Cranial Neves IX, X & XI Dr. Nimir Dr. Safaa

Glossopharyngeal Nerve (Cranial Nerve IX) It is a motor and a sensory nerve. Glossopharyngeal nerve nuclei are three nuclei: (1) Main motor nucleus(SVE). (2) Parasympathetic nucleus(GVE). (3) Sensory nucleus(GVA). Main Motor Nucleus: It lies deep in reticular formation of medulla oblongata and is formed by superior end of nucleus ambiguus. It receives corticonuclear fibers from both cerebral hemispheres. Efferent fibers supply stylopharyngeus muscle.

Parasympathetic Nucleus: It is also called inferior salivatory nucleus. It receives: Afferent fibers from hypothalamus through descending autonomic pathways. Information from olfactory system through reticular formation. Information concerning taste from nucleus of solitary tract from mouth cavity. Efferent preganglionic parasympathetic fibers reach otic ganglion through tympanic branch of glossopharyngeal, tympanic plexus, and lesser petrosal nerve. Postganglionic fibers pass to parotid salivary gland.

Sensory Nucleus: It is part of nucleus of tractus solitarius. Sensations of taste travel through peripheral axons of nerve cells situated in ganglion on glossopharyngeal nerve. Central processes of these cells synapse on nerve cells in sensory nucleus. Efferent fibers cross and ascend to ventral nuclei of thalamus and hypothalamic nuclei. From thalamus through internal capsule and corona radiata fibers end in lower part of the postcentral gyrus.

Afferent concerns common sensation enters brainstem through superior ganglion of glossopharyngeal but ends in spinal nucleus of trigeminal. Afferent impulses from carotid sinus baroreceptor travel with glossopharyngeal & terminate in nucleus of tractus solitarius and connected to dorsal motor nucleus of vagus nerve. Carotid sinus reflex that involves glossopharyngeal and vagus nerves assists in regulation of arterial blood pressure.

Course of Glossopharyngeal Nerve: It leaves anterolateral surface of upper medulla oblongata between olive and inferior cerebellar peduncle. It passes laterally in posterior cranial fossa and leaves skull through jugular foramen. Superior and inferior glossopharyngeal sensory ganglia are situated on nerve here. The nerve descends through upper part of the neck with internal jugular vein and internal carotid artery to reach posterior border of stylopharyngeus muscle, which it supplies. The nerve then passes forward between superior and middle constrictor muscles of pharynx to give sensory branches to mucous membrane of pharynx and posterior third of tongue.

Vagus Nerve (Cranial Nerve X) It is a motor and a sensory nerve. Vagus Nerve Nuclei: It has three nuclei: (1) Main motor nucleus. (2) Parasympathetic nucleus. (3) Sensory nucleus. Main Motor Nucleus: It lies deep in reticular formation of medulla oblongata and is formed by nucleus ambiguus. It receives corticonuclear fibers from both cerebral hemispheres. The efferent fibers supply constrictor muscles of pharynx intrinsic muscles of the larynx.

Parasympathetic Nucleus: It forms dorsal nucleus of vagus and lies beneath floor of lower part of fourth ventricle posterolateral to hypoglossal nucleus. It receives: Afferent fibers from hypothalamus through descending autonomic pathways. Afferents from glossopharyngeal (carotid sinus reflex). Efferent fibers are distributed to involuntary muscle of bronchi, heart, esophagus, stomach, small intestine, and large intestine as far as distal one-third of transverse colon.

Sensory Nucleus: It is lower part of nucleus of tractus solitarius. Sensations of taste travel through peripheral axons of nerve cells situated in inferior ganglion on vagus nerve. Central processes of those cells synapse on nerve cells in sensory nucleus. Efferent fibers cross the median plane and ascend to ventral nuclei of thalamus & hypothalamic nuclei. From thalamus through internal capsule and corona radiata fibers end in postcentral gyrus. Afferent concerns common sensation enters brainstem through superior ganglion of vagus but ends in spinal nucleus of trigeminal.

Course of the Vagus Nerve It leaves anterolateral surface of upper medulla oblongata between olive and inferior cerebellar peduncle. It passes laterally through posterior cranial fossa and leaves skull through jugular foramen. The vagus nerve has two sensory ganglia: Rounded superior on the nerve within jugular foramen. Cylindrical inferior which lies on the nerve just below the foramen. At inferior ganglion, cranial root of accessory nerve joins vagus and is distributed mainly in its pharyngeal and recurrent laryngeal branches.

Vagus descends in neck within carotid sheath with internal jugular vein and internal and common carotid arteries. Right vagus enters thorax and passes posterior to root of right lung, contributing to pulmonary plexus. It then passes on to posterior surface of esophagus and contributes to the esophageal plexus. It enters abdomen through esophageal opening of diaphragm as posterior vagal trunk which is distributed to posterior surface of stomach, duodenum, liver, kidneys, small and large intestines as far as distal third of transverse colon. This wide distribution is accomplished through the celiac, superior mesenteric, and renal plexuses.

Left vagus enters thorax and crosses left side of aortic arch and descends behind root of left lung, contributing to pulmonary plexus. Then descends on anterior surface of esophagus, contributing to esophageal plexus. It enters abdomen through esophageal opening of diaphragm as anterior vagal trunk and divides into several branches, which are distributed to stomach, liver, upper part of duodenum, and head of pancreas.

Accessory Nerve (Cranial Nerve XI) It is a motor nerve that is formed by the union of a cranial and a spinal root. Cranial Root: It is formed from axons of nerve cells of the nucleus ambiguus which receives corticonuclear fibers from both cerebral hemispheres. Efferent fibers of nucleus emerge from anterior surface of medulla oblongata between olive and inferior cerebellar peduncle.

Course of the Cranial Root: The nerve runs laterally in posterior cranial fossa and joins spinal root. The two roots unite and leave skull through the jugular foramen then separate and cranial root joins vagus and is distributed in its pharyngeal and recurrent laryngeal branches to muscles of soft palate, pharynx, and larynx.

Spinal Root: It is formed from axons of nerve cells in spinal nucleus which is situated in the anterior gray column of spinal cord in upper five cervical segments. Spinal nucleus is thought to receive corticospinal fibers from both cerebral hemispheres.

Course of the Spinal Root: Nerve fibers emerge from spinal cord midway between the anterior and posterior roots of cervical spinal nerves. The fibers form a nerve trunk that ascends into skull through foramen magnum. Spinal root passes laterally and joins cranial root as they pass through jugular foramen. After a short distance, spinal root separates and runs downward and laterally and enters the deep surface of sternocleidomastoid muscle, which it supplies . The nerve then crosses posterior triangle of neck and passes beneath trapezius muscle, which it supplies. The accessory nerve thus brings about movements of soft palate, pharynx, larynx and controls movement of two large muscles in the neck.