antomy of facial nerve and its clinical importance

1. FACIAL NERVE
Dr Shermil sayd

2. Introduction
 Seventh cranial nerve
 Nerve of the second branchial arch
 Motor nerve supply of the face

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

20. Stylohyoid branch
 Arise with the digastric branch
 Its long and supplies the stylohyoid muscle

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

22. Zygomatic branch
 Runs across the zygomatic bone and supply the
orbicularis occuli

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

30. Clinical anatomy

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

37. VII disorders
Bilateral nerve paralysis
1. Melkersson syndrome
2. Möbius syndrome & Congenital facial paresis
3. Guillain barre disease
4. Leprosy
5. HIV infection
6. Myasthenia gravis

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.

42. Thank You