Facial Nerve
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Transcript of Facial Nerve
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FACIAL NERVE
Introduction
Functional components
Branches
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Introduction to Facial Nerve
• seventh (VII) of twelve paired cranial nerves.• emerges from the brainstem between the pons and
the medulla• controls the muscles of facial expression, and functions in the
conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity.
• also supplies pre-ganglionic parasympathetic fibers to several head and neck ganglia.
• nerve of the second branchial arch
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FUNCTIONAL COMPONENTS OF FACIAL NERVE
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Brief overview of cranial nerve functional components
• The 12 cranial nerves participate in a total of seven neural functions. Each of these seven functions is designated by a three letter acronym.
• The first letter is either G (General) or S (Special).– General refers to primitive and/or external structures of the body.– Special refers to senses unique to the head (taste, olfaction, hearing, vision, and
balance) and to muscles of branchial arch derivatives.• The second letter is either S (Somatic) or V (Visceral).
– Somatic refers to non-visceral structures including skin, muscles, tendons, joints, retina (vision), basilar membrane (hearing), and utricle/saccula (balance).
– Visceral refers to organs of the body cavity, smooth muscle, vessels, and glands.• The third letter is either A (Afferent) or E (Efferent).
– Afferent refers to flow of neural information toward the brain (sensation)– Efferent refers to flow of neural information toward the periphery (motor).
• Knowledge of the functional components and the deficits that follow damage to each provides the basis of the thorough neurological exam.
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The Seven Functional Components• GSA – General Somatic Afferent
– Touch, temperature, and pain from non-visceral structures• GSE – General Somatic Efferent
– Motor to skeletal muscle• GVA – General Visceral Afferent
– Touch (distention), temperature, and pain from the viscera• GVE – General Visceral Efferent
– Motor to viscera, smooth muscle, and glands• SSA – Special Somatic Afferent
– Vision, hearing, and balance• SSE – Doesn’t exist• SVA – Special Visceral Afferent
– Taste and olfaction• SVE – Special Visceral Efferent
– Motor to muscles derived from the branchial arches
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Facial nerve nuclei
1. Special visceral or branchial efferent: to muscles of facial expression and elevation of hyoid bone.
2. General visceral efferent or parasympathetic: secretomotor to the submandibular and sublingual salivary glands, the lacrimal glands and glans of nose, the palate and the pharynx.
3. General visceral afferent component: carries afferent impulses from the above mentioned glands.
4. Special visceral afferent : carries taste sensation from the palate and from the anterior two thirds of the tongue except the vallate papillae.
5. General somatic afferent: Sensory from somatic touch, temperature, and pain.
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Origin and course• The facial nerve consists of a motor and a sensory part,
the latter being frequently described under the name of the nervus intermedius (pars intermedii of Wrisberg).
• The two parts emerge at the lateral part of the lower border of the pons in the recess between the olive and the inferior peduncle, just medial to the eighth cranial nerve.
• The two nerves, with the motor nerve being medial run laterally and forwards, with the eighth nerve to reach the internal acoustic meatus.
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Overview of Facial Nerve anatomy in the skull
Lacerate foramen
Facial canal
Internal AcousticMeatus
StylomastoidForamen
Hiatus of canal of greater superficial petrosal nerve
Pterygoid canalGreater superficialPetrosal nerve (GSPN)
Petrotympanicfissure
Greater andlesser palatinecanals
Chorda tympani nerve
Facial nerve
Facial nerve
PosteriorCranialFossa (PCF)
Inferior Orbital Fissure
The facial nerve exits the posterior cranial fossa (PCF) at the internal acoustic meatus.
Click here to start Animation
Posteriorauricular N.
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• In the meatusThe motor nerve lies in a groove
on the eighth nerve, with the sensory nerve intervening
Here, the seventh and the eighth nerve are accompanied by the labyrinthine vessels
At the bottom or fundus of the meatus, the two roots, sensory and motor, fuse to form a single trunk, which lies in the petrous temporal bone.
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• Within the facial canal:The course can be divided into three parts by two
bendsParts:The first part is directed laterally above the
vestibule.The second part runs backwards in relation to the
medial wall of the middle ear, above the promontory.
The third part is directed vertically downwards behind the promontory.
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Course of facial nerve in facial canal(intracranial)
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• Bends:• The first bend at the junction of the first and
second parts is sharp. It lies over the anterosuperior part of the promontory, and is also called the genu, and so the name geniculate ganglion of the nerve as it lies on the genu.
• The second bend is gradual, and lies between the promontory and the aditus to the mastoid antrum.
• The facial nerve leaves the skull by passing through the stylomastoid foramen.
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• Extracranial courseThe facial nerve crosses the lateral side of the base of the
styloid process
Enters the posteromedial surface of the parotid gland
Runs forwards through the gland crossing the retromandibular vein and the external carotid artery
Behind the neck of the mandible, it divides into its five terminal branches which emerge along the anterior border of the parotid gland
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Overview of Facial Nerve anatomy in the skull
Lacerate foramen
Facial canal
Internal AcousticMeatus
StylomastoidForamen
Hiatus of canal of greater superficial petrosal nerve
Pterygoid canalGreater superficialPetrosal nerve (GSPN)
Petrotympanicfissure
Greater andlesser palatinecanals
Chorda tympani
Facial nerve
Facial nerve
PosteriorCranialFossa
Inferior Orbital Fissure
Click here to start Animation
The descending portion of the facial nerve exits the facial canal at the stylomastoid foramen and continues into the parotid region
ParotidregionPosterior
auricular N.
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Nuclei of the Facial Nerve
• Motor nucleus of facial nerve• Superior salivatory nucleus• Nucleus of tractus solitarius• Lacrimatory nucleus
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Facial motor nucleus• Situated in the caudal portion of the ventrolateral pontine tegmentum.• Its axons take an unusual course, traveling dorsally and looping around the abducens
nucleus, then traveling ventrally to exit the ventral pons medial to the spinal trigeminal nucleus. These axons form the motor component of the facial nerve, with parasympathetic and sensory components forming the nervus intermedius.
• The part of the nucleus that supplies muscles of upper part of face receives corticonuclear fibres from the motor cortex of both the right and left sides. In contrast, the part of the nucleus that supplies muscles of the lower part of the face receive corticonuclear fibres only from the opposite cerebral hemisphere.
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Superior salivatory nucleus• Lies in the lower pons• Sends fibres through the facial nerve and its chorda
tympani branch to the submandibular ganglion for supply of the submandibular and the sublingual salivary glands.
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Nucleus of tractus solitarius• The nucleus of the solitary
tract, or NTS (Latin: nucleus tractus solitarii), is located along the length of the medulla oblongata (with a small portion in the lower pons).
• Receive visceral sensation and taste from the facial (VII),glossopharyngeal (IX) and vagus (X) cranial nerves.
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Lacrimatory nucleus• Lies near salivatory nucleus(in the lower pons)• Gives off fibres that pass through the facial
nerve and its branch, the greater petrosal nerve to relay in the pterygopalatine ganglion and supply the lacrimal, nasal and palatal glands.
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Facial Nerve Branches and Supply
1.Within the facial
canal
•Greater petrosal nerve•The nerve to stapedius•The chorda tympani
2.At its exit from the
stylomastoid foramen
•Posterior auricular•Digastric •Stylohyoid
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3.Terminal branches within
the parotid gland
•Temporal•Zygomatic •Buccal•Marginal mandibular•Cervical
4.Communicating branches with
adjacent cranial and spinal nerves
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The greater superficial petrosal nerve
• Arises from the geniculate ganglion, and consists chiefly of sensory branches which are distributed to the mucous membrane of the soft palate; but it probably contains a few motor fibers which form the motor root of the sphenopalatine ganglion.
• It passes forward through the hiatus of the facial canal, and runs in a sulcus on the anterior surface of the petrous portion of the temporal bone beneath the semilunar ganglion, to the foramen lacerum and in the foramen is joined by the deep petrosal, from the sympathetic plexus on the internal carotid artery, to form the nerve of the pterygoid canal which passes forward through the pterygoid canal and ends in the sphenopalatine ganglion.
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Overview of Facial Nerve anatomy in the skull
Lacerate foramen
Internal AcousticMeatus
StylomastoidForamen
Hiatus of canal of greater superficial petrosal nerve
Pterygoid canalGreater superficialPetrosal nerve (GSPN)
Petrotympanicfissure
Greater andlesser palatinecanals
Chorda tympani
Facial nerve
Facial nerve
PosteriorCranialFossa
Inferior Orbital Fissure
Click here to start Animation
The first branch of the facial nerve, the greater superficial petrosal nerve (GSPN) branches from the geniculate ganglion within the genu of the facial canal and enters the middle cranial fossa (MCF) by way of the hiatus of the canal for the GSPN.
Geniculate ganglion
Facial canal
MCF
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Action of superficial greater petrosal nerve:1. Sensation of light touch, temperature, and
pain from the soft palate.2. Taste from the hard and soft palate
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Sensation of light touch, temperature, and pain from the soft palate.
soft palate
Light touch, temperature,and pain fromthe soft palate
Click here for animation
GVA
Light touch sensation
Temperature sensation
Pain sensation
GSPN
Facial nerve
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Soft palate
Taste from the hard and soft palate
Click here for animation
Hard palate
CoSweetened coffee
SVA
GSPN branches fromthe facial nerve at thegeniculate ganglion within the genu of thefacial canal
Taste from the hard and soft palate
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The nerve to stapedius• Arises opposite the pyramid of the middle ear,
and supplies the stapedius muscle• Action :the muscle dampens excessive
vibrations of the stapes caused by high-pitched sounds.
• In paralysis of the muscle, even normal sounds appear too loud and is known as hyper acusis.
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Lacerate foramen
Facial canal
Internal AcousticMeatus
StylomastoidForamen
Hiatus of canal of greater superficial petrosal nerve
Pterygoid canalGreater superficialPetrosal nerve (GSPN)
Greater andlesser palatinecanals
Chorda tympani
Facial nerve
Facial nerve
PosteriorCranialFossa
Inferior Orbital Fissure
Click here to start Animation
The second branch of the facial nerve, the stapedial nerve, branches from the descending portion of the facial nerve and enters the middle ear.
Stapedial N. Petrotympanicfissure
Posteriorauricular N.
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\Stapedius muscle dampens movement of the ossicles protecting the inner ear from damage from loud noises
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The Stapedius muscle dampens movement of the ossicles
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The chorda tympani nerveArises in the vertical part of the facial canal about 6 mm above the stylomastoid foramen
It runs upwards and forwards in a bony canal
Enters the middle ear and runs forwards in close relation to the tympanic membrane
Leaves the middle ear by passing through the petrotympanic fissure
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Then passes medial to the spine of the sphenoid and enters the infra-temporal fossa
Here, it joins the lingual nerve through which it is distributed
It carries:1. Preganglionic fibres to the
submandibular ganglion for the supply of the submandibular and sublingual salivary glands
2. Taste fibres from the anterior two-thirds of the tongue except the circumvallate papillae
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Lacerate foramen
Facial canal
Internal AcousticMeatus
StylomastoidForamen
Hiatus of canal of greater superficial petrosal nerve
Pterygoid canalGreater superficialPetrosal nerve (GSPN)
Petrotympanicfissure
Greater andlesser palatinecanals
Chorda tympani N.
Facial nerve
Facial nerve
PosteriorCranialFossa
Inferior Orbital Fissure
Click here to start Animation
The third branch of the facial nerve, the chorda tympani nerve, branches from the descending portion of the facial nerve and enters the middle ear. Within the middle ear the chorda tympani nerve crosses the medial surface of the tympanic membrane. It then passes through the petrotympanic fissure to enter the infratemporal fossa.
Infratemporalfossa
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The GVE component of the facial nerve transmits preganglionic fibers to the submandibular ganglion via the chorda tympani nerve. From the submandibular ganglion postganglionic fibers innervate the submandibular and sublingual glands, causing salivation.
Superior salivary nucleus
Click here to start Animation
Submandibularganglion
Submandibulargland
Sublingulalgland
GVE
Chordatympani
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SVA component provides taste to the anterior 2/3 of the tongue via the chorda tympani nerve.
Click here for animation
Taste from the anterior 2/3 of the tongue
SVA
Chorda tympani
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The posterior auricular nerve
• Arises just below the stylomastoid foramen• Ascends between the mastoid process and the
external acoustic meatus• Supplies :– Auricularis posterior– Occipitalis– Intrinsic muscles of back of auricle
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The Posterior Auricular nerve innervates the posterior auricular muscle, pulling the pinna posteriorly.
Click here to start Animation
SVE component of posterior auricular nerve
Posterior auricularmuscle pulls the pinna posteriorly
SVE
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GSA component provides touch, temperature, and pain sensation from the external acoustic meatus.
Click here to start animation
Cotton swab
Touch, temperature, and pain sensation from part of the external acoustic meatus.
GSA
Posteriorauricularnerve
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Digastric branch• Arises close to the posterior auricular branch• Short• Supplies the posterior belly of digastric muscle
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Through the stylomastoidforamen
4. The Posterior belly of digastric muscle elevates the hyoid bone
Click here to start Animation
Posterior belly of digastric branch of facial nerveinnervates posterior belly of digastric muscle.
Posterior belly of digastric muscle elevates the hyoid bone
SVEThrough the internalacoustic meatus
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Stylohyoid nerve
• Arises with the digastric branch• Long and supplies the stylohyoid muscle
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Stylohyoid muscle elevates the hyoid bone.
Through the internalAcoustic meatus
Through the stylomastoidforamen
3. The Stylohyoid muscle elevates the hyoid bone
Click here to start Animation
Stylohyoid branch of facial nerveinnervates stylohyoid muscle
SVE
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Temporal branch• Crosses the zygomatic arch andsupply– Auricularis anterior– Auricularis posterior– Intrinsic muscles on the lateral side of the ear– Frontalis– Orbicularis oculi– Corrugator supercilli
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Zygomatic branch
• Runs across the zygomatic bone and supplies the orbicularis oculi
• Together with temporal branch of ipsilateral side acts to close the eyelid
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The temporal and zygomatic branches of the facial nerve provide SVE nerve fibers that innervate the ipsilateral orbicularis oculi, the muscle responsible for closing the eyelid.
Click here to start Animation
Temporal branch
Zygomatic branch
SVEContraction of orbicularisoculi causes the eyelid to close
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Buccal branch• Two in number• The upper buccal branch runs above the parotid
duct and the lower buccal branch below the duct• They supply the muscles in the vicinity esp.
buccinator
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The buccal branch of the facial nerve innervates the buccinator muscle, the muscle responsible for holding the cheek against the teeth, thus positioning food for chewing.
Click here to start Animation
Buccal branch offacial nerve innervatesBuccinator muscle.
SVE Contraction of the buccinator musclecauses tensing of the cheek whichhelps position food within the occusal planefor chewing
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The zygomatic and buccal branches of the facial nerve innervate the ipsilateral zygomaticus major muscle, the main muscle responsible for smiling.
Click here to start Animation
Zygomatic branch
SVE
Zygomaticus major muscle
Contraction of the zygomaticus major musclecauses smiling
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Marginal mandibular branch
• Runs below the angle of mandible deep to platysma
• Crosses the body of mandible and supplies muscles of lower lip and chin
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The mandibular and buccal branches of the facial nerve innervate the ipsilateral depressor angularis oris muscle, a muscle responsible for frowning.
Click here to start Animation
Mandibular branch
SVE
Depressorangularis oris
Contraction of thedepressor angularis orismuscle causes frowning
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• Mandibular Branch (additional)• Familiarity with the location of the marginal
mandibular nerve is essential when operating in the lower face (Fig. 8.7). If the marginal mandibular nerve is injured during surgery, the resulting paralysis of the muscles that depress the corner of the mouth is quite deforming. Dingman and Grabb (1962) noted in a large cadaver study that, posterior to the facial artery, the marginal mandibular nerve passed above the inferior border of the mandible in 81% of dissections..
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• Anterior to the facial artery, all the mandibular nerve branches that innervated the mouth depressors passed above the lower border of the mandible. The only nerve branches that passed below the mandible anterior to the facial artery innervated the platysma and were therefore not of major surgical concern. The nerve was superficial to the posterior facial vein in 98% of the cases and superficial to the anterior facial vein in 100% of the cases.
• The same study showed that the mandibular nerve may have one (21%), two (67%), three (9%), or four (3%) major branches. In 5% of the cases, there was anastomosis between the buccal and mandibular rami
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• Baker and Conley (1979) write that, in their clinical experience, the mandibular branch of the facial nerve is usually 1 to 2 cm below the lower border of the mandible and can be as much as 3 or 4 cm below it. The mandibular branch is deep to the platysma muscle and therefore fairly well protected throughout its course along the mandible (Fig. 8.8). As it approaches the mouth, it becomes more superficial and enters the undersurface of the depressor muscles (Fig. 8.9). Liebman et al. (1988) performed serial sections of cadavers and described the depth of the marginal nerve around the mouth (Fig. 8.7).
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Cervical branch
• Emerges from the apex of the parotid gland • Runs downwards and forwards in the neck to
supply platysma
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E. The cervical branch of the facial nerve innervates the platysma muscle, a muscle partly responsible for depressing the mandible.
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Platysma muscle
Cervical branch offacial nerve innervatesPlatysma muscle.
Contraction of platysmaMuscle results in depressionof mandible.
SVE
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Stapedius muscle dampens movement of ossicles.
Summary of SVE
Facial canal
Internal AcousticMeatus
StylomastoidForamen
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Temporal-orbicularis oculi closes eyelids.Zygomatic-zygomaticus majorpartly responsible for smiling.Buccal-buccinator tenses cheekMandibular-depressor angularis oris responsible for frowning.Cervical- platysma helps lower mandible and tightens skin of neck.
Posterior auricularmuscle responsible forposterior displacementof pinna.
Facial nerve
Facial nerve
Posterior belly of digastricelevates hyoid bone.
Stylohyoid muscleelevates hyoid bone.
Posteriorauricular N.
Facialnucleus
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Communicating branches• For effective coordination between the
movements of the muscles of the first, second and third branchial arches, the motor nerves of the three arches communicate with each other
• Facial nerve also communicates with the sensory nerves distributed over its minor territory
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Ganglions associated with facial nerve1. The geniculate ganglion:
-located on the first bend of the facial nerve, in relation to the medial wall of middle ear in the facial canal -a sensory ganglion -receives fibers from the motor, sensory,
and parasympathetic components of the facial nerve and sends fibers that will innervate the lacrimal glands, submandibular glands, sublingual glands, tongue, palate, pharynx, external auditory meatus, stapedius, posterior belly of the digastric muscle, stylohyoid muscle, and muscles of facial expression.
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Geniculate ganglion
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• Contains special sensory neuronal cell bodies for taste, from fibers coming up from the tongue through the chorda tympani and from fibres coming up from the roof of the palate through the greater petrosal nerve.
• Sensory and parasympathetic inputs are carried into the geniculate ganglion via the nervus intermedius.
• Motor fibers are carried via the facial nerve proper.
• The greater petrosal nerve, which carries sensory fibers as well as preganglionic parasympathetic fibers, emerges from the anterior aspect of the ganglion.
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2. The submandibular ganglion: – (Submaxillary ganglion in older texts) - part of the human autonomic
nervous system.– One of four parasympathetic ganglia of the head and neck. (others are the
otic ganglion, pterygopalatine ganglion, and ciliary ganglion).– Function: responsible for innervation of two salivary glands:
the submandibular gland and sublingual gland.
•small and fusiform in shape.•situated above the deep portion of the submandibular gland, on the hyoglossus muscle, near the posterior border of the mylohyoid muscle. •the ganglion 'hangs' by two nerve filaments from the lower border of the lingual nerve•suspended from the lingual nerve by two filaments, one anterior and one posterior. Through the posterior of these it receives a branch from the chorda tympani nerve which runs in the sheath of the lingual nerve.
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Clinical aspects of Facial Nerve
• Supra nuclear facial paralysis• Bell’s pasly• Melkerson Rosenthal’s syndrome• Ramsay Hunt syndrome