Motor portion: Originates in the pons and terminates on hair cells of the spiral organ;
Function: Vestibular branch sensory function: Conveys impulses related to equilibrium. Vestibular branch motor function: Adjust sensitivity of hair cells. Cochlear branch sensory function: Conveys impulses for hearing. Cochlear branch motor function: Modifies function of hair cells by altering their response to sound waves;
Clinical application: Injury to the vestibular branch may cause vertigo (a subjective feeling of rotation), ataxia (muscular incoordination and nystagmus (involuntary rapid movement of the eyeball). Injury to the cochlear branch may cause tinnitus (ringing in the ears) or deafness;
IX. Glossopharyngeal nerve (mixed)
Nuclei: a) nucleus tractus solitarius b) inferior salivary nucleus c) nucleus ambiguous. In medulla oblongata dorsally, in region of trigonum of vagal nerve as continuation of nucleus of this nerve b)cells of nucleus scattered in reticular formation of medulla oblongata between nucleus ambiguus and nucleus of olive c)reticular formation of medulla oblongata);
Site where nerve leaves the brain or enters in: Lower than two previous ones, in superior posterolateral sulcus passing dorsally of olive;
Site of exit from the cranium: Jugular foramen;
Sensory portion: Consists of axons from taste buds and somatic sensory receptors on posterior one-third of the tongue, from proprioceptors in swallowing muscles supplied by the motor portion, and from stretch receptors in carotid sinus and chemoreceptors in carotid body near the carotid arteries. Axons pass through the jugular foramen and end in the medulla;
Motor portion: Originates in the medulla and passes through the jugular foramen. Axons of somatic motor neurons innervate the stylopharyngeus muscle, a muscle of pharynx that elevates the larynx during swallowing. Parasympathetic axons innervate the parotid (salivary) gland;
Function: Sensory function: Taste and somatic sensation (touch, pain, temperature) from posterior third of tongue; proprioception in swallowing muscles; monitoring of blood pressure; monitoring of O2 and CO2 in blood for regulation of breathing rate and depth. Somatic motor function: Elevates the pharynx during swallowing and speech. Autonomic motor function (parasympathetic): Stimulates secretion of saliva;
Clinical application: Injury causes difficulty in swallowing, reduced secretion of saliva, loss of sensation in the throat, and loss of taste sensation.
X. Vagus nerve (mixed)
Nuclei: a) nucleus of tractus solitarii b) dorsal nucleus of vagus nerve c) nucleus ambiguous. a) Region of vagal triangle in medulla oblongata; b) same region dorsally of previous one; c) reticular formation of medulla oblongata, deeper than dorsal nucleus of vagus nerve;
Site where nerve leaves the brain or enters in: From same sulcus as glossopharyngeal nerve but more caudally of it;
Site of exit from the cranium: jugular foramen;
Sensory portion: Consists of axons from small number of taste buds in the epiglottis and pharynx, proprioceptors in muscles of the neck and throat, stretch receptors and chemoreceptors in carotid sinus and carotid body near the carotid arteries, chemoreceptors in aortic body near arch of the aorta, and visceral sensory receptors in most organs of the thoracic and abdominal cavities. Axons pass through the jugular foramen and end in the medulla and pons;
Motor portion: Originates in medulla and passes through the jugular foramen. Axons of somatic motor neurons innervate skeletal muscles in the throat and neck. Parasympathetic axons innervate smooth muscle in the airways, esophagus, stomach, small intestine, most of large intestine, and gallbladder; cardiac muscle in the heart; and glands of the gastrointestinal (GI) tract;
Sensory function: Taste and somatic sensations (touch, pain, temperature, and proprioception) from epiglottis and pharynx; monitoring of blood pressure; monitoring of O2 and CO2 in blood for regulation of breathing rate and depth; sensations from visceral organs in thorax and abdomen. Somatic motor function: Swallowing, coughing, and voice production;
Autonomic motor function (parasympathetic): Smooth muscle contraction and relaxation in organs of the gastrointestinal tract; slowing of the heart rate; secretion of digestive fluids;
Clinical application: Injury interrupts sensations from many organs in the thoracic and abdominal cavities, interferes with swallowing, paralyzes vocal cords, and causes heart rate to increase.
XI. Accessory nerve (mixed, mainly motor)
Nuclei: a) Nucleus ambiguous b) spinal nucleus of accessory nerve medulla oblongata as continuation of the nucleus of the same name in the IX and X pairs b) spinal cord, between anterior and posterior horns of grey matter);
Site where nerve leaves the brain or enters in: Cranial roots from the same sulcus as vagus nerve, but more caudally spinal roots between anterior and posterior roots of cervical nerves, at level of segments C2 - C5 ;
Site of exit from the cranium: Jugular foramen;
Sensory portion: Consists of axons from proprioceptors in muscles of the pharynx, larynx, and soft palate that pass through the jugular foramen and end in the medulla;
Motor portion: Consists of a cranial root and a spinal root. Cranial root arises in the medulla, passes through the jugular foramen, and supplies muscles of the pharynx, larynx, and soft palate. Spinal root originates in the anterior gray horn of the first five cervical segments of the spinal cord, passes through the jugular foramen, and supplies the sternocleidomastoid and trapezius muscles. Sensory function: Proprioception. Somatic motor function: Cranial part mediates swallowing movements; spinal part mediates movement of head and shoulders;
Clinical application: If nerves are damaged, the sternocleidomastoid and trapezius muscles become paralyzed, with resulting inability to raise the shoulders and difficulty in turning the head. Irritation of in field of innervation may cause torticollis.
XII. Hypoglossal (mixed, mainly motor)
Nuclei: Nucleus of hypoglossal nerve (locates in medulla oblongata in hypoglossal triangle);
Site where nerve leaves the brain or enters in: Anterolateral sulcus of medulla oblongata between pyramid and olive;
Site of exit from the cranium: Anterior condylar canal;
Sensory portion: Consists of axons from proprioceptors in tongue muscles that pass through the hypoglossal canal and end in the medulla;
Motor portion: Originates in the medulla, passes through the hypoglossal canal, and supplies muscles of the tongue;
Sensory function: Proprioception;
Motor function: Movement of tongue during speech and swallowing;
Clinical application: Injury results in difficulty in chewing, speaking, and curls toward the affected side, and the affected side atrophies.
Glossoplegia - paralysis of the tongue. Hemiglossoplegia - paralysis of the half of tongue.