3. Surface marking
It is marked by a short horizontal line which
joins the following two points
A point at the middle of the anterior border of the mastoid
process. The stylomastoid foramen lies 2cm deep to this
point
A second point behind the neck of the mandible. Here the
nerve divides into its five branches
4. Functional Components
1. Special visceral or branchial efferent-for muscles responsible
for facial expression and for elevation of the hyoid bone
2. General visceral efferent or parasympathetic- they are
secretomotor to the submandibular and sublingual salivary
glands, lacrimal glands & glands of the nose.
3. General visceral afferent- carries afferent impulses from the
above mentioned glands
4. Special visceral afferent fibres- carry taste sensations from
the anterior two third of the tongue, except from vallate
papillae & from the palate
5. 5. General somatic afferent- probably innervate a part of the skin
of the ear. This nerve doesn’t give any direct branches to the
ear. But may reach it through the communication with the
vagus nerve.
6. Nuclei
The four nuclei are presented in the lower pons
1. motor nucleus or the branchiomotor
2. superior salivary nucleus or parasympathetic
3. lacrimatory nucleus is also parasympathetic
4. nucleus of the tractus solitarius which is gustatory
and receives afferent fibres from the glands
7. Motor nucleus lies deep in the reticular formation of the
lower pons
The part of the nucleus that supplies the muscles of the
upper part of the face receives corticonuclear fibres from
the motor cortex of the both left and right sides.
The part of the nucleus that supplies muscles of the
lower part of the face receive corticonuclear fibres only
from the opposite cerebral hemisphere
8. Course and relations
(intracranial)
Attaches to the brain stem by two roots, motor & sensory
(nervus intermedius)
Attached to the lateral part of the lower border of the pons
just medial to the eighth cranial nerve
Two roots run laterally forward to reach the internal
acoustic meatus
In the meatus, motor root lies in a groove on the 8th
nerve,
with sensory root intervening & accompanied by the
labyrinthine vessels
9. At bottom or fundus of the root , sensory and motor join
to form a single nerve trunk which lies in the petrous
temporal bone
Within the canal the nerve course is divided in 3 parts by
two bends
1. Directed laterally above the vestibule
2. Runs backwards and in relation to the medial wall of the
middle ear, above the promontory
3. Vertically downwards behind the promontory
10. 1st
bend at the junction of 1st
and 2nd
part is sharp, lies over
the anterosuperior part of the promontory, Also called as
the genu.
it is called so because it lies on the genu
2nd
bend is gradual and lies between the promontory and
the aditum to the mastoid antrum
Leaves the skull through the stylomastoid foramen
11. Course and relations
(extracranial)
Facial nerve crosses the lateral side of the base of the
styloid process
It enters the posteromedial surface of the parotid gland,
runs forwards through the gland crossing the
retromandibular vein and the ECA.
Behind the neck of the mandible, it divides into 5 terminal
branches which emerge along the anterior border of the
parotid gland
12. Branches and distribution
Within the facial canal
1. Greater petrosal nerve
2. Nerve to the stapedius
3. Chorda tympani
As it exits from the stylomastoid foramen
1. Posterior auricular
2. Digastric
3. Stylohyoid
13. Terminal branches within the parotid gland
1. Temporal
2. Zygomatic
3. Buccal
4. Marginal Mandibular
5. Cervical
Communicating branches with the adjacent cranial and
spinal nerves
14. Greater petrosal nerve
Carries gustatory and parasympathetic fibres
Arises from the geniculate ganglion of the facial nerve,
enters the middle cranial fossa through the hiatus for the
greater petrosal nerve on the anterior surface of the
petrous temporal bone
It proceeds towards the foramen lacerum
Where it joins the deep petrosal nerve which carries
sympathetic fibres to form the nerve of the pterygoid
canal
15. Nerve to the stapedius
Arises opposite the pyramid of the middle ear, and
supplies the stapedius muscle
Damps excessive vibrations of the stapes caused by high
pitched sounds.
In paralysis, it causes hyperacusis
16. Chorda tympani nerves
Arises in the vertical part of the facial canal about 6mm
above the stylomastoid foramen
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
It then passes medial to the spine of the sphenoid and
enters the infratemporal fossa.
Joins the lingual nerve through which it is distributed
17. Carries
1. Preganglionic secretomotor fibres to the submandibular
ganglion for supply of the submandibular and sublingual
salivary glands
2. Taste fibres from the anterior two thirds of the tongue
18. Posterior auricular nerve
Arises just below the stylomastoid foramen
Ascends between the mastoid process and the external
acoustic meatus and supplies
1. The auricularis posterior
2. The occipitalis
3. The intrinsic muscles on the back of the auricle
19. Digastric branch
Arises close to the previous nerve
It is short and supplies the posterior belly of the digastric
21. Temporal branches
Crosses the zygomatic branch
– auricularis anterior
– Auricularis superior
– Intrinsic muscles on the lateral side of the ear
– Frontalis
– The orbicularis occuli
– Corrugator supercili
23. Buccal branches
Two branches
1. Upper- runs above the parotid duct
2. Lower- runs below the duct
They supply the muscles in the vicinity, i.e. muscles of the
cheek and upper lip
24. Marginal mandibular branch
Runs below the angle of the mandible deep into the
platysma
Crosses the body of the mandible and supplies muscles
of the lower lip and the chin
25. Cervical branch
Emerges from the apex of the parotid gland
Runs downwards and forwards in the neck to supply the
platysma
26. Communicating branches
For effective coordination between the movements of the
muscles of the 1st
, 2nd
and 3rd
branchial arches, the motor
nerves of the 3 arches communicate with each other
Also communicates with the sensory nerves distributed
over its motor territory
27. Ganglia
Three ganglions
1. The geniculate ganglion is situated on the 1st
bend of the
facial nerve, in relation to the medial wall of the middle
ear. A sensory ganglion. Taste fibers present are
peripheral processes of pseudounipolar neurons present
in the geniculate ganglion
2. Submandibular ganglion -parasympathetic ganglion for
relay of secretomotor fibres to the submandibular and
sublingual glands
3. Pterygopalatine ganglion is also a parasympathetic
ganglion
31. Facial nerve paralysis
Facial nerve paralysis is the most common complication
in dental practice
Paralysis of some of its branches occur whenever an
infraorbital block/max. canine infiltration given
Muscle droop is observed when the LA solution is
deposited in the deep lobe of the parotid gland, through
which terminal portions of the facial nerve extends, which
is a transient condition
Duration depends upon the duration of action of the LA
solution injected
32. Patient has unilateral facial muscle paralysis & be unable
to use these muscles
Face appears lopsided
No treatment other than waiting until the action of the
drug resolves
Patient is unable to voluntarily close one eye
Protective lid reflex of one eye is abolished, but the
corneal reflex is normal
33. Bell’s palsy
Facial weakness
Evidence for herpes simplex type 1 infection causing
infranuclear lesions
Paralysis: Progresses to maximal deficit over 3 to 72
hours
Pain (50%): Near mastoid process
Hyperacusis
Facial weakness
Sensory loss is Mild or None
34. Food accumulates between the teeth and cheek
Labial articulation is impaired
35. Supra nuclear lesion
Its usually a part of the hemiplegia
Only the lower part of the opposite side of the face is
paralysed
The upper part with the frontalis and orbicularis occuli
escapes due to its bilateral representation in the cerebral
cortex
36. VII disorders
Unilateral nerve paralysis
– Leprosy
– Lyme disease
– Neoplasm and masses
– Trauma
– Cardiofacial syndrome
38. Parotid gland relation
During the removal of parotid gland, the facial nerve is
preserved by removing the glands in two parts, superficial
and deep separately.
The plane of cleavage is defined by tracing the nerve
from behind, forwards
Mixed parotid tumour is a slowly growing parotid tumour
which doesn’t involve the facial nerve, but when it turns
malignant, it then involve the facial nerve
39. TMJ relation
Temporal branches of the facial nerve is related to the
lateral aspect of the TMJ
This leads to invariable damage to the facial nerve during
surgical correction of TMJ ankylosis
This can mostly avoided by taking strict care during the
preocedure
Indian Journal of Dental Research. 2013 Jul-Aug;
40. Conclusion
Facial nerve is a nerve which is mostly motor in
function, but also plays a small role in taste sensation. Its
motor function is for the muscles of facial expression, which
is important for a good quality of life. So every care should
be taken to preserve these nerves, whatever the case may
be.
41. References
Oral and maxillofacial surgery-Daniel M laskin
Local anesthesia- malamed
Differential diagnosis of oral and maxillofacial lesions-wood goaz
Contemporary oral and maxillofacial surgery-peterson
Human anatomy-chaurasia
Indian Journal of Dental Research. 2013 Jul-Aug;
Melkersson-Rosenthal syndrome and orofacial granulomatosis-
Dermatol Clin. 1996 Apr;14(2):371-9.
Bell palsy in lyme disease-endemic regions of canada: a cautionary
case of occult bilateral peripheral facial nerve palsy due to Lyme
disease-CJEM. 2012 Sep;14(5):321-4.
Clinical spectrum of peripheral facial paralysis in HIV-infected patients
according to HIV status-int J STD AIDS. 2013 Mar 6.