Cranial Nerve Nuclei In

Medulla Oblongata

By

Hassan Mohammad Al-ShehriID#2051040006

Cranial nerve nuclei in Medulla Oblongata

Introduction:

The 'medulla oblongata' is the lower portion of the brainstem. By anatomical terms of location, it is rostral to the spinal cord and caudal to the pons, which is in turn ventral to the cerebellum.

Controls autonomic functions and relays nerve signals between the brain and spinal cord.

The medulla is often thought of as being in two parts, an open part (close to the pons), and a closed part (further down towards the spinal cord). The 'opening' referred to is on the dorsal side of the medulla, and forms part of the fourth ventricle of the brain.

Running down the ventral aspect of the medulla are the pyramids which contain corticospinal fibers. On the open medulla, there is a slight bulge just behind the pyramids called the olive or olivary nuclei.

In Medulla Oblongata we have many nuclei: Vestibulocochlear Nucleus (VIII) - Which found in pons and medulla Hypoglossal nucleus (XII) - motor Dorsal motor nucleus of vagus nerve (X) - visceromotor Nucleus ambiguous (IX, X, XI) - motor Solitary nucleus (VII, IX, X) - sensory Spinal trigeminal nucleus (V) - sensory Inferior olivary nucleus afferent fibers to cerebellum

Vestibulocochlear Nucleus

Vestibular nerve:

The 'Vestibulocochlear nerve' is the eighth of twelve cranial nerves and also known as the auditory nerve or acoustic nerve. It is the nerve along which the sensory cells (the hair cells) of the inner ear transmit information to the brain. It consists of the cochlear nerve, carrying information about hearing, and the vestibular nerve, carrying information about balance. It emerges from the medulla oblongata and enters the internal acoustic meatus in the temporal bone, along with the facial nerve.

Axons of the vestibular nerve synapse in the vestibular nucleus on the lateral floor and wall of the fourth ventricle in the pons and medulla. The vestibular nerve goes to the semicircular canals via the vestibular ganglion. It receives positional information.

The eighth nerve runs through the internal auditory meatus together with the facial nerve. The primary afferent vestibular neurons project to four nuclei that comprise the vestibular nuclear complex in the floor of the medulla beneath the fourth ventricle.

The four nuclei of the vestibular nuclear complex are the lateral vestibular nucleus (also called Deiter's nucleus), the medial vestibular nucleus, the superior vestibular nucleus, and the inferior vestibular nucleus.

The vestibular nuclei receive afferent fibers from the utricle and saccule and the semicircular canals through the vestibular nerve and fibers from the cerebellum through the inferior cerebellar peduncle. The efferent fibers come from the nuclei and it will pass to the cerebellum through the inferior cerebellar peduncle. Efferent fibers also descend uncrossed fibers to the spinal cord from the lateral vestibular nucleus and from the vestibulospinal tract. In addition, efferent fibers pass to the nuclei of the occulomotor, trochler, and abducent nerves through the medial longitudinal fasciculus.

Cochlear nuclei:

The cochlear nuclei consist of:

(a) the dorsal cochlear nucleus, corresponding to the tuberculum acusticum on the dorso-lateral surface of the inferior peduncle; and

(b) The ventral or accessory cochlear nucleus, placed between the two divisions of the nerve, on the ventral aspect of the inferior peduncle.

The cell groups related to the other division of C.N. VIII, the vestibular nuclei, lie medial to the inferior cerebellar peduncle.

They receive afferent fibers from the cochlea through the cochlear nerve.The primary input to both cochlear nuclei is from the auditory portion of C.N. VIII. The axons making up this division of C.N. VIII consist of the central processes of neurons that lie in the spiral or cochlear ganglion.

Glossopharyngeal Nerve Nuclei

The IX nerve has no real nucleus to itself. Instead it shares nuclei with VII and X and these nuclei are main motor, parasympathetic and sensory nucleus.

Main motor nucleus:It lies deep in the reticular formation of the medulla oblongata and is formed by the superior end of the nucleus ambiguus. It receives corticonuclear fibers from both cerebral hemispheres. The efferent fibers supply the stylopharyngeus muscle.

Parasympathetic nucleus:This nucleus is also called the inferior salivary nucleus. It lies in the medulla just medial to the nucleus ambiguus.It receives afferent from hypothalamus, olfactory system, and from nucleus of solitary tract. Preganglionic parasympathetic axons arising from cells in the inferior salivatory nucleus end within the OTIC GANGLION. Postganglionic axons then pass to the parotid gland where they stimulate secretion.

Sensory nucleus:It’s a part of the nucleus of the TRACTUS SOLITARIUS.Sensation of taste travel through the peripheral axon of the nerve cells situated in the ganglion on glossopharyngeal nerve. Afferent impulse from the carotid baroreceptors are sent via the glossopharyngeal nerve. They terminate in the nucleus of tractus solitarius.

Vagus nerve nuclei

The vagus nerve (also called pneumogastric nerve or cranial nerve X), and it’s the only nerve that starts in the brainstem (within the medulla oblongata).

The vagus nerve has three associated nuclei, the dorsal motor nucleus, the nucleus ambiguus and the solitary nucleus.

Nucleus ambiguus:It’s a motor nucleus. It lies deep in the reticular formation of the medulla oblongata. It receives corticonuclear fibers from both cerebral hemispheres. It innervates striated muscle throughout the neck and thorax. This includes some muscles of the palate and pharynx, muscles of the larynx, and the parasympathetic innervations of the heart.

Dorsal nucleus of the vagus:This nucleus arises from the floor of the fourth ventricle. It nucleus lies slightly dorsal and lateral to the hypoglossal nucleus. It receives afferent from hypothalamus and from glossopharyngeal. the efferent fibers is going to the involuntary muscle of bronchi , heart , esophagus , stomach , small intestine , and the large intestine until one third of the transverse colon. This is secretomotor parasympathetic nucleus. Secretomotor primarily means that it stimulates glands - including mucus glands of the pharynx, lungs, and gut, as well as gastric glands in the stomach.

Solitary nucleus:It receives taste information, sensation from the back of the throat, and also visceral sensation. Visceral sensation includes blood pressure receptors, blood-oxygen receptors, sensation in the larynx and trachea, and stretch receptors in the gut. Most information goes from the solitary nucleus to the thalamus and hypothalamic nuclei. Afferent information concerning general sensation enters the brain stem through the superior ganglion of the vagus nerve but end the spinal nucleus of the trigeminal nerve.

Accessory nerve

Traditional descriptions distinguish two parts to the accessory nerve:

A spinal part, formed from axons of spinal nucleus. It receives corticospinal fibers from both cerebral hemispheres. That innervates the muscles around the neck -- specifically, the sternocleidomastoid muscle (sternomastoid) and trapezius muscle on the ipsilateral side.

A cranial part, formed from the axons of nucleus ambiguus. The afferents from corticonuclear fibers from both cerebral hemispheres. The efferents emerge from the anterior surface of the medulla oblongata between the olive and inferior peduncle.

Hypoglossal nucleus

This nucleus lies just off the midline beneath the floor of the fourth ventricle. It receives corticonuclear fibers from both cerebral hemispheres. Axons from cells within the hypoglossal nucleus course ventrally to exit the medulla between the pyramid and the inferior olive. The hypoglossal nerve then passes through the hypoglossal foramen to emerge from the base of the skull. Each nerve innervates the ipsilateral intrinsic and extrinsic muscles of the tongue.

Examination of lesion in cranial nerves

Vestibule cochlear nerve :

Vestibular: Lesions involving the vestibular nerve, nuclei, and descending pathways will result in problems such as stumbling or falling toward the side of the lesion. Vestibular function can be investigated with caloric tests. These involve the rising and lowering of the temperature in the external auditory meatus which induce convection currents in the endolymph of the semicircular canals (principally the lateral semicircular canal) and stimulates the vestibular nerve endings.

Cochlear: Lesions involving the cochlear nerve will manifest in deafness and tinnitus. Its function can be investigated by a tuning fork.

Glossopharyngeal nerve :The gag reflex is absent in patients with damage to the glossopharyngeal nerve as it is responsible for the afferent limb of the reflex.

Vagus nerve:Check for hoarseness, and asking the patient to say "AH"

Accessory nerve :Getting a person to raise and lower their shoulders while you push down tests trapezius. When a person turns their head, especially against force, sternocleidomastoid should be prominent.

HypoglossalProblem with the hypoglossal nerve can be detected by asking the patient to stick out his tongue. The tongue will deviate towards the weak side, towards the side of the lesion.

Nerve Function How to test

VIII hearing a tuning fork

balance look for vertigo

IX pharynx sensation gag reflex

Xmuscles of larynx

and pharynx, parasymp.

check for hoarseness, open

wide and say "AH"

XItrapezius and

sternocleidomastoid

test shoulder raise or turning

the head

XII tongue muscles stick out the tongue