3. INTRODUCTION
(7TH NERVE)
Facial Nerve is a mixed nerve but predominantly motor.
It is referred to as facial nerve as it supplies the muscles
of facial expression.
4. FACIAL NERVE NUCLEI
1. Main motor nucleus (branchiomotor nucleus or facial
nerve nucleus) – present in pons.
2. Superior salivatory nucleus (lacrimatory nucleus) -
present in pons
3. Nucleus of tractus solitarius - special sensory- in the
MO
4. Spinal nucleus of trigeminal nerve - in the MO
5.
6. FUNCTIONAL COMPONENT AND NUCLEI
Special visceral efferent (SVE) fibres : arise from motor nucleus and
supply muscles derived from 2nd pharyngeal arch.
General visceral efferent (GVE) fibres : are preganglionic
parasympathetic fibres which arise from superior salivatory
nucleus. These fibres supply parasympathetic fibres to lacrimal,
submandibular & sublingual gland.
7. Special visceral afferent (SVA) fibres : They carry special
sensations of taste from anterior two-third of the tongue
with the except circumvallate papillae and terminate in
the nucleus of tractus solitarius (gustatory nucleus) in the
brainstem.
General somatic afferent (GSA) fibres : They carry general
sensations from the skin of the auricle and terminate in
the spinal nucleus of the trigeminal nerve.
8. COURSE AND CONNECTIONS
Anatomically, the course of the facial nerve can be
divided into two parts:
Intracranial – the course of the nerve through the cranial
cavity.
Extracranial – the course of the nerve outside the
cranium, through the face and neck.
9.
10. INTRACRANIAL COURSE OF FACIAL NERVE
Arise by 2 roots : large motor root and small sensory root (nervous
intermedius) which originate from ventral surface of
pontomedullary junction.
Run laterally and forward and enter into the internal acoustic
meatus.
Within the meatus, 2 roots connect & form trunk of the facial
nerve.
The facial nerve enters the facial canal in the petrous part of
temporal bone.
Within the canal, facial nerve divides into 3 parts: labyrinthine,
tympanic and mastoid by 2 bends. (The canal is a ‘Z’ shaped)
11.
12.
13. THERE 3 IMPORTANT EVENTS OCCUR:
1st : the two roots fuse to form the facial nerve.
2nd : the nerve passes through the geniculate ganglion (a
ganglion is a collection of nerve cell bodies outside the CNS).
3rd: the nerve gives rise to:
Greater petrosal nerve – parasympathetic fibres to salivary
glands and lacrimal gland.
Nerve to stapedius – supply stapedius muscle of the middle
ear.
Chorda tympani – special sensory fibres to the anterior 2/3
tongue and parasympathetic fibres to the submandibular
and sublingual glands.
The facial nerve comes out of cranial cavity via the
stylomastoid foramen.
14. EXTRACRANIAL COURSE
After exiting the skull through stylomastoid foramen at the
base of skull, it runs anterolaterally to enter the posteromedial
aspect of parotid gland, where within the gland it divides into
five terminal branches.
15.
16. BRANCHES OF FACIAL NERVE
Intracranial branch:
1. Greater petrosal nerve, which is joined by deep petrosal
nerve to form nerve of pterygoid canal. It provides
secretomotor supply to lacrimal, nasal and palatal
glands.
2. Nerve to stapedius.
3. Chorda tympani nerve, which joins lingual nerve. It carry
taste fibres from anterior two-third of the tongue and
provides preganglion fibres to the submandibular
ganglion.
17. Extracranial branch:
1. POSTERIOR AURICULAR NERVE : occipitalis and
posterior auricular muscles.
2. NERVE TO THE POSTERIOR BELLY OF DIGASTRIC : it
supply to the posterior belly of digastric.
3. NERVE TO STYLOHYOID : supplies the stylohyoid
muscle.
4. TERMINAL BRANCHES : (5 branches) temporal,
zygomatic, buccal, mandibular and cervical to the
muscles of facial expression
18.
19.
20. CLINICAL SIGNIFICANCE
LESIONS OF FACIAL NERVE :
These can be supranuclear or infranuclear.
A supranuclear lesion (in hemiplegia) spares the upper
part of the face because Lower part of face receives
corticonuclear fibres from opposite side of cerebral
cortex while upper part of face receives fibres from
both cerebral hemisphere.
In the supranuclear lesion, only lower half of the face on
the opposite side is paralyzed.
All infranuclear lesions require entire of the face on
precisely the same side.
21.
22.
23. INFRANUCLEAR LESIONS
The signs and symptoms of infranuclear lesions differ based
on the site of the lesion:
Site A - At or just above the stylomastoid foramen: It causes
Bell’s palsy which presents as loss of motor functions of all
muscles of facial expression resulting in the deviation of
mouth toward the normal side, inability to shut the mouth
and eye and accumulation of food in the vestibule of mouth
flattening of expression lines.
Site B Above the origin of chorda tympani: All the signs and
symptoms of lesion A (i.e., Bell’s palsy) plus reduced
salivation and reduction of taste sensations in the anterior
two-third of the tongue.
24. Site C Above the origin of nerve to stapedius: All the signs
and symptoms of lesion B plus hyperacusis (i.e.,
increased susceptibility to hearing).
Site D At the geniculate ganglion: All the signs and
symptoms of lesion C plus reduction of lacrimation.
25. RAMSAY HUNT SYNDROME
It takes place because of the participation of geniculate
ganglion in herpes zoster infection. Medically, it presents
with all these signs and symptoms:
Herpetic vesicles on the auricle.
Hyperacusis.
Reduction of lacrimation.
Loss of taste sensations in the anterior two-third of the
tongue.
Whole ipsilateral facial palsy (Bell’s palsy).
26. CROCODILE TEARS SYNDROME
It is a clinical condition characterized by paroxysmal
lacrimation during eating.
It ends in the facial nerve lesion proximal to the
geniculate ganglion because regenerating preganglionic
fibres intended to supply secretomotor Supply to the
submandibular and sublingual salivary glands during
regeneration are misdirected and grow & join with the
preganglionic secretomotor fibres which supply the
lacrimal gland.
