Saturday, November 7, 2009
NUCLIE OF THE CRANIAL NERVES
1st & 2nd Cerebral cortex
3rd & 4th Midbrain
5th, 6th, 7th, 8th Pons
9th, 10th, 11th, 12th Medulla Oblongata
PURE SENSORY NERVES
1st Olfactory nerve:
Sense of smell
2nd Optic nerve:
Sense of vision
8th Vestibulocochlear nerve:
Balance & Hearing
PURE MOTOR NERVES
3rd Occulomotor :
It is motor to all the extra ocular muscles of eye except Superior Oblique and Lateral Rectus Muscle. It is also supplying ciliary muscles and sphincter pupillae with parasympathetic fibers.
4th Trochlear :
Motor to Superior oblique
Motor to Lateral Rectus
Motor to Sternomastoid and Trapezius muscles
Motor to muscles of tongue
MIXED MOTOR AND SENSORY NERVES
Motor to muscles of mastication
Sensory to face, anterior part of head and inside mouth.
7th Facial :
Motor to Muscles of facial expression and Stapedius muscle
Sensory to Part of external ear and taste to anterior two thirds of tongue.
9th Glossopharyngeal :
Motor to Stylopharyngeus
Sensory to Pharynx, Soft palate; Taste to Posterior one third of the tongue.
Motor to muscles of Pharynx, soft palate and larynx.
NERVES CARRYING PARASYMPATHETIC FIBERS
3rd Occulomotor :
Ciliary muscles and Sphincter Pupillae
Thorax & Abdomen
Friday, November 6, 2009
Bundles of these nerve fibers pass through openings in the cribriform plate of ethmoid bone and end in the olfactory bulb in the anterior cranial fossa.
Emerging from the posterior end of olfactory bulb is a white band the olfactory tract which passes backward to the olfactory area of cerebral cortex.
PRIMARY OLFACTORY CORTEX
The second order neurons (mitral cells) project centrally together with pyramidal cells of olfactory nucleus down olfactory tracts and stria to Primary olfactory cortex (medial temporal lobe) and ipsilateral amygdaloid body anterior perforated substance and septial area.
The primary olfactory cortex has numerous connections with hypothalamus reticulatr system, limbic lobe.
TESTING THE SENSE OF SMELL
· Check that nasal passages are clear
· Test sense of smell for each nostril separately
· Occlude one nostril by digital pressure
· Ask patient with closed eyes to sniff and identify the substance
It means loss of sense of smell; commonest cause is obstruction of nasal passages. If due to neurological lesion it may be due to
· Head injury
· Tumors of anterior cranial fossa
· Tuberculous meningitis
It is the perversion of smell. Offensive smells are perceived as pleasant and vice versa.
Psychogenic in origin
Sometimes occur in temporal lobe palsy.
The optic nerve arises from cells of the ganglionic layer of retina.
The optic nerve leaves the eye ball in the orbital cavity passes through the optic canal to enter the middle cranial fossa.
It unites with the optic nerve of opposite side to form the optic chiasma. In the optic chiasma the fibers from the medial half of retina cross the midline and enter optic tract of opposite side
Fibers of lateral half pass posteriorly to the same side tract.
Most fibers of optic tract terminate by synapsing with the nerve cells in the lateral Geniculate body (a small projection from posterior thalamus)
A few fibers pass to pretectal nucleus and superior colliculus of midbrain however are concerned with light reflexes.
The axons of nerve cells of lateral geniculate body pass posteriorly as optic radiation and terminate in visual cortex of cerebral hemisphere.
EFFECT OF LESION OF DIFFERENT PARTS OF VISUAL PATHWAY
LESION AT RETINA
Scotoma (small area of blindness)
LESION OF THE OPTIC NERVE
Total loss of vision in one eye; consensual reflex is retained
LESION OF OPTIC CHIASMA
a) Central Lesion
b) Bilateral peripheral Lesion
LESION OF OPTIC TRACT, LATERAL GENICULATE BODY AND OPTIC RADIATION
Homonymous hemianopia on opposite side without macular sparing. Lesions of optic radiation usually produce quadrantic visual defects
LESION OF THE VISUAL CORTEX
Homonomous hemianopia with macular sparing
It supplies the following extrinsic muscles of the orbit
Levator palpebrae superioris
Superior, Medial, Inferior Rectus
Sphincter pupillae and Ciliary muscles with parasympathetic fibers. (Arising from Edinger Westphal nucleus)
Somatic Efferent for the movements of eye ball. Fibers arise from the Occulomotor nucleus which is situated in ventromedial part of central grey matter of the midbrain at the level of superior colliculus.
General Visceral Efferent (parasympathetic), for contraction of the pupil and accommodation. Fibers arise from the Edinger Westphal nucleus (that lies in mid brain close to Occulomotor nucleus) passes through the Occulomotor nerve to the ciliary ganglion to supply Sphincter pupillae and ciliary muscle.
General Somatic Afferent for the proprioceptive impulses from the muscles of the eyeball. These impulses are relayed to the mesencephalic nucleus of trigeminal nerve.
It emerges from the anterior aspect of midbrain medial to the cerebral peduncle, passes close to and between posterior cerebral and superior cerebellar arteries, runs forward in the lateral wall of cavernous sinus and divide into the superior and inferior ramus.
It enters the orbit through the superior orbital fissure.
Supply superior rectus muscle, then it pierces and supplies overhanging levator palpebrae superioris.
It enters the orbit, gives off branches to inferior rectus, medial rectus, and inferior oblique.
Nerve to inferior oblique gives off a branch that passes to the ciliary ganglion and carries parasympathetic fibers to sphincter pupillae and ciliary muscles
In complete and total paralysis of 3rd nerve eye cannot move upward, downward or inward..It results in ptosis (i.e. drooping of the upper eyelid), lateral squint, dilation of the pupil; loss of accommodation; slight proptosis (i.e. forward projection of the eye); diplopia (double vision)
External Strabismus or Lateral Squint
At rest eye looks laterally because of activity of lateral rectus and downwards because of superior oblique.
SUPRANUCLEAR PARALYSIS OF 3rd NERVE
It causes loss of conjugate movement of eyes
A midbrain lesion causing contra lateral hemiplagia and ipsilateral paralysis of 3rd nerve is known as Weber’s Syndrome.
SQUINT OR STRABISMUS
It may be concomitant or paralytic.
Concomitant squint is congenital; there is no limitation of movement or no diplopia.
In paralytic squint movement of eye ball is limited, diplopia and vertigo are present. The head is turned in the direction of function of paralyzed muscle. There is false orientation of field of vision.
Patient sees double
Drooping of upper eyelid due to paralysis of levator palpebrae superioris.
LOSS OF ACCOMODATION
Pupil is widely dilated and non reactive to light because of paralysis of sphincter pupillae and unopposed action of dilator pupillae (supplied by Sympathetic)
· It is a peripheral parasympathetic ganglion placed in the course of occulomotor nerve.
· It lies near the apex of the orbit between optic nerve and lateral rectus.
· It has motor, sensory and sympathetic roots
It arises from nerve to inferior oblique, contains preganglionic fibers that begin in Edenger Westphal nucleus.
The fibers relay in ganglion, pass through short ciliary nerves and supply sphincter pupillae and ciliaris muscle .
It comes from the nasociliary nerve contains sensory fibers from eyeball.
The fibers do not relay in the ganglion.
It arises from the internal carotid plexus, contains post ganglionic fibers arising in the superior cervical sympathetic ganglion. The fibers do not relay in the ciliary ganglion. They pass out of the ganglion in short ciliary nerves and supply the blood vessels of the eye ball. They may also supply dilater pupallae.
Ganglion gives 8 – 10 short Ciliary nerves that divide to 15 – 20 branches. They pierce sclera around the entrance of optic nerve; contain fibers from all the three roots of the ganglion.
It is the most slender of the cranial nerves
It supplies Superior Oblique Muscle in the orbit
Somatic Efferent for movement of the eye ball.
General Somatic Afferent for Proprioceptive impulses from superior oblique muscle. These impulses are relayed to the mesencephalic nucleus of the trigeminal nerve.
It emerges from posterior surface of the midbrain just below the inferior colliculi, then curves forward around lateral side of cerebral peduncle, runs forward in the lateral wall of cavernous sinus slightly below the occulomotor nerve. It enters the orbit through superior orbital fissure, runs forward and medially across the origin of levator palpebrae superioris and enter the superior oblique muscle.
In case of paralysis of the nerve there double vision on looking straight down. This is because the superior oblique is paralyzed and eye turns medially as well as downwards. Vision is single so long as the eye looks above the horizontal plane.
The patient will adopt a compensatory head tilt.
Isolated nerve lesions are not common.
It’s a small motor nerve that supplies the lateral rectus of eye ball.
Somatic Efferent for lateral movements of the eye ball.
General Somatic Afferent for Proprioceptive impulses from the lateral rectus muscle. These impulses reach the mesencephalic nucleus of trigeminal nerve.
Isolated lesions are common.
In case of paralysis of this nerve eye ball cannot be turned laterally when looking straight ahead the lateral rectus is paralyzed and unopposed medial rectus pulls the eye ball medially causing INTERNAL STRABISMUS or MEDIAL SQUINT or CONVERGENT STRABISMUS
It contains both Sensory & Motor fibers
Sensory fibers to Skin of
· Nasal Cavity
· Para nasal Sinuses
Motor fibers to
· Muscles of Mastication
· Tensor TympaniTensor Veli palatine
· Main sensory nucleus of the trigeminal nerve lies in the upper part of the pons.
· The Spinal nucleus of trigeminal nerve descends from the main nucleus into the medulla. It reaches the upper two segments of the spinal cord.
· The mesencephalic nucleus of the trigeminal nerve extends upwards from the main sensory nucleus into the midbrain.
These nuclei receive the following fibers
· Exteroceptive sensations (Touch, pain, temperature) from the skin of face through the trigeminal nerve.
· Proprioceptive sensations from muscles of mastication reach the mesencephalic nucleus through the trigeminal nerve.
Special Visceral Efferent:
· Motor nucleus of the trigeminal nerve lies in the upper part of pons. It supplies the muscles of mastication through the mandibular nerve.
It emerges from anterior surface of pons by a large sensory and a small motor root. (Motor root medial to sensory root)
Nerve passes out of posterior cranial fossa below the superior petorsal sinus and carries with it a pouch derived from meningeal layer of dura matter.
On reaching the apex of petrous part of temporal bone in the Middle Cranial Fossa the large Sensory root expands to form trigeminal (Gasserian) ganglion.
Ganglion lies in the pouch of the dura matter called Trigeminal Cave.
The motor root lies below the ganglion and is completely separate from it.
Anterior border of the ganglion gives rise to
OPHTHALMIC, MAXILLARY, MANDIBULAR NERVES
· Purely Sensory
· Smallest division of trigeminal nerve
· Runs forward in the lateral wall of Cavernous Sinus below the Occulomotor and Trochlear nerve
· Divides into 3 branches :
Lacrimal, Frontal and Nasociliary
They enter the orbital cavity through the Superior Orbital Fissure.
Arise in the lateral wall of Cavernous Sinus passes through Superior Orbital Fissure to enter the orbit moves on the lateral wall along the upper border of lateral rectus. Here it is joined by branch of zygomaticotemporal nerve (carries parasympathetic secretomotor fibers from Greater Petorsal nerve which is branch of facial nerve ) that later leaves it The nerve supplies Lacrimal gland. (Its own fibers to the gland are sensory)
It ends by supplying skin & Conjunctiva of lateral part of upper eyelid.
Arise in the lateral wall of Cavernous Sinus passes through Superior Orbital fissure to enter the orbit. In the orbit it passes on the Superior surface of levator palpebrae superioris (between muscle and the roof ). It divides in to two branches
· Passes through supraorbital notch or foramen
i. Skin of forehead lateral to area by Supratrochlear
ii. Mucous membrane of frontal sinus
iv. Skin of Central part of upper eyelid.
· Passes above pulley for Superior Oblique
· Wind around the upper margin of orbital cavity
i. Skin of forehead above root of nose
ii. Skin & Conjuctiva of upper eyelid (medial part)
Arise in the lateral wall of Cavernous Sinus passes through the Superior Orbital Fissure above the ophthalmic artery and optic nerve to the medial wall of orbital cavity along the upper margin of medial rectus, ends at the anterior Ethmoidal foramen by dividing into
Anterior Ethmoidal nerve
Communicating Branch to Ciliary Ganglion:
Sensory fibers from the eye ball pass to Ciliary ganglion via short Ciliary nerves without interruption and join the Nasociliary by means of communicating branch.
Long Ciliary Nerve:
· Two or three in number
· Arise from Nasociliary nerve as it crosses the optic nerve
· It contains sympathetic fibers for dilator pupale muscle
· It passes forward with Short Ciliary Nerve pierces the sclera CLOSE TO OPTIC and continues forward between sclera and choroids to reach the Iris
Posterior Ethmoidal Nerve:
It passes through the posterior Ethmoidal foramen to supply the Ethmoidal and Sphenoidal air sinuses
It passes below the pulley and supply the Conjuctiva and skin of medial part of upper eyelid and the adjacent part of nose
Anterior Ethmoidal Nerve:
It passes through anterior Ethmoidal foramen to anterior cranial fossa at the upper surface of cribriform plate and then through slit like opening on side of crista gali pass to the nasal cavity gives two Internal nasal branches MEDIAL & LATERAL that supply area of mucous membrane and then it appears on the face as EXTERNAL NASAL BRANCH at lower border of nasal bone, Supplies skin of nose down as far as the tip.
· Purely Sensory
· It runs forward along the lower part of wall of cavernous sinus
· It leaves the skull through foramen rotundum to enter the pterygopalatine fossa.
· The nerve crosses the fossa and enters the orbit through the inferior orbital fissure. The nerve is now called as Infraorbital nerve.
· It runs forward in the floor of the orbit first in the infraorbital groove and then infraorbital canal.
· Appears on the face through infraorbital foramen.
· MENINGEAL BRANCH
Supply dura in the Middle Cranial Fossa
BRANCHING NERVES IN THE PTERYGOPALATINE FOSSA:
· GANGLIONIC BRANCHES
Two short nerves hold up the pterygopalatine ganglion in the pterygopalatine fossa.
They contain sensory fibers that without interruption have passed through the ganglion from the nose, palate and pharynx.
They also contain post ganglionic parasympathetic fibers that are going to the lacrimal gland.
· POSTERIOR SUPERIOR ALVEOLAR NERVE:
Arise in the pterygopalatine fossa pass down on the back of maxilla and pierce its posterior surface. Supply
Upper Molar Teeth
Adjoining parts of gum and cheek.
· ZYGOMATIC NERVE
Arise in pterygopalatine ganglion and enter the orbit through the inferior orbital fissure, ascends on the lateral wall of orbit give two branches that supply skin of face.
It passes on the face through a small foramen on lateral side of zygomatic bone.
Supply the Skin over the prominence of cheek.
Emerge on the temporal fossa through a small foramen on the posterior surface of zygomatic bone
Supply skin over temple.
· INFRAORBITAL NERVE
i. Middle Superior Alveolar Nerve
Arise from the nerve in the infraorbital groove, descend in the lateral wall of maxillary sinus.
Supply upper molar and adjoining parts of gums & cheek.
ii. Anterior Superior Alveolar Nerve
Arise in the infraorbital canal, descends in anterior wall of maxillary sinus.
Supply Upper Canine & Incisor
Small terminal branch supplies Lateral Wall & Floor of Nose.
· PALPEBRAL: Skin of lower eyelid
· NASAL: Side of nose
· LABIAL: Mucous membrane of upper lip
Also large area of skin of face.
It is the largest parasympathetic peripheral ganglion.
THE MOTOR OR PARASYMPATHETIC ROOT
Preganglionic secretormotor fibers arise in lacrimal nucleus of facial nerve then in its greater petorsal branch & then nerve of pterygoid canal that enters the posterior surface of ganglion.
Postganglionic fibers are scretromotor to
Mucous glands of nose
Postganglionic fibers reach maxillary nerve by one of its ganglionic branches, run in zygomaticotemporal and then to lacrimal.
Others in palatine nerve & nasal nerve to palatine and nasal glands.
Sympathetic root is derived from nerve on pterygoid canal.
Postganglionic fibers in superior cervical sympathetic ganglion that pass through the internal carotid plexus & deep petorsal nerve & nerve of pterygoid canal.
They pass through the ganglion without rely and supply
Mucous membrane of nose
It is from maxillary nerve without relay.
They pass through Inferior Orbital fissure and supply Periosteum of the Orbit and Orbitalis muscle. They are actually the branches of maxillary and carry parasympathetic and sympathetic fibers from the ganglion.
Greater and lesser palatine nerve supply mucous membrane of palate, tonsil and nasal cavity
Enter through sphenopalatine foramen
Lateral posterior superior nasal nerve
Medial posterior superior nasal nerve
Nasopalatine largest descending up to anterior part of hard palate through incisive foramen.
It supplies mucous membrane of roof of nasal part of phyrnx.
· Motor & Sensory nerve
· Largest division of Trigeminal Nerve
· Large sensory nerve leaves the lateral part of trigeminal ganglion, pass almost at once through Foramen Ovale
· Small motor root passes beneath the ganglion
· Immediately after emerging motor root joins sensory root
· The Mandibular nerve now descends & divides into
Ø Small anterior division
Ø Large posterior division
FROM MAIN TRUNK
· MENINGEAL BRANCH
It enters the skull through foramen ovale and supply meningies in Middle Cranial Fossa.
· NERVE TO MEDIAL PTERYGOID
It’s a small branch that supplies to pterygoid muscle.
Two branches pass to otic ganglion without interruption to supply Tensor tympani & Tensor veli palatine.
FROM ANTERIIOR DIVISION
Anterior division gives four branches including
Three Motor Branches
One Sensory Branch
They are described as follows
· MASSETERIC BRANCH:
It runs laterally to supply the massetor muscle.
·TWO DEEP TEMPORAL BRANCHES:
They run upward and enter deep surface of
·NERVE TO LATERAL PTERYGOID
It enters deep surface of the muscle and supplies it.
It is the sensory nerve. It emerges on the cheek from the anterior border of masseter.
Skin over cheek
The mucous membrane lining the cheek.
Buccal nerve does not supply the buccinator.
FROM POSTERIOR DIVISION
· Two Sensory
· One containing sensory as well as motor fibers (The Inferior alveolar nerve.
· AURICULOTEMPORAL NERVE:
Two roots embrace the Middle Meningeal artery, run backward and ascend behind TMJ in accompany with superficial temporal vessels, receive postganglionic parasympathetic secretormotor fibers from otic ganglion and convey to parotid gland; in front of auricle supply skin of
External auditary meatus
Parotid gland (sensory)
Skin of Scalp
· LINGUAL NERVE
It is sensory to anterior 2/3rd of tongue and floor of mouth.
It runs down anterior to Inferior alveolar nerve passes forward and medially beneath lower border of superior constrictor muscle, lateral to the lower third molar runs forward on the lateral surface of hyoglossus in submandibular region. At lower border of lateral pterygoid it is joined by Chorda tympani and also by a branch from Inferior alveolar nerve/
· INFERIOR ALVEOLAR NERVE
It has motor and sensory nerve fibers.
It descends on the lateral surface of sphenomandibular ligament, enters the mandibular canal through the mandibular foramen runs forward below the teeth, emerges through the mental foramen.
Mental nerve supplies lower lip and chin
It is branch of Inferior alveolar nerve.
It arises just above mandibular foramen, runs forward on the medial surface of body of mandible below the Mylohyoid line superficial to mylohyoid muscle.
It supplies Mylohyoid muscle & anterior belly of digastric muscle.
Communicating Branch To Lingual Nerve.
The otic ganglion is a small parasympathetic ganglion that is functionally associated with the Glossopharyngeal nerve. It is situated just below foramen ovale in the infratemporal fossa and is medial to the mandibular nerve. The ganglion adheres to the nerve to medial pterygoid, but functionally it is completely separate from it
The Motor or Parasympathetic Root
The preganglionic parasympathetic fibers originate in the inferior salivatory nucleus of the Glossopharyngeal nerve. They leave the Glossopharyngeal nerve by its tympanic branch and then pass via the tympanic plexus and the lesser petorsal nerve to the otic ganglion. Here the fibers synapse and the postganglionic fibers leave the ganglion and join the auriculotemporal nerve. They are conveyed by this nerve to the parotid gland and serve as secretomotor fibers.
The Sympathetic Root
It is derived from the plexus on the middle Meningeal artery. It contains post ganglionic fibers arising in the superior cervical sympathetic ganglion. The fibers pass through the ganglion without relay and reach the parotid gland via auriculotemporal nerve. They are vasomotor in function.
The Sensory Root
It comes from the auriculotemporal nerve and is sensory to the parotid gland.
· Trigeminal Neuralgia
Episodic facial pain is the most common disease of the 5th nerve. In common idiopathic variety, there are no signs. If signs are present, it is likely that there is structural lesion e.g. multiple sclerosis, tumor involving the 5th nerve. Herpes zoster commonly affects the ophthalmic division and postherpatic neuralgia may occur. There will be a scar and sensory loss over the forehead. The ophthalmic branch is not involved in idiopathic trigeminal neuralgia.
· Fifth nerve is involved in cerebello-pontine angle tumors along with 7th and 8th cranial nerves and cerebellum.
· Ophthalmic division is involved in the lesions of cavernous sinus along with 3rd , 4th and 6th cranial nerves.
· Bilateral motor paralysis may occur in bulbar palsy (there is wasting of muscles of mastication and fasciculations are present) and pseudobulbar palsy (jaw jerk is brisk).
It has a medial motor root and a lateral sensory root, the nervous intermedius.
· Nucleus of the facial nerve lies in the lower part of Pons supplies various muscles innervated by facial nerve. The part of nucleus that supplies muscles of the upper part of the face receives corticonuclear fibers from the motor cortex of both the right and left sides. In contrast the part of nucleus that supplies muscles of the lower part of the face receive corticonuclear fibers only from the opposite side of cerebral hemisphere.
· Lacrimatory nucleus lies near the salivatory nuclei gives fibers that pass through facial nerve and its branches relay in the pterygopalatine ganglion and supply the lacrimal gland.
Supplies Muscles of face, scalp, auricle, buccinator, platysma, Stapedius, stylohyoid & posterior belly of diagastric
It carries the taste fibers from anterior two thirds of tongue, floor of mouth and palate.
It also conveys parasympathetic secretromotor fibers to Submandibular and sublingual salivary glands, lacrimal gland and glands of nose and palate.
The two roots of facial nerve emerge from the anterior surface of brain between the pons and medulla oblongata. They pass laterally forward in the posterior cranial fossa with the Vestibulocochlear nerve to the opening of internal acoustic meatus. At the bottom of the meatus the nerve enters the facial canal runs laterally above the vestibule of labyrinth until it reaches the medial wall of tympanic cavity. (Middle ear)Here the nerve expands to form sensory Geniculate ganglion. The nerve then bends sharply backwards above the promontory, on arriving at the posterior wall of the middle ear, it curves downward. On the medial side of the aditus of the mastoid antrum. It descends in the posterior wall of middle ear, behind the pyramid and finally emerges through the stylomastoid foramen.
The nerve emerges on the superior surface of petrous part of temporal bone and runs forward in a groove. It runs below the trigeminal ganglion and enters the foramen lacerum.
It is here joined by the deep petorsal nerve from sympathetic plexus on the Internal Carotid Artery and forms nerve of pterygoid canal. This passes forward and enters the pterygopalatine fossa where it ends in the pterygopalatine ganglion.
THE NERVE TO STAPEDIUS
It arises from the facial nerve as it descends in the facial canal behind the pyramid. It supplies the muscle with in the pyramid.
It arises from the facial nerve above the stylomastoid foramen. It enters the middle ear close to posterior border of tympanic membrane. It then runs forward over the tympanic membrane and crosses the root of the handle of the malleus. It lies in the interval between the mucous membrane and the fibrous layer of tympanic membrane.
The nerve leaves the middle ear through petrotympanic fissure and enters infratemporal fossa where it joins the lingual nerve. Chorda tympani contain many taste fibers from the mucous membrane covering the anterior two thirds of tongue. (not the vallate papillae)
Taste fibers are the peripheral processes of the cells in the Geniculate ganglion.
Parasympathetic secretomotor fibers
The nerve also contains pre ganglionic parasympathetic secretomotor fibers that reach the Submandibular ganglion and are there relayed to the Submandibular and sublingual salivary gland.
As the nerve runs forward in the substance of parotid gland. It divides into 5 terminal branches
It arises just below the stylomastoid foramen. It ascends between the mastoid process and the external acoustic meatus and supplies the
· Auricularis posterior
· The Occipitalis
· Intrinsic muscles on the back of the auricle
It arises close to the previous nerve. It is short and supplies the posterior belly of diagastric muscle.
THE STYLOHYOID BRANCH
It may arise with the diagastric branch. It is long and supplies the stylohyoid muscle.
TERMINAL BRANCHES WITH IN THE PAROTID GLAND
THE TEMPORAL BRANCH
It emerges from the upper border of the gland and supplies
The anterior and superior auricular muscles
The frontal belly of occipitofrontalis
The orbicularis occuli
The corrugator supercilli
THE ZYGOMATIC BRANCH
It emerges from the anterior border of the gland and supplies the orbicularis occuli
THE BUCCAL BRANCH
It emerges from the anterior border of gland below the parotid duct and supplies the buccinator muscle and muscles of upper lip and nostril.
THE MANDIBULAR BRANCH
It emerges from the anterior border of the gland and supplies the muscles of lower lip.
THE CERVICAL BRANCH
It emerges from the lower border of the gland and passes forward in the neck below the mandible to supply depressor anguli oris muscle.
The facial nerve is the nerve of second arch and supplies all muscles of facial expression. It does not supply skin but its branches communicate with branches of trigeminal nerve.
Routinely only the motor function of the 7th nerve is tested.
· When 7th nerve is paralyzed, the patient may complain of inability to close the eyelid, collection of food in the mouth and dribbling of saliva on the affected side of the mouth and deviation of the angle of the mouth towards the opposite side.
On inspection, palpebral fissure may be wide and nasolabial fold may be flattened on theparalyzed side.
· Ask the patient to frown or wrinkle the forehead.
There would be no wrinkling on the affected side.
· Ask the patient to close the eyes; the affected side will remain open and there will be brisk upward rolling of the eye ball (Bell’s phenomenon). To test the power of orbicularis occuli ask the patient to close the eyes as strongly as possible while you try to open the upper eyelids. The affected side will be weak.
· Ask the patient to inflate the cheek and tap on both sides with finger. The weak side will be deflated easily.
· Ask the patient to show the teeth. The angle of mouth will be deviated towards the healthy side.
· The patient cannot whistle as air escapes from the paralyzed side.
· The patient will complain of unusually loud sounds on paralyzed if nerve to Stapedius is involved.
Test taste of the anterior two third of the tongue by following technique.
· Get solutions of four common tastes- sweet, salt, sour and bitter.
· Instruct the patient to identify the taste, either by writing or raising fingers, e.g. one finger if taste is sweet, two fingers if salty and so on.
· Ask the patient to protrude the tongue. Hold it with a gauze, dry it and test each side separately.
· Put a drop of each solution one by one and ask for response.
· Test bitter at the end.
Lacrimation and salivation can be tested by various tests but it is not done routinely.
The facial nerve is the most commonly affected cranial nerve by lesion of both upper motor neuron and lower motor neuron.
UPPER MOTOR NEURON LESION
Manifestations are on the opposite side. Upper half of the face (wrinkling of the forehead, closure of the eyelid) is less severely affected because the part of the facial nerve nucleus which supplies muscles of the upper half of the face is connected with both cerebral hemispheres; the part of the facial nerve nucleus which supplies muscles of lower half of the face is connected only with the contra lateral cerebral hemispheres. Smiling and other emotional movements are usually preserved in UMN lesion because there is a separate path for these movements.
LOWER MOTOR NEURON LESION
Whole of the ipsilateral half of the face is affected. Bell’s palsy is the most common cause of isolated lower motor neuron facial palsy. Etiology is unknown. The lesion is in the facial canal.
As facial nerve has a long route and gives off branches at various sites, the site of lesion can be localized with considerable precision.
· If the lesion is after the nerve exits from the skull, there is only weakness of the facial muscles.
· If the lesion is in the facial canal, between the chorda tympani and branch to Stapedius, in addition to motor weakness, there is loss of taste as well.
· If the lesion is between the branch to Stapedius and internal auditory meatus, there is hyperacusis on the affected side, in addition to motor weakness and loss of taste.
· Geniculate ganglion can be affected by herpes zoster(Ramsay Hunt syndrome). In addition to other features of facial palsy, there are vesicles in that part of external auditory meatus which gets sensory supply from the facial nerve.
· If the lesion is in the internal auditory meatus, in addition to the features of facial nerve palsy, 8th nerve is also paralyzed.
· If the lesion is in the cerebello-pontine angle, there are signs of cerebellar dysfunction and 5th, 6th, 7th, and 8th nerves are also involved.
· In pontine lesion, along with the facial nerve, the 6th nerve is also paralyzed and there is upper motor neuron hemiplagia on the opposite side.