facial nerve

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FACIAL NERVE

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1. Introduction

2. Embryology & Nuclei of origin

3. Course & Relations

4. Branches of facial nerve

5. Functional components

6. Ganglia associated with facial nerve

7. Blood supply

8. Applied Aspect

CONTENTS 3

4

• 7th cranial nerve

• Mixed nerve

• It emerges from the brain stem between the pons and the medulla.

• Function- Conveys taste sensation from anterior 2/3rd of tongue and oral cavity and also , controls the muscles of facial expression.

• Supplies- preganglionic parasympathetic fibres to several head and neck ganglia

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Sensory root

Motor root

Embryology

The facial nerve is developmentally derived from the hyoid

arch, which is the second branchial arch.

It arises as 2 main divisions- motor and sensory

The motor division of facial nerve is derived from the basal

plate of the embryonic pons

The sensory division originates from the cranial neural

crest

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Facial nerve course, branching pattern, and anatomical

relationships are established during the first 3 months

of prenatal life

The nerve is not fully developed until about 4 years of

age.

The first identifiable Facial Nerve tissue is seen at the

third week of gestation- facioacoustic

primordium or crest

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FACIAL NERVE EMBRYOLOGY: 4TH WEEK

By the end of the 4th

week, the facial and

acoustic portions are

more distinct

The facial portion

extends to placode

The acoustic portion

terminates on otocyst

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FACIAL NERVE EMBRYOLOGY: 5TH WEEK

Early 5th week, the

geniculate

ganglion forms

from distal part of

primordium

It separates into 2 branches: main trunk of facial nerve and chorda tympani

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FACIAL NERVE EMBRYOLOGY: 6TH WEEK

Near the end of the 5th

week, the facial motor nucleus is recognizable

The motor nuclei of VI and VII cranial nerves initially lie in close proximity.

The internal genuforms as metencephalon, it elongates and CN VI nucleus ascends

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FACIAL NERVE EMBRYOLOGY: 7TH WEEK

Early 7th week, geniculate ganglion is well-defined and

facial nerve roots are recognizable

The nervus intermedius arises from the ganglion and

passes to brainstem. Motor root fibers pass mainly

caudal to ganglion

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Proximal branches form in the 6th week, posterior

auricular branch, branch of digastric

Early 8th week temporofacial and cervicofacial divisions

present

Late 8th week, 5 major peripheral subdivisions present

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NUCLEI OF ORIGIN

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FUNCTIONAL

COMPONENT

NUCLEI DISTRIBUTION FUNCTION

GVE Superior salivatory

nucleus

(lies in the pons lateral to

the main motor nucleus

of VII )

Submandibular and

sublingual salivary

glands.

Preganglionic

Secretomotor

SVE Motor nucleus of facial

nerve

(lies in lower part of

pons)

Muscles of facial

expression,

stylohyoid, posterior

belly of digastric,

platysma and

stapedius.

Facial expression

SVA Nucleus of tractus

solitarius (lies in

medullla)

Taste buds in the

anterior 2/3rd of

tongue except

vallate papillae.

Taste sensations

GSA Spinal nucleus of Vth

nerve

Part of skin of

external ear.

Exteroceptive

sensation

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COURSE OF FACIAL

NERVE

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The course of facial nerve is divided by stylomastoid

foramen into

INTRACRANIAL

INTRAPETROUS PARTEXTRACRANIAL PART

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The nerve arises in

the pons in brainstem. It

begins as two roots; a

large motor root, and a

small sensory

root (Nervous

intermedius)

The two roots travel

through the internal

acoustic meatus.

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Within the temporal bone, the

roots leave the internal

acoustic meatus, and enter

into the facial canal (‘Z’

shaped) . The two

roots fuse to form the facial

nerve.

1. The nerve forms

the geniculate ganglion

2. The nerve gives rise to

the greater petrosal

nerve (parasympathetic

fibres to glands), the nerve

to stapedius (motor fibres

to stapedius muscle), and

the chorda

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The facial nerve then exits the facial canal

(and the cranium) via the stylomastoid

foramen, located just posterior to the styloid

process of the temporal bone

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After exiting the skull, the

facial nerve turns

superiorly to run just

anterior to the outer ear.

The first extracranial

branch to arise

is the posterior auricular

nerve. It provides motor

innervation to the some of

the muscles around the

ear.

Immediately distal to this,

motor branches are sent to

the posterior belly of the

digastric muscle and to

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The main trunk of the

nerve (motor root of the facial

nerve), continues anteriorly and

inferiorly into the parotid gland.

Within the parotid gland, the nerve

terminates by splitting into five

branches:

1. Temporal branch

2. Zygomatic branch

3. Buccal branch

4. Marginal mandibular branch

5. Cervical branch

These branches are responsible for

innervating the muscles of facial

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Branches

Branches of communication

Branches of distribution

TE

RM

INA

L B

RA

NC

HE

S

EX

TR

AC

RA

NIA

L

INT

RA

CR

AN

IAL1.Greater

petrosalnerve

2.Nerve to stapedius

3.Chorda tympani

1.Posterior auricular nerve

2.Digastric nerve

3.Stylohyoid nerve

1.Temporal

2.Zygomatic

3.Buccal

4.Marginal mandibular

5.Cervical

BRANCHES OF DISTRIBUTION 23

I- WITHIN THE FACIAL CANAL:

1- Nerve to stapedius: supplies the stapedius muscle.

2- Greater superficial petrosal nerve (GSPN) : arises

from the geniculate ganglion.

3- Chorda tympani nerve:

It arises from the facial nerve 6 mm above the stylomastoid

foramen and runs upwards to perforate the posterior bony

wall of the tympanic cavity.

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It then passes forwards on the medial surface of

the tympanic membrane

It comes out of the tympanic cavity through the

petrotympanic fissure to the infratemporal

fossa where it joins the lingual nerve.

Through the lingual nerve, it supplies both the

submandibular and sublingual salivary glands

by secretomotor fibres and taste fibers from the

anterior 2/3 of the tongue

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II- AT THE EXIT FROM THE STYLOMASTOID

FORAMEN

1- Posterior auricular nerve:

to the auricularis posterior and occipitalis muscle.

2- Digastric branch:

to the posterior belly of digastric muscle

3- Stylohyoid branch:

to the stylohyoid muscle

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III- TERMINAL

BRANCHES

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28

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Elevates upper lip

Smile

Snoring

THE BUCCAL BRANCH SUPPLIES:

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Moves skin

of forehead

Flare nostrils

closes the

mouth, puckers

the lips

chewing

smile

Internal acoustic meatus Vestibulocochlear nerve

Geniculate ganglion A. Greater petrosal nerve

B. Lesser petrosal nerve

C. External petrosal nerve

Facial canal Vagus nerve

Stylomastoid foramen IX & X cranial nerve

Greater auricular nerve

Auriculotemporal nerve

Behind ear Lesser occipital

Face V nerve

Neck Transverse cutaneous nerve

Branches of Communication 31

GANGLIA ASSOCIATED WITH

THE FACIAL NERVE 32

GENICULATE GANGLION

• Derived from Latin GENU = "KNEE“

• L-shaped collection of fibers and sensory neurons of

the facial nerve located in the facial canal of the head.

• Receives fibers from the motor, sensory, and

parasympathetic components of the facial nerve

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Innervates

Lacrimal glands

Submandibular glands

Sublingual glands

Tongue

Palate

Pharynx

External auditory meatus

Stapedius

Posterior belly of the

digastric muscle

Stylohyoid muscle

Muscles of facial

expression.

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SUBMANDIBULAR GANGLION

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 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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PTERYGOPALATINE GANGLION

The Pterygopalatine ganglion

(meckel's ganglion, nasal

ganglion or sphenopalatine

ganglion) - parasympathetic

ganglion found in the

pterygopalatine fossa.

It's largely innervated by

the greater petrosal nerve

(a branch of the facial nerve);

and its axons project to the

lacrimal glands and nasal

mucosa

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FACIAL NERVE BLOOD SUPPLY

The facial nerve gets it’s blood supply from

1. Anterior inferior cerebellar artery – at the

cerebellopontine angle

2. Labyrinthine artery (branch of anterior inferior cerebellar

artery) – within internal acoustic meatus

3. Superficial petrosal artery (branch of middle meningeal

artery) – geniculate ganglion and nearby parts

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4. Stylomastoid artery (branch of posterior

auricular artery) – mastoid segment

5. Posterior auricular artery supplies the facial

nerve at & distal to stylomastoid foramen

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Child Adult

Chorda tympani may exit through

Stylomastoid Foramen

Chorda tympani exit proximal to

Stylomastoid Foramen

Nerve trunk is more anterior and lateral

on exit through Stylomastoid Foramen

Nerve trunk is less anterior and deeper

Nerve more superficial over angle of

mandible

Nerve less superficial over angle of

mandible

AGE CHANGES 39

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DISORDERS OF FACIAL

NERVE

Facial nerve lesions:

1. Supra-nuclear type

2. Nuclear type

3. Peripheral lesions

Injury at internal acoustic meatus

Injury distal to geniculate ganglion

Injury at stylomastoid foramen

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1. SUPRA NUCLEAR TYPE:

Features:

a) Paralysis of lower part of face (opposite

side)

b) Partial paralysis of upper part of face

c) Normal taste and saliva secretion

d) Stapedius not paralysed

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2. NUCLEAR TYPE:

Features:

a) Paralysis of facial muscle (same side)

b) Paralysis of lateral rectus

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3. PERIPHERAL LESION

a) At internal acoustic meatus

Features:

i. Paralysis of secretomotor fibers

ii. Hyper acusis

iii. Loss of corneal reflex

iv. Taste fibers unaffected

v. Facial expression and movements paralysed

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b) Injury distal to geniculate ganglion

Features:

i. Complete motor paralysis (same side)

ii. No hyper acusis

iii. Loss of corneal reflex

iv. Taste fibers affected

v. Facial expression and movements

paralysed.

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c) Injury at stylomastoid foramen

• Condition known as Bell’s Palsy

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1. BIRTH

Forceps delivery

Dystrophia myotonica

Moebius' syndrome (facial diplegia

associated with other cranial nerve deficits)

2. TRAUMA

Basal skull fracture

Facial injuries

Penetrating injury to middle ear

Altitude paralysis (barotrauma)

Scuba diving (barotrauma)

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3. INFECTIONS

External otitis

Otitis media

Mastoiditis

Chicken pox

Herpes zoster (Ramsay Hunt

syndrome)

Encephalitis

Poliomyelitis (type I)

Mumps

Leprosy

Coxsackievirus

Malaria

Syphilis

Scleroma

Tuberculosis

Botulism

Mucormycosis

Lyme disease

4.TOXIC 5.METABOLIC 50

Thalidomide (Miehlke syndrome,

cranial nerves VI, VII with

congenital malformed external

ears and deafness)

Tetanus

Diphtheria

Carbon monoxide

Diabetes mellitus

Hyperthyroidism

Pregnancy

Hypertension

Acute porphyria

6.NEOPLASTIC

7th nerve tumour

Leukaemia

Meningioma

Haemangioblastoma

Sarcoma

Carcinoma (invading or metastatic)

Haemangioma of tympanum

Facial nerve tumour (cylindroma)

Schwannoma

Teratoma

Fibrous dysplasia

von Recklinghausen's disease

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7. IATROGENIC 8. IDIOPATHIC 52

Mandibular block anesthesia

Head and neck surgery

Myasthenia Gravis

Guillain-Barre Syndrome

Sarcoidosis

Familial Bell's Palsy

BELL’S PALSY

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Background of BELL’S PALSY

First described more than a

century ago by Sir Charles Bell

Controversy still surrounds its

etiology and management

Bell palsy is certainly the most

common cause of facial paralysis

worldwide

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DEMOGRAPHICS OF

BELLS PALSY

Race: slightly higher in persons of Japanese descent.

Sex: No difference exists

Age: highest in persons aged 15-45 years.

Bell palsy is less common in those younger than 15 years

and in those older than 60 years.

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Pathophysiology of Bells palsy

Main cause of Bell's palsy is latent herpes viruses

(herpes simplex virus type 1 and herpes zoster virus),

which are reactivated from cranial nerve ganglia

Polymerase chain reaction techniques have isolated

herpes virus DNA from the facial nerve during acute

palsy

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I. Unilateral involvement

II. Inability to smile, close eye or raise eyebrow

III. Whistling impossible

IV. Drooping of corner of the mouth

V. Inability to close eyelid (Bell’s sign)

VI. Inability to wrinkle forehead

VII. Loss of blinking reflex

VIII.Slurred speech

IX. Mask like appearance of face

X. Loss/ alteration of taste

FEATURES OF BELL’S PALSY57

MANAGEMENT OF BELLS PALSY

It focuses on protecting the cornea from drying and

abrasion due to problems with lid closure and the

tearing mechanism.

Lubricating drops should be applied hourly during

the day and a simple eye ointment should be used at

night.

EYE CARE

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Treatment consists of Infra-red radiation on affected

side of the face at 2 ft (60cm) ,followed by interrupted

galvanism on affected side

Treatment was given daily at first few weeks & later

thrice weekly.

All patients are instructed to massage the face daily

70-80% of these patients recover completely, while the

reminder develop various sequelae within one to three

months

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MEDICAL TREATMENT

Corticosteroids :

Prednisolone 1 mg/kg/day 7-10 days

Corticosteroids combine with antiviral drug is better

Acyclovir 400 mg 5 times/day

Famciclovir and valacyclovir 500 mg bid

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SURGICAL

TREATMENT

Facial nerve decompression

Indication:

Completely paralysis

Appropriate time for surgery is 2-3 weeks after paralysis

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FACIAL NERVE PARALYSIS

Most commonly during inferior alveolar nerve block or

infraorbital nerve block

Cause

LA into the capsule of the parotid gland

Prevention

Use of proper technique

Avoid over insertion of needle

Treatment

Transient, self correcting with 3 hours or less.

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63

Gray's Anatomy By Richard Drake, A. Wayne Vogl, Adam W. M.

Mitchell.

A.K. Datta Essentials Of Human Anatomy Head And Neck. 4th

Edition

B D CHAURASIA’S Human Anatomy. Volume 3 Edition 4th

Atlas Of Anatomy Edited By Anne M. Gilroy, Brian R.

Macpherson, Lawrence M. Ross

Monheim’s Local Anaesthesia And Pain Control In Dental

Practice

64REFERENCES

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