accessory nerve exits from the skull through juglular foramen; then cranial and spinal fibers diverge; cranial root fibers join vagus nerve, while spinal root runs to the largest neck muscles. Function: Mixed nerves, but primarily motor in function; cranial division joins with fibers of vagus nerve (X) to supply motor fibers to larynx, pharynx, and soft palate; spinal root supplies motor fibers to trapezius and sternocleidomastoid muscles, which together move head and neck and conveys proprioceptor impulses from same muscles. MARIEB The accessory nerve consists of two separate components: the cranial component and the spinal component. In the cranial component, branchial efferent fibers (from the ambiguous nucleus to the instrinsic muscles of the larynx) join the accessory nerve inside the skull but are part of the vagus outside the skull. In the spinal component, the branchial efferent fibers from the lateral part of the anterior horns of the first five or six cervical cord segments ascend as the spinal root of the accessory nerve through the foramen magnum and leave the cranial cavity through the jugular foramen. These fibers supply the sternocleidomastoid muscle and partly supply the trapezius muscle. The central connections of the spinal component are those of the typical lower motor neuron: voluntary impulses via the basal ganglia, and reflexes via the vestibulospinal and tectospinal tracts. (WAXMAN) |
| Cranial Nerve XII : Hypoglossal Entrance To Brainstem: fibers arise by a series of roots from medulla Exit From Brainstem: from skull via hypoglossal canal to travel to tongue. Location Of Associated Nuclei In Brainstem: Major Functions: Mixed nerves, but primarily motor in function; carry somatic motor fibers to intrinsic and extrinsic muscles of tongue, and proprioceptor fibers from same muscles to brainstem; hypoglossal nerve control allows not only food mixing and manipulation by tongue during chewing, but also tongue movements that contribute to swallowing and speech. Somatic efferent fibers from the hypoglossal nucleus in the ventromedian portion of the gray matter of the medulla emerge between the pyramid and the olive to form the hypoglossal nerve. The nerve leaves the skull through the hypoglossal canal and passes to the muscles of the tongue. A few proprioceptive fibers from the tongue course in the hypoglossal nerve and end in the trigeminal nuclei of the brainstem. The hypoglossal nerve distributes motor branches to the geniohyoid and infrahyoid muscles with fibers derived from communicating branches of the first cervical nerve. A sensory recurrent meningeal branch of nerve XII innervates the dura of the posterior fossa of the skull. Central connections of the hypoglossal nucleus include the corticobulbar (corticonuclear) motor system (with crossed fibers), as well as reflex neurons from the sensory nuclei of the trigeminal nerve and the nucleus of the solitary tract. (WAXMAN) |
Last Updated 09/06/01 08:53:32 PM
Return To The MNA2001 Homepage