Spinal Nerves, Dermatomes, and Cranial Nerves Handout for Cranial Nerves.
MICROSURGICAL ANATOMY OF CRANIAL NERVES
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ANATOMY OF CRANIAL NERVES By Dr PANKAJ R PATEL DNB NEUROSURGERY CARE HOSPITALS, HYDERABAD
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Transcript of MICROSURGICAL ANATOMY OF CRANIAL NERVES
ANATOMY OF CRANIAL NERVES
By Dr PANKAJ R PATEL DNB NEUROSURGERY CARE HOSPITALS, HYDERABAD
SENSORY/AFFERENT
OLFACTORY
OPTIC
VESTIBULOCOCHLEAR
MOTOR/EFFERENT
OCCULOMOTOR
TROCHLEAR
ABDUCENS
ACCESSARY
HYPOGLOSSAL
MIXTURE
TRIGEMINAL
FACIAL
VAGUS
GLOSSOPHARYNGEAL
Cranial nerves
Cranial nerves
Exit points -
Trigeminal Nerve (CN V)
• Trigeminal or fifth cranial nerve is the largest of the cranial nerves.
• It is a mixed nerve that consists primarily of sensory neurons.
Sensory nerve FaceMotor nerve Muscles of masticaion & several small muscles
• Lies in the floor of the middle cranial fossa, on the petrous temporal bone.
• It is called trigeminal because it consists of 3 divisions the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).
• It forms the trigeminal ganglion from which its three branches diverge. The trigeminal ganglion corresponds to the dorsal root ganglion
of a spinal nerve.
Trigeminal Nerve Nuclei• The trigeminal nerve has four nuclei: • 1.Main Sensory Nucleus• The main sensory nucleus lies in the posterior part of the pons, lateral to
the motor nucleus . It is continuous below with the spinal nucleus.• 2.Spinal Nucleus• The spinal nucleus is continuous superiorly with the main sensory nucleus
in the pons and extends inferiorly through the whole length of the medulla oblongata and into the upper part of the spinal cord as far as the second cervical segment
• 3.Mesencephalic Nucleus• it composed of a column of unipolar nerve cells situated in the lateral part
of the gray matter around the cerebral aqueduct• 4.Motor Nucleus In the pons medial to the main sensory nucleus
Trigeminal Nerve – Nuclear OriginOne motor and three sensory nuclei.
Sensory Components of the Trigeminal Nerve
• The sensations of pain, temperature, touch, and pressure from the skin of the face and mucous membranes travel along axons whose cell bodies are situated in the trigeminal sensory ganglion .
• The central processes of these cells form the large sensory root of the trigeminal nerve.
• The ascending branches terminate in the main sensory nucleus, and the descending branches terminate in the spinal nucleus.
• The sensations of touch and pressure are conveyed by nerve fibers that terminate in the main sensory nucleus. The sensations of pain and temperature pass to the spinal nucleus
• The sensory fibers of V1 division terminate in the inferior part of the spinal nucleus; the maxillary division in the middle and the mandibular division in the superior part .
• Proprioceptive impulses from the muscles of mastication and from the facial and extraocular muscles are carried by fibers in the sensory root of the trigeminal
nerve that have bypassed the semilunar or trigeminal ganglion .
• The axons of the neurons in the main sensory and spinal nuclei and the central processes of the cells in the mesencephalic nucleus now cross the median plane and ascend as the trigeminal lemniscus to terminate on the nerve cells of the ventral posteromedial nucleus of the thalamus.
• The axons of these cells now travel through the internal capsule to the postcentral gyrus (areas 3, 1, and 2) of the cerebral cortex.
Motor Component of the Trigeminal Nerve
• The motor nucleus receives corticonuclear fibers from both cerebral hemispheres . It also receives fibers from the reticular formation, the red nucleus, the tectum,and the medial longitudinal fasciculus. The cells of the motor nucleus give rise to the axons that form the motor root.
• The motor nucleus supplies the muscles of mastication, the tensor tympani, the tensor veli palatini, and the mylohyoid and the anterior belly of the digastric muscle.
Course of the Trigeminal Nerve• The trigeminal nerve leaves the anterior aspect of the pons as a small
motor root and a large sensory root. The nerve passes forward out of the posterior cranial fossa and rests on the upper surface of the apex of the petrous part of the temporal bone in the middle cranial fossa.
• The large sensory root now expands to form the crescent-shaped trigeminal ganglion, which lies within a pouch of dura mater called the trigeminal or Meckel cave. The ophthalmic, maxillary, and mandibular nerves arise from the anterior border of the ganglion . The ophthalmic nerve (V1) contains only sensory fibers and leaves the skull through the superior orbital fissure to enter the orbital cavity.
• The maxillary nerve (V2) also contains only sensory fibers and leaves the skull through the foramen rotundum.
• The mandibular nerve (V3) contains both sensory and motor fibers and leaves the skull through the foramen ovale.
• The trigeminal ganglion (or Gasserian ganglion, or semilunar ganglion) is a sensory ganglion of the trigeminal nerve (CN V) that occupies a cavity (Meckel's cave) in the dura mater, covering the trigeminal impression near the apex of the petrous part of the temporal bone.
Three major branches emerge from the trigeminal ganglion and each branch innervates a different dermatome :
1. The ophthalmic nerve (VI) passes along the side of the cavernous sinus to pass into the orbit through the superior orbital fissure.
2. The maxillary nerve (V2) passes along the lateral wall of the cavernous sinus to leave the skull through the foramen rotundum in the sphenoid bone.
3. The mandibular nerve (V3) passes out of the skull through the foramen ovale.
• Motor part supplies the 4 muscles of mastication , mylohyoid , anterior belly of digastric , tensor palati and
tensor tympani .• Sensory part carries sensations from the scalp, face , teeth ,
gums and anterior two third of tongue.
Dermatome of Head & Neck OPHTHALMIC NERVE : 1. Cornea2. Skin of forehead3. Scalp4. Eyelids and nose5. Mucous membranes of paranasal sinuses and nasal cavity6. tentorium cerebelli MAXILLARY NERVE :1. Skin of the face over maxilla2. Teeth of the upper jaw3. Mucous membrane of the nose, the maxillary sinus and
palate4. Meninges ACF ,MCF MANDIBULAR NERVE :1. Skin of cheek 2. Skin over mandible and side of head3. Teeth of lower jaw and TMJ4. Mucous membrane of mouth and anterior part of tongue5. Meninges acf anf mcf
Ophthalmic Nerve - CN ( V1) • Origin: Anterior aspect of the pons• Opening to the Skull: Superior orbital fissure• It has 3 main branches : * Frontal * Nasociliary * Lacrimal meningeal
Maxillary Nerve: CN V2 • Origin: Anterior aspect of the pons
• Opening to the Skull: Foramen rotundum
• Compostion: sensory
Infraorbital foreman
It is divided into four groups :
1. Cranium : Middle meningeal (meninges of ant and middle cranial fossa)
2. In the Pterygopalatine Fossa : Zygomatic, Sphenopalatine, Posterior superior alveolar.(upper lip,teeth and gums,palate and nasopharynx)
3. In the Infraorbital Canal : Anterior superior alveolar, Middle superior alveolar.(cheek)
4. On the Face : Inferior palpebral, External nasal, Superior labial.( lateral forhead)
Mandibular Nerve• It is the largest of the 3 divisions of trigeminal nerve. • It is the nerve of the first branchial arch. • Opening to the Skull: Foramen Ovale• Composition : Mixed nerve.• After exit from foramen ovale it(nervous spinosus)
re-enters the skull through f.spinosum.run with MMA supply meninges of and ant. And middle cranial fossa
• Give ant. branch buccal nerve.• Post.branch lingual and auriculotemporal nerve and
inf alveolar
Mental Foramen
innervates the mucosa of the mouth and gums.
innervates the external auditory meatus and portions of the external surface of the tympanic membrane.
provides general sensation to the anterior 2/3 of the tongue
innervate the lower teeth and gums. chin and lower lip
nerve to the masseter m , temporalis m., medial and lateral pterygoids, tensor palati and tensor tympani.
anterior belly of the digastric muscle.
V3
Sensory Branches of Mandibular Division (V3) cont:
Buccal
Auriculotemporal
Lingual n.Mental
Inf. alvolar
Mandibular (V3)
Motor Branch of Mandibular Nerve (V3)
Suprahyoid Muscles• Mylohyoid • Anterior Belly Of Digastric Muscle Chewing
MasseterTemporalis Medial & Lateral
Pterygoid Tensor Palati Tensor Tympani
A: Corneal reflex. B: Visual body reflex
Corneal reflex
• Light touching of the cornea results in blinking of the eyelids. Afferent impulses from the cornea or conjunctiva travel through the v1 division of the trigeminal nerve to the sensory nucleus of the 5th nerve
• Internuncial neurons connect with the motor nucleus of the 7th on both sides through the medial longitudinal fasciculus. 7th supply the orbicularis oculi muscle causes closure of the eyelids.
• Visual Body Reflexes• The automatic scanning movements of the eyes and head that
are made when reading,the automatic movement of the eyes, head, and neck toward the source of the visual stimulus, and the protective closing of the eyes and even the raising of the arm for protection are reflex actions .
• The visual impulses follow the optic nerves, optic chiasma, and optic tracts to the superior colliculi. Here, the impulses are relayed to the tectospinal and tectobulbar tracts and to the neurons of the anterior gray columns of the spinal cord
and cranial motor nuclei.
APPLIED ANATOMY OF TRIGEMINAL NERVE
• Trigeminal neuralgia ( tic douloureux ) is a sensory disorder of CN V that is characterized by sudden attacks of excruciating, intense ,burning or shock-like facial pain that lasts from few seconds to several minutes and can be physically and mentally incapacitating.
• The maxillary nerve is most frequently involved, then the mandibular nerve, and least frequently the ophthalmic nerve.
Trigeminal Neuralgia
• The pain is initiated by touching a sensitive trigger zone of the skin.
• Most cases are still referred to as idiopathic, although many are associated with vascular compression of the trigeminal nerve.(most common by SCA
• Also called the lateral medullary syndrome is a classic clinical demonstration of the anatomy of the fifth nerve.
• A stroke usually affects only one side of the body. If a stroke causes loss of sensation, the deficit will be lateralized to the right side or the left side of the body. The only exceptions to this rule are certain spinal cord lesions and the medullary syndromes .
Wallenberg Syndrome
• In Wallenberg syndrome, a stroke causes loss of pain/temperature sensation from one side of the face and the other side of the body.
• The explanation involves the anatomy of the brainstem. In the medulla, the ascending spinothalamic tract (which carries pain/temperature information from the opposite side of the body) is adjacent to the descending spinal tract of the fifth nerve (which carries pain/temperature information from the same side of the face).
• A stroke that cuts off the blood supply to this area destroys both tracts simultaneously.
• The result is loss of pain/temperature sensation (but not touch/position sensation) in a unique “checkerboard” pattern (ipsilateral face, contralateral body) that is entirely diagnostic.
Clinical evaluation of CN V
• The sensory function is tested by asking the patient to close his or her eyes and respond when feeling a touch,pain,temp
• Compare peri oral to post.face to exclude onion skin pattern• A piece of guaze or test tubes filled with warm and cold fluid
are applied to one cheek and then to the corresponding position on the other side. The testing is then repeated with gentle touch of a sharp pin alternating sides.
• Define 1)organic or inorganic 2)which modality 3)distribution
• The motor function is tested by asking the patient to open the mouth against resistance . Action of both pterygoid muscles keeps the open jaw in the midline. If pterygoid muscles of one side is paralysed , the jaw is deviated to the paralysed side ( Pterygoid muscles of one side pushes the jaw to the opposite side normally ).
• bulk and power of masseter and pterygoids by palpation when clinching of jaw
• For deviation draw line in midline of upper and lower lip• Inability to close the mouth (dangling jaw) suggest
MND,myopathy• Tensor tympani paralysed-difficulty in hearing high notes
reflex
• Corneal• Sternutatory(sneeze)• Jaw jerk
Facial Nerve (CN VII)
Component: Mixed Origin : lower pons Opening to the Skull: Internal acoustic meatus, facial canal, stylomastoid foramen
Function: Motor
o muscles of the face and scalpo Stapedius muscleo Posterior belly of digastrico Stylohyoid muscles
Sensoryo Taste from ant. 2/3 of tongue, from the floor of the mouth and palate
Secretomotoro Submandibular and sublingual salivary glandso Lacrimal glando Glands of nose and palate
• Facial Nerve Nuclei• The facial nerve has three nuclei: (1) the main motor nucleus, (2) the parasympathetic• nuclei, and (3) the sensory nucleus.
• Main Motor Nucleus• The main motor nucleus lies deep in the reticular formation of the lower part of the• pons . The part of the nucleus that supplies the muscles of the upper part• of the face receives corticonuclear fibers from both cerebral hemispheres. The part of• the nucleus that supplies the muscles of the lower part of the face receives only• corticonuclear fibers from the opposite cerebral hemisphere.• These pathways explain the voluntary control of facial muscles. However, another involuntary pathway exists; it is separate and controls mimetic or emotional changes in facial expression. This other pathway forms part of the reticular formation .
• Parasympathetic Nuclei• Parasympathetic nuclei lie posterolateral to the main motor nucleus. They are the superior salivatory and lacrimal nuclei . The superior salivatory nucleus receives afferent fibers from the hypothalamus through the descending autonomic pathways. Information concerning taste also is received from the nucleus of the solitary tract from the mouth cavity.
• Sensory Nucleus• The sensory nucleus is the upper part of the nucleus of the
tractus solitarius and lies close to the motor nucleus . Sensations of taste travel through the peripheral axons of nerve cells situated in the geniculate ganglion on the seventh cranial nerve.
• The central processes of these cells synapse on nerve cells in the nucleus. Efferent fibers cross the median plane and ascend to the ventral posterior medial nucleus of the opposite thalamus and to a number of hypothalamic nuclei.
• From the thalamus, the axons of the thalamic cells pass through the internal capsule and corona radiata to end in the taste area of the cortex in the lower part of the postcentral gyrus
Course of the Facial Nerve• The facial nerve consists of a motor and a sensory root. The fibers of the motor root first travel posteriorly around the medial side of the abducent nucleus .• They then pass around the nucleus beneath the colliculus facialis in the floor of the fourth ventricle and, finally pass anteriorly to emerge from the brainstem .• The sensory root (nervus intermedius) is formed of the central processes of the unipolar cells of the geniculate ganglion. • The two roots of the facial nerve emerge from the anterior surface of the brain between the pons and the medulla oblongata. They pass laterally in the posterior cranial fossa with the vestibulocochlear nerve and enter the internal acoustic meatus in the petrous part of the temporal bone. At the bottom of the meatus, the nerve enters the facial canal and runs laterally through the inner ear. On reaching the medial wall of the tympanic cavity, the nerve expands to form the sensory geniculate ganglion and turns
sharply backward above the promontory. At the posterior wall of the tympanic cavity, the facial nerve turns downward on the medial side of the aditus of the mastoid antrum, descends behind the pyramid, and emerges from the stylomastoid foramen
Branches within facial canal :1. Greater petrosal nerve2. Nerve to the stapedius3. Chorda tympani
Branches immediately below the stylomastoid foramen :4. Posterior auricular5. Diagastric6. Stylohyoid
Branches within the parotid gland :7. Temporal8. Zygomatic9. Buccal10. Mandibular11. Cervical
BRANCHES OF FACIAL NERVE
FUNCTION OF FACIAL NERVES
APPLIED ANATOMY OF
FACIAL NERVE
Facial palsy • Facial palsy is due to the paralysis of facial nerve.
• It is of 2 types – * Upper motor neuron type * Lower motor neuron type
• Upper motor neuron facial palsy is due to the involvement of corticonuclear fibers.
• It is also called as supranuclear type of palsy.
• It leads to paralysis of the contralateral lower part of face below the palpebral fissure.
• The upper part of face is spared because the part of the facial nucleus which supplies it, is innervated by corticonuclear fibers from both the cerebral hemispheres.
• Lower motor neuron palsy is of 2 types :
1. Nuclear paralysis - due to involvement of nucleus of facial nerve, the motor nucleus of facial nerve is close to the abducens nerve which is also usually affected, it leads to paralysis of muscles of the entire face on ipsilateral side.
2. Infranuclear paralysis : This occurs due to involvement of facial nerve.
Bell’s Palsy • Is a lower motor neuron type of facial nerve
involvement.• It has varied etiology eg : exposure to sudden cold,
middle ear infections.• It leads to paralysis of muscles of facial expression.
Bell's palsy is a type of facial paralysis that results in an inability to control the facial muscles on the affected side. They may include muscle twitching, weakness, or total loss of the ability to move one or rarely both sides of the face. Other symptoms include drooping of the eyelid, a change in taste, pain around the ear, and increased sensitivity to sound.
Millard Gubler Syndrome(venral pontine
syndrome)• Abducens nerve palsy on the ipsilateral
side leads to diplopia,int.strabismus
• Infra nuclear type of facial nerve palsy leads flacid paralysis of fascial muscles with loss of corneal reflex
• Contra lateral hemiplegia due to involvement of corticospinal tract
Raymond Foville Syndrome• Due to blockage of basilar artery,in the
region of pons• Paralysis of conjugate occular deviation to
same side of lesion due to pprf infarct• Contralateral hemiplegia, infra nucleus
facial nerve palsy,6th nerve palsy on the same side
Ramsay Hunt Syndrome
• Re activation of herpes zoster in geniculate ganglion
• Triad of I/L facial paralsis,ear pain,vesicles on the face or ear is typical presentation
• Also called herpes zoster oticus
• Facial nerve injured by forceps delivery, fracture of skull, tumour, middle ear infection.
Injury of Zygomatic branch of CN VII
• Leads to paralysis, loss of tone of orbicularis oculi, in the lower eyelid thus the lower eye lid drops.
• As a result, tears do not spread over the cornea and the dry cornea ulcerates – results in corneal scar – impairs vision.
Paralysis of Buccal branch
• It prevents the emptying of food from the vestibule of the cheeks.
• The food lodges in the vestibule and cannot be maintained in position between the teeth for chewing.
Paralysis of Marginal mandibular branch of CN VII
• This may occur when an incision is made along the inferior border of the mandible.
• Injury to this branch results in an unslightly drooping of the corner of the mouth.
Injury of Facial nerve at various sites
Clinical evaluation of Facial nerve
Tested by checking the facial muscles :
1. FRONTALIS: Ask the patient to look upward without moving his head and look for normal horizontal wrinkles of the forehead.
2. ORBICULARIS OCULI: Tight closure of eyes.
3. ORBICULARIS ORIS: whistling and pursing the mouth.
4. DILATOR OF MOUTH: Showing the teeth.
5. BUCCINATOR: Puffing the mouth and then blowing forcibly.
6. PLATYSMA: Forcible pulling of the angle of the mouth downwards and backwards forcing vertical folds of skin on the side of the neck.
• Taste on each half of the anterior two thirds of the tongue can be tested with sugar, salt, vinegar and quinine for sweet, salt, sour and bitter sensation.
Vestibulocochlear Nerve CN (VIII)
• Other Names : Auditory / Acoustic Nerve
• Component : Sensory
• Function: o Vestibular – saccule,scc-Balance, position of heado Cochlear – Organ of Corti – Hearing
• Origin:pons
• Opening to the Skull: Internal acoustic meatus
Vestibulocochlear Nerve
Vestibular nerve nuclei and their central connections
Vestibular Nerve• The vestibular nerve conducts nerve impulses from the
utricle and saccule that provide information concerning the position of the head; the nerve also conducts impulses from the semicircular canals that provide information concerning movements of the head.
• The nerve fibers of the vestibular nerve are the central processes of nerve cells located in the vestibular ganglion, which is situated in the internal acoustic meatus.
• They enter the anterior surface of the brainstem in a groove between the lower border of the pons and the upper part of the medulla oblongata
• The Vestibular Nuclear Comple• Four nuclei may be recognized:• (1) the lateral vestibular nucleus, • (2) the superior vestibular nucleus,• (3) the medial vestibular nucleus, and • (4) 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
• .Efferent fibers from the nuclei pass to the cerebellum through the inferior cerebellar peduncle also descend uncrossed to the spinal cord from the lateral vestibular nucleus and form the vestibulospinal tract In addition, efferent fibers pass to the nuclei of the 3,4,6 nerve through MLF
• These connections enable the movements of the head and the eyes to be coordinated
• so that visual fixation on an object can be maintained. In addition, information received from the internal ear can assist in maintaining balance by influencing the muscle tone of the limbs and trunk.
• ascending fibers also pass upward from the vestibular nuclei to the cerebral cortex to
• the vestibular area in the postcentral gyrus just above the lateral fissure.
• These fibers are thought to relay in the ventral posterior nuclei of the thalamus. The cerebral cortex
• probably serves to orient the individual consciously in space.
Cochlear nerve nuclei and their central connections.
• Cochlear Nerve• The cochlear nerve conducts nerve impulses concerned with sound
from the organ of Corti in the cochlea. The fibers of the nerve enter the anterior surface of the brainstem at the lower border of the pons on the lateral side of the emerging facial nerve and are separated from it by the vestibular nerve
• Cochlear Nuclei• The anterior and posterior cochlear nuclei are situated on the surface
of the inferior cerebellar peduncle . They receive afferent fibers from the cochlea through the cochlear nerve. The cochlear nuclei send axons (second-order neuron fibers) that run medially through the pons to end in the trapezoid body and the olivary nucleus.
• Here, they are relayed in the posterior nucleus of the trapezoid body and the superior olivary nucleus on the same or the opposite side. The axons now ascend through the posterior part of the pons and midbrain and form a tract known as the lateral lemniscus .
• Each lateral lemniscus, therefore, consists of third-order neurons from both sides.
• On reaching the midbrain, the fibers of the lateral lemniscus either terminate in the nucleus of the inferior colliculus or are relayed in the medial geniculate body and pass to the auditory cortex of the cerebral hemisphere through the acoustic radiation of the internal capsule
• The primary auditory cortex (areas 41 and 42) includes the gyrus of Heschl on the upper surface of the superior temporal gyrus. The recognition and interpretation of sounds on the basis of past experience take place in the secondary auditory area..
Course of the vestibulocochlear Nerve
• The vestibular and cochlear parts of the nerve leave the anterior surface of the brainbetween the lower border of the pons and the medulla oblongata .
• They run laterally in the posterior cranial fossa and enter the internal acoustic meatus with the facial nerve. The fibers are the distributed to the different parts of the internal ear
Distribution of the vestibulocochlear nerve.
Clinical examination• History and observation• Whispered voice has been recommeded as a screening test
for hearing assesment• Finger rub test-bedside• Stethoscope –earpiece and chest piece• Ross’ method-6 ft whisper and compare• CALFRAST TEST-70 cm soft rub soundSchwabach tuning fork
test-compare AC,BC with examiner self• Rinne and weber test
Vestibular fuction Vestibulospinal reflex• past pointing• romberg’s test,• Tandem gait• Tandem romberg’s test• Star walking test VOR • Oculocephalic test(doll’s eye test)• Head thrust• Dynamic visual acuity• Caloric tesr(COWS)• nystagmus
Causes of hearing loss
Conductive type• ext,.auditory canal obstruction• Perforation of T.M• Middle ear dis.• Nasopharynx dis.causing blocked eustachian tube SNHL• DIS. Of cochlea –acoustic trauma,meniers dis,infection,presbycusis• DIS. Of cochlear nerve or nuclei-trauma,tumour,infection or toxin
Glossopharyngeal NERVE CN IX
Glossopharyngeal nerve nuclei and their central connections
• Other Name : Hering ’s nerve
• Component : Mixed
• Origin: Medulla oblongata
• Opening to the Skull: Jugular foramen
• Function:• Motor Stylopharyngeus muscle – assists swallowing• Sensory Pharynx Carotis sinus and carotid body Gustatory :- Posterior one third of tongue including circumvallate papillae.• Secretomotor Parotid gland
Glossopharyngeal Nerve Nuclei• The glossopharyngeal nerve has three nuclei: (1) the main motor nucleus, (2) the
parasympathetic nucleus, and (3) the sensory nucleus• Main Motor Nucleus• The main motor nucleus 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• The parasympathetic nucleus is also called the inferior salivatory nucleus • It receives afferent fibers from the hypothalamus through the descending autonomic
pathways. It also is thought to receive information from the olfactory system through the reticular formation. Information concerning taste also is received from the nucleusof the solitary tract from the mouth cavity.
• The efferent preganglionic parasympathetic fibers reach the otic ganglion through the• tympanic branch of the glossopharyngeal nerve, the tympanic plexus, and the lesser• petrosal nerve . The postganglionic fibers pass to the parotid salivary• gland
• Sensory Nucleus• The sensory nucleus is part of the nucleus of the tractus solitarius . Sensations of taste travel through the peripheral axons of nerve cells situated in the ganglion on the glossopharyngeal nerve. The central processes of these cells synapse on nerve cells in the nucleus.• Efferent fibers cross the median plane and ascend to the ventral group of nuclei of the opposite thalamus and a number of hypothalamic nuclei.• From the thalamus, the axons of the thalamic cells pass through the internal capsule and corona radiata to end in the lower part of the postcentral gyrus.• Afferent impulses from the carotid sinus, a baroreceptor situated at the bifurcation of the common carotid artery, also travel with the glossopharyngeal nerve. They terminate in the nucleus of the tractus solitarius and are connected to the dorsal motor nucleus of the vagus nerve. The carotid sinus reflex that involves the glossopharyngeal and vagus nerves assists in the regulation of arterial blood pressure
Course of the Glossopharyngeal Nerve
• Course of the Glossopharyngeal Nerve• The glossopharyngeal nerve leaves the anterolateral surface of the upper part of the medulla oblongata as a series of rootlets in a groove between the olive and the inferior• cerebellar peduncle ). • It passes laterally in the posterior cranial fossa and leaves the skull through the jugular
foramen.• The superior and inferior glossopharyngeal sensory ganglia are situated on the nerve here.
The nerve then descends through the upper part of the neck in company with the internal jugular vein and the internal carotid artery to reach the posterior border of the stylopharyngeus muscle, which it supplies.
• The nerve then passes forward between the superior and middle constrictor muscles of the pharynx to give sensory branches to the mucous membrane of the pharynx and the posterior third of the tongue .
1. Communicating branch - a twig to the ganglion of vagus nerve - a twig to auricular branch of vagus nerve.
2. Tympanic branch - Lesser petrosal nerve - carry pre-ganglionic
parasympathetic secretomotor fibres to parotid gland . - twigs to tympanic cavity, auditory tube
Branches of Glossopharyngeal nerve
3. Carotid branch – supplies the carotid sinus
4. Pharyngeal branch - form plexus with branches of vagus and sympathetic .
5. Branch to stylopharyngeus
6. Tonsillar branches - tonsil and soft palate
7. Lingual branches - taste and general sensation from posterior one third of tongue .
APPLIED ANATOMY OF GLOSSOPHARYNGEAL
NERVE
• Complete lesion of the glossopharyngeal nerve results in the following :
1. Loss of taste and common sensations over the posterior one third of the tongue.
2. Difficulty in swallowing3. Loss of salivation from the parotid gland4. Unilateral loss of gag reflex • Complete lesion of glossopharyngeal nerve is
rare in isolation. There is often involvement of vagus nerve.
Glossopharyngeal Neuralgia
• It is known as tic douloureux of CN IX or Cranial mononeuropathy IX .
• It is a condition in which there are repeated episodes of severe pain in the tongue, throat, ear and tonsils which can last from few seconds to few minutes.
• It is believed to be caused by irritation of the ninth cranial nerve.
• The sudden intensification of pain is of a burning or stabbing nature.
• Paroxysms of pain are initiated by swallowing, protruding the tongue, talking or touching the palatine tonsil.
• Pain paroxysms occur during eating when trigger areas are stimulated.
Clinical Evaluation Of Glossopharyngeal Nerve
• Ninth nerve is tested by tickling the posterior wall of pharynx. There is reflex contraction of pharyngeal muscles called gag reflex .
• In IX nerve paralysis there is no such contraction.
Vagus Nerve (CN X)
• Vagus nerve is a mixed nerve.
• Containing approximately 80% sensory fibers.
• It supplies :
Organs of voice and respiration with both motor and sensory fibres .
Pharynx (except stylopharyngeus), oesophagus, stomach and heart with motor fibres.
One muscle of the tongue (palatoglossus).The muscles of the soft palate (except tensor veli palatini ).
• It is the most extensive cranial nerve, consisting of many branches.
COURSE OF VAGUS NERVE• The nerve runs from the lower brainstem through the
base of the skull to travel in the neck with the carotid artery and jugular vein.
• It then penetrates the chest to travel to the heart and lungs.
• It continues on to the abdomen where it breaks into a
network of nerves to the abdominal organs.
• Supplies motor and sensory parasympathetic fibres to pretty much everything from the neck down to the first third of the transverse colon.
• It is involved in, amongst other things, such as heart rate, gastrointestinal peristalsis, sweating, and speech (via the recurrent laryngeal nerve) and also the controls a few skeletal muscle of the pharynx and larynx:
Levator veli palatini muscle Salpingopharyngeus muscle Stylopharyngeus muscle Palatoglossus muscle Palatopharyngeus muscle Superior, middle and inferior pharyngeal
constrictors
CLINICAL ANATOMY OF VAGUS NERVE
• Lesion Of Vagus Nerve Leads To :
DysphagiaHoarsenessUvula points away from the affected side Loss of gag and cough reflex
Accessory Nerve (CN XI)
• Component: Motor
• Function:
Cranial root o Muscles of soft palate (except tensor veli palatini)o Muscles pharynx (except styopharyngeus)o Muscles of larynx (except cricothyroid)
Spinal root o Sternocleidomastoid o Trapezius muscle
• Origin: Medulla oblongata
• Opening to the Skull: Jugular foramen
• The sternocleidomastoid muscle turns the head and the trapezius muscle braces the shoulder and rotates the scapula during elevation of the upper limbs.
ASSESSING X & XI CRANIAL NERVES
• CN X &XI can be assessed together by testing the gag reflex, palatal movement and sensation.
– Touching the pharynx with an orange stick tests pharyngeal sensation (9th nerve) and the gag reflex (9th and 10th nerve). On phonation the soft palate should rise symmetrically in the midline (10th nerve).
• CN XI can be tested by assessing the power of the sternocleidomastoid and the trapezius muscles i.e. turning the head and shrugging the shoulders.
APPLIED ANATOMY OF ACCESSARY NERVE
• Lesion may result the followings :
Shoulder droop
Weakness turning head to opposite side
Hypoglossal Nerve (CN XII)
• Component : Motor.
• Supplies : Muscles of the tongue except the palatoglossus
• Fibers arises : From the hypoglossal Nucleus which lies in the Medulla, in the floor of the fourth verticle
• Opening to the skull : Hypoglossal canal.
• After coming out of the cranial cavity the nerve lies deep to the internal carotid artery and the ninth, tenth and eleventh cranial nerves.
• Finally the nerve ends by dividing into terminal branches.
• Some fibers of the first cervical nerve join the hypoglossal nerve and are distributed through its branches.
BRANCHES OF HYPOGLOSSAL NERVE
1. Muscular branches : These are branches of the hypoglossal nerve proper and
supply all the muscles of the tongue expect palatoglossus which is supplied by the cranial root of accessory nerve via the pharyngeal plexus.
2. Branches of the Hypoglossal nerve containing C1 fibers :
* Meningeal branch – It supplies the duramater of posterior cranial fossa.
* Descendens hypoglossi or upper root of ansa cervicalis – it arises from the nerve as it crosses the internal carotid artery. It runs downwards to join the inferior root of ansa cervicalis.
* Nerve to thyrohyoid
3. Nerve to geniohyoid
APPLIED ANATOMY OF HYPOGLOSSAL NERVE
Injury to the Hypoglossal nerve
• The hypoglossal nerve accompanies the tonsillar artery on the laterial wall of the pharynx and this wall is vulnerable to injury during tonsillectomy.
• Injury to CN twelve paralyses the ipsilateral half of the tongue. After some time the tongue atrophies, making it appear shrunken and wrinkled.
• When the tongue is protruded, its tip deviates towards the paralysed side because of the unopposed action of the genioglossus in the normal side of the tongue.
Clinical Evaluation Of Hypoglossal Nerve
• The hypoglossal nerve is tested clinically by asking the patient to protrude his tongue. Normally the tongue is protruded straight forward. If the nerve is paralysed, the tongue deviates to the paralysed side.
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