COLLEGE OF DENTAL SCIENCES DEPARTMENT OF PERIODONTICS
CRANIAL NERVERS IXth, XIth AND XIIth
DR. CHETAN CHANDRA
• ATTACHMENT OF THE CRANIAL NERVES TO THE BRAINSTEM.
• GLOSOPHARYNGEAL NERVE (IXTH CRANIAL NERVE)
• SPINAL ACCESSORY NERVE (XITH CRANIAL NERVE)
• HYPOGLOSSAL NERVE (XIITH CRANIAL NERVE)
All cranial nerves are attached to the surface of the brain. The olfactory and optic nerves are attached to the cerebral hemispheres. The remaining nerves are attached to the brainstem. The occulomotor nerve is attached to the midbrain on the anteromedial aspect of the cerebral peduncle. The trochlear nerve emerges from the posterior surface of the brainstem, just below the inferior colliculus. The trigeminal nerve is attached to the front of the pons where the latter becomes continuous with the middle cerebellar peduncle. The abducent nerve emerges at the lower border of the pons, immediately to the pyramid. The facial nerve (and nervus intermedius) also emerges at the lower border of the pons, cranial to the olive. The vestibulocochlear nerve is attached to the lower border of the pons just later to the facial nerve. The rootlets of the glossopharyngeal, vagus and accessory nerves emerge through the posterolateral sulcus of the medulla (in line with dorsal nerve roots of spinal nerves). The rootlets of the hypoglossal nerve emerge through the anterolateral sulcus of the medulla (in line with ventral nerve roots of spinal nerves).
INTRODUCTION FUNCTIONAL COMPONENTS COURSE AND RELATIONS BRANCHES AND DISTRIBUTION OTIC GANGLION CLINICAL CONSIDERATIONS CLINICAL TESTING OF GLOSSOPHARYNGEAL NERVE I) INTRODUCTION: The glossopharyngeal or ninth cranial nerve (from glosso, “tongue”, and pharynx, “throat”) is a mixed branchiomeric nerve. It is the nerve of the third (III rd) branchial arch. It is attached to the lateral side of the upper part of the medulla (between the olive and the inferior cerebellar peduncle) by three or four roots. Glossopharyngeal Nerve
1) Motor to 2) Secretomotor to 3) Gustatory to 4) Sensory to: Stylopharyngeus
Pharynx, tonsils & Post.1/3rdof tongue.
It runs forwards and laterally and leaves the cranial cavity by passing through the middle part of the jugular foramen. At the base of the skull IX
nerve forms two sensory ganglia i.e superior and
inferior petrosal ganglia. Superior petrosal ganglion is small and gives no branches. 4
Inferior petrosal ganglion is larger & occupies a notch on the lower border of the petrous temporal bone. II) FUNCTIONAL COMPONENTS :-
A) General visceral efferent fibers: Preganglionic fibers arise in the inferior salivary nucleus and travel to the otic ganglion. Postganglionic fibers arising in the otic ganglion supply the parotid gland.
B) Special visceral efferent fibers: Arises in nucleus ambiguus. Supplies stylopharyngeous muscle.
C) General visceral afferent: Fibers are peripheral processes of cell in the inferior ganglion of the nerve. They carry general sensations (touch, pain, temperature) from the pharynx and the posterior part of the tongue to the ganglion. The central processes convey these sensations to the nucleus of the solitary tract.
D) Special visceral afferent: Fibers are also peripheral process of the cell in the inferior ganglion. They carry sensations of taste from the posterior one third of the tongue to the ganglion. The central processes convey these sensations to the nucleus of solitary tract.
III) COURSE AND RELATIONS:Intracranial course Fibers of nerve pass forwards and laterally between the Olivary nucleus and the inferior cerebellar peduncle through the reticular formation of the medulla.
At the base of brain Nerve is attached by 3 to 4 filaments to the upper part of the posterolateral sulcus of the medulla, just above the rootlets of the vagus nerve.
Leaves the skull Filaments unite to form a single trunk and leave the skull by passing through the middle part of the jugular foramen anterior to the X th and XI th cranial nerves. It has a separate sheath of duramater.
Extracranial course Emerging at the base of the skull the nerve passes forwards and laterally between the internal jugular vein (which is posterolateral to it) and Internal carotid Artery (which is anterolateral to it). It then passes deep to styloid process and muscles attached to it. Winds around stylopharyngeus & passes between external and internal carotid arteries and reaches the side of pharynx. It enters the submandibular region by passing deep to the hypoglossus, where it breaks up into tonsillar and lingual branches.
BRANCHES AND DISTRIBUTION:-
Tympanic Carotid Pharyngeal Muscular Tonsillar Lingual 1) Tympanic nerve (Jacobson’s nerve) : The tympanic nerve arises from the inferior sensory ganglion. It passes through a canal (called the inferior tympanic canaliculus) within the petrous part of the temporal bone and reaches the tympanic cavity and forms a plexus (Tympanic plexus). Branches arising from this plexus supply the : Mucous membrane of the tympanic cavity. The auditory tube The mastoid air cells. The tympanic nerve then perforates the roof of the cavity and having lost its sensory fibers, is known as the lesser petrosal nerve. It leaves the cranial cavity by passing through the foramen ovale. The nerve ends by joining the otic ganglion. 2) Carotid branch : The carotid branch arises soon after the glosso-pharyngeal nerve emerges on the base of the skull. It supplies the baroreceptors of carotid sinus and chemoreceptors of the carotid body. These two tiny organs are blood pressure regulatory mechanisms that are located close to the bifurcation of the common carotid artery. 3) Pharyngeal branches: Take pharyngeal nerve fibers join with vagus (Xth) and the spinal accessory (XIth) nerves to form the pharyngeal plexus. 7
This network supplies the muscles of the pharynx and soft palate, except for the tensor veli palatine and the stylopharyngeus muscles. Also this plexus provides sensory fibers to the mucosa of the soft palate and the pharynx. 4) Muscular branch: As the glossopharyngeal nerve winds around the stylopharyngeus it supplies this muscle. (Note= This is the only motor branch of the nerve). 5) Tonsillar branch: Supply the tonsil and join the lesser palatine nerves to form a plexus from which fibers are distributed to the soft palate and to the palatoglossal arches. 6) Lingual branch: The lingual branches supply the part of the tongue (mucous membrane) behind the sulcus terminalis. They also supply the vallate papillae. These branches carry fibers for both general sensation and taste. The glossopharyngeal nerve carries fibers that subserve special functions. I. Secretomotor fibers for the parotid gland pass through the glossopharyngeal nerve. The preganglionic neurons concerned are located in the inferior salivatory nucleus which lies at the junction of the pons and medulla just below the superior salivatory nucleus. Preganglionic fibers pass successively through the proximal part of the glossopharyngeal nerve, its tympanic branch, the tympanic plexus and the lesser petrosal nerve to end in the otic ganglion. Postganglionic fibers arising from neurons located in the otic ganglion pass through a nerve connecting the otic ganglion to the auriculotemporal nerve, and then through the auriculotemporal nerve itself. They leave the latter through its parotid branch to reach the parotid gland.
II. Sensory fibers pass through the pharyngeal, tonsilar and lingual branches to supply the mucous membrane of the pharynx, the posterior part of the tongue, the tonsil and the soft palate. III. The glossopharyngeal nerve also contains fibers carrying the sensations of taste from the posterior one third of the tongue (part of the tongue behind the sulcus terminalis, and the vallate papillae). The fibers pass through the glossopharyngeal nerve and its lingual branches to reach the tongue. V) THE OTIC GANGLION The otic ganglion is related functionally to the glossopharyngeal nerve. It is situated just below the foramen ovale medial to the trunk of the mandibular nerve. It is connected to the nerve of the medial pterygoid muscle. The middle meningeal artery and the roots of the auriculotemporal nerve lie close to it. The fibers passing through the otic ganglion are as follows:a) Functionally the ganglion is autonomic and is peripheral ganglion of the cranial parasympathetic outflow. It is the relay station for the secretomotor fibers to the parotid gland. b) Sympathetic fibers reach the ganglion from the plexus on the middle meningeal artery. They pass through the ganglion, without relay, and travel to the parotid gland through the auriculotemporal nerve. c) Motor fibers reach the ganglion through the nerve to the medial pterygoid. These fibers are derived from the motor root of the mandibular nerve. They pass through the ganglion (without relay) and enter branches of the ganglion which supply the tensor tympani and the tensor palate muscles.
VI) CLINICAL CONSIDERATIONS:1. Taste fibers from both the anterior two-thirds and the posterior one third of the tongue have reflex connections with the salivatory nuclei and taste impulses can give rise to an increased rate of salivation-the taste: salivation reflex. 2. Increasing blood pressure stimulates the baroreceptors of the carotid sinus and their reflex connections with the Xth nerve produce a decrease in the heart rate. Inhibition of sympathetic cells in the spinal cord produces peripheral vasodilatation and a decrease in blood pressure. In some individuals the sinus is very sensitive to pressure and syncopal attacks may be induced by light pressure on the neck over the sinus. 3. Changes in the concentration of the blood gases stimulate the chemoreceptors of the carotid body. Their central connection with the respiratory centre influences the respiratory rate. 4. Stimulation of the posterior pharyngeal wall excites glossopharyngeal sensory fibers and initiates the gag reflex. Reflex connections of these sensory fibers with the nucleus ambiguous stimulates the motor fibers which leave the nucleus via the IXth and Xth nerves to the muscles of the pharynx, larynx and soft palate, causing a contraction and elevation of the palate. 5. Isolated lesions of the glossopharyngeal nerve are rare. Lesions which involve the medulla, e.g. syringobulbia, or the nerve on its course towards or within the jugular foramen, e.g. neoplasm of the posterior cranial fossa, meningitis, thrombophlebitis of the internal jugular vein or trauma, usually involving the Xth and XIth cranial nerve also, due to their proximity to the glossopharyngeal nerve.
Involvement of the IXth nerve will produce a loss of gag reflex, loss of sensation of pharynx and the posterior one third of the tongue, loss of taste sensations to posterior one third of the tongue, slight pharyngeal weakness and dysphagia (from paralysis of stylopharyngeus muscle) and possibly loss of salivation from the parotid. VII) CLINICAL TESTING OF THE GLOSSOPHARYNGEAL NERVE:-
Glossopharyngeal nerve is clinically tested as follows: On tickling of posterior wall of pharynx, there is reflex contraction of the throat muscles. No such contractions occur when the ninth nerve is paralysed. Taste sensibility on the posterior one third of the tongue can also be tested. It is lost in ninth nerve lesions Isolated lesions of the ninth nerve are almost unknown. They are usually accompanied by lesions of the vagus nerve. VIII) GLOSSOPHARYNGEAL / VAGOGLOSSOPHARYNGEAL / IDIOPATHIC GLOSSOPHARYNGEAL NEURALGIA Neuralgia is characterized by a sudden paroxysmal pain that is felt radiating down the peripheral distribution of the involved nerve. This pain is episodic, usually with periods of total remission between the painful episodes. The paroxysmal pain is often triggered by a mild, innocuous stimulus. The neuralgia is named according to the nerve involved. Glossopharyngeal neuralgia is similar in character to trigeminal neuralgia but is present in the distribution of the glossopharyngeal nerve and may be present in the distribution of the auricular and pharyngeal branches of the vagus nerve. The pain
is typically severe, transient and stabbing or burning, and located in the ear, base of the tongue, tonsilar fossa, or beneath the angle of the jaw. The pain is unilateral, although 1% to 2% of parents may experience non-simultaneous bilateral pain. The paroxysm of pain usually last seconds to 2 minutes and are proved by swallowing, chewing, talking or yawning. It may relapse and remit like trigeminal neuralgias. The incidence of glossopharyngeal neuralgia is estimated to be 50 to 100 times less than that of trigeminal neuralgia. The neurologic examination is normal. The pathophysiology is thought to be similar to that of idiopathic trigeminal neuralgia. An imaging study as MRI needs to be obtained to exclude symptomatic. Glossopharyngeal neuralgia, which may arise due to posterior fossa tumor, fusiform (dolichoectatic) vertebral or basilar arteries, and vascular anomalies. Additional local causes for the pain such as infection and nasopharyngeal tumor need to be excluded. Effective treatment of glossopharyngeal neuralgia can often be accomplished with the medications used for the treatment of trigeminal neuralgia. In patients who fail medical treatment, a posterior fossa craniectomy with rhizotomy of cranial nerve IX th and the upper rootlets of cranial nerve Xth can effectively treat the condition.
INTRODUCTION. FUNCTIONAL COMPONENTS. COURSE AND DISTRIBUTION OF CRANIAL ROOT. COURSE AND DISTRIBUTION OF SPINAL ROOT. CLINICAL CONSIDERARTIONS. CLINICAL TESTING OF THE ACCESSORY NERVE.
I) INTRODUCTION: The accessory or eleventh cranial nerve arises as two roots, cranial and spinal Spinal accessory Nerve
1) Cranial root: -
2) Spinal root:-
Is accessory to vagus, and is
Has more independent course
distributed through the branches of the latter.
II) FUNCTIONAL COMPONENTS :-
A) The cranial root is special visceral (branchial) efferent: Arises from the lower part of nucleus Ambiguus. The fibers join the vagus nerve and are distributed through its pharyngeal and laryngeal branches to : Soft palate 13
Pharynx Larynx & Possibly the heart.
B) The spinal root is also special visceral efferent: Arises from a long spinal nucleus situated in the lateral part of the anterior grey column of the spinal cord extending between segments C1 to C5. Its fibers supply the sternocleidomastoid and the trapezius muscles.
II) COURSE AND DISTRIBUTION OF CRANIAL ROOT:Origin It emerges in the form of 4 to 5 rootlets which are attached to the posterolateral sulcus of the medulla just below the rootlets of the vagus nerve. The rootlets soon join together to form a single trunk. Within the cranium It runs laterally with the 9th and 10th cranial nerves and the spinal accessory, crosses the jugular tubercle, and reaches the jugular foramen.
Emergence In the jugular foramen, the cranial root unites for a short distance with the spinal root, and again separates from it as it passes out of the foramen.
The cranial root finally fuses with the vagus just below its inferior ganglion, and is distributed through its pharyngeal and recurrent laryngeal branches of the vagus and contribute to the innervations of the muscles of the pharynx and larynx
(except cricothyroid muscle). It is believed that the muscles of the soft palate (except the tensor palati) are supplied exclusively by fibers derived from the accessory nerve. III)
COURSE AND DISTRIBUTION OF SPINAL ROOT:-
Origin Arises from the upper five segments of the spinal cord.
Emergence Emerges in the form of a row of filaments attached to the cord midway between the ventral and dorsal nerve roots.
In the vertebral canal Filaments unite to form a single trunk which ascends in front of the dorsal nerve roots and behind the ligamentum denticulatum.
Enters the cranium The nerve enters the cranium through the foramen magnum lying behind the vertebral artery.
Within the cranium The nerve runs upwards and laterally, crosses the jugular tubercle (with the 9th and 10th cranial nerves) and reaches the jugular foramen.
Leaves the skull 15
Through the middle part of the jugular foramen where it fuses with a short length of the cranial root. It soon separates from the latter and passes out of the for amen.
Extracranial course As the spinal accessory nerve exits from the foramen, it divides into two nerves again, each carrying representative of both roots but still containing a majority of either spinal fibers or cranial fibers. The cranial fibers pass backward and down to supply the trapezius and sternocleidomastoideus muscle. Distribution The spinal accessory nerve supplies:â€˘ Sternomastoid â€˘ Trapezius V) CLINICAL CONSIDERARTIONS:1. Isolated lesions of the cranial root are rare and this portion of the nerve may be involved in lesions which affect the IXth and Xth nerve also. Damage to the vagus nerve, particularly its recurrent laryngeal branches, may affect fibers of the cranial root of the XIth nerve. 2. Lesions involving the spinal root of the nerve, e.g. trauma to, or operation upon, the posterior triangle, results in paralysis and atrophy of Sternomastoid and trapezius muscle with an inability to turn the head away from the affected side and to shrug the shoulder on the affected side. 3. In upper motor neurone lesions, spasticity of the muscles but no atrophy is present and, in unilateral damage, a torticollis (wry neck), may result. 16
4. Torticollis may be congenital, following fibrosis within one Sternomastoid muscle after haematoma, or may be due to local disease or trauma. Spasmodic torticollis, with involuntary neck movements, may be caused by extrapyramidal disease, and may be unresponsive to any treatment other that surgical division of the spinal accessory nerve. VI) CLINICAL TESTING OF THE ACCESSORY NERVE:1. To test the integrity of the cranial root the patient is examined as follows:• Sensations of the pharynx can be tested by touching these areas with a wooden spatula. • The gag reflex can be elicited by touching the posterior wall of the pharynx on either side with the same instrument. • The soft palate can be inspected directly through the open mouth when the patient is asked to say, ‘ah’. In unilateral paralysis of the muscles the paralysed side will not elevate and the uvula will be pulled towards the normal side, i.e. away from the side of the lesion. • Inspection of the larynx and the vocal folds is possible, indirectly, by using a laryngeal mirror. Paralysis of the vocal folds can be seen during attempts at phonation. 2. To test the integrity of the spinal root the patient is examined for atrophy or wasting of Sternomastoid and trapezius muscles and drooping of the shoulder. The power of trapezius is tested by asking :• The patient to shrug his shoulders against resistance, and comparing sides. • Pressing the chin down against resistance outlines the Sternomastoid muscles. Deviation may be noticed towards the affected side during this procedure. 17
• The individual Sternomastoid muscles are tested by rotating the head against resistance to either side. Paralysis or weakness is noticed on an attempt to turn the head away from the affected side.
INTRODUCTION. FUNCTIONAL COMPONENT. COURSE AND RELATIONS. BRANCHES AND DISTRIBUTION. CLINICAL CONSIDERATIONS. CLINAL TESTING OF HYPOGLOSSAL NERVE. I) INTRODUCTION: This is the twelfth cranial nerve. Its fibers are purely motor and they supply the muscles of the tongue. The neurons that give origin to these fibers are located in the hypoglossal nucleus in the medulla. The lower motor neuron fibers of hypoglossal, or twelfth cranial nerve, originate in the nucleus of the hypoglossal nerve, which is 2-cm long column of motor cells located underneath the floor of the fourth ventricle just lateral to the midline. In addition, the hypoglossal nerve carries proprioceptive impulses from the muscles of the tongue to the brain. II) FUNCTIONAL COMPONENT:18
It is a somatic efferent nerve. The fibers arise from the hypoglossal nucleus which lies in the medulla, in the floor of the fourth ventricle deep to the hypoglossal triangle.
III) COURSE AND RELATIONS:Intracranial course The nerve is attached to the anterolateral sulcus of the medulla, between the pyramid and the olive, by 10 to 15 rootlets. At the base of the brain The rootlets run laterally (behind the vertebral artery, and join to form two bundles which pierce the duramater separately near the hypoglossal canal. Leaves the skull The nerve leaves the skull through the hypoglossal canal and lies within the carotid sheath and passes downwards between the internal jugular vein and the internal carotid artery in front of the vagus, deep to the parotid gland Extracranial course It courses forward and is almost horizontal as it reaches a level deep to the angle of the mandible. At the lower border of the posterior belly of the diagastric it curves forwards, hooks round the lower Sternomastoid branch of the occipital artery, crosses the internal and external carotid arteries and passes deep to the posterior belly of the diagastric again to enter the submandibular region.
The nerve then continues forwards on the hypoglossus and genioglossus, 19
deep to the submandibular gland and the mylohyoid, and enters thesubstance of the tongue to supply all the intrinsic and extrinsic muscles of the tongue (except palatoglosssus which is supplied, along with other muscles of the palate, by the cranial accessory nerve )
IV) BRANCHES AND DISTRIBUTION:In addition to its own fibers, the nerve also carries fibers that reach it from spinal nerve C1, and are distributed through it. Hypoglossal nerve
A) Branches containing fibers of
B) Branches of the hypoglossal nerve
the hypoglossal nerve proper.
containing fibers of nerve C1.
1)Meningeal br. 2)Descending br. 3)Branches given to thyrohyoid & geniohyoid muscles. A. Branches containing fibers of the hypoglossal nerve proper. They supply all the intrinsic and extrinsic muscles of the tongue, except the palatoglossus which is supplied by fibers of the cranial accessory nerve through the vagus and the pharyngeal plexus. B. Branches of the hypoglossal nerve containing fibers of nerve C1. These fibers join the nerve at the base of the skull.
1. The Meningeal branch contains sensory and sympathetic fibers. It enters the skull through the hypoglossal canal, and supplies bone and meninges in the anterior part of the posterior cranial fossa. 2. The descending branch continues as the descendens hypoglossi or the upper root of the ansa cervicalis. 3. Branches are also given to thyrohyoid and geniohyoid muscles. V) CLINICAL CONSIDERARTIONS:1. The XIIth nerve may be damaged by trauma at or below its exit from the skull, e.g. skull fracture, upper cervical fracture or dislocation. The hypoglossal nucleus or its central connections may be involved in intracranial lesions, e.g. haemorrhage, tumors, syringobulbia, multiple sclerosis, infections of the posterior cranial fossa, etc. 2. Peripheral damage to the nerve, or damage to its nucleus, causes a flaccid paralysis of the muscles of the tongue on the affected side, atrophy of the paralysed muscles with â€˜wrinklingâ€™ of the tongue on that side, and deviation of the tongue towards the side of the lesion on protrusion. Fasciculation of the affected half of the tongue may also be present.This deviation is due to the unopposed contraction of the contralateral genioglossus, which pulls the base of the tongue forward. Involvement of the hypoglossal nucleus is usually associated with damage to related nerves or medullary structures. 3. Supranuclear damage, e.g. lesions of the corticobulbar tracts, results in a spastic paralysis, without wasting or fibrillation, to the contralateral side of the tongue 4. Hemiparalysis of the tongue may give rise to difficulty with speech, mastication and swallowing.
5. Bilateral lesions of the hypoglossal nerves results in an immobile tongue which can be displaced into the throat, interfering with respiration. Tracheotomy may be required. VI) CLINICAL TESTING OF THE HYPOGLOSSAL NERVE :1. Observation of the tongue may reveal wasting, wrinkling or fasciculation. Deviation of the tongue on protrusion should be noted. 2. The power of the tongue musculature can be tested by asking the patient to push each cheek out with his tongue against resistance. Comparison of both sides can be made.
1) Clinical anatomy for dentistry (dental series) by R.B Longmore and D.A Mcrae. 2) Atlas of human anatomy by inderbir singh. 3) Mc minnâ€™s color atlas of head and neck anatomy by Bari.M.Logan, Patriciar A. Reynolds and Ralph.T.Hutchings.
Published on Apr 28, 2014
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