The facial nerve has three nuclei - the main motor nucleus in the pons, parasympathetic nuclei posterolateral to the main motor nucleus, and the sensory nucleus in the upper part of the nucleus of the tractus solitarius. It arises from the brainstem and has an intricate intracranial and extracranial course through the skull and face. It is responsible for motor innervation of facial muscles, special sensory innervation of the anterior two-thirds of the tongue, and parasympathetic innervation via its branches. Facial nerve palsy can result from lesions at different levels and have varying effects depending on the location of the lesion.

1. FACIAL NERVE
Embryology, Internuclear connections, Intracranial and
extracranial course, anatomy and applied anatomy.
Presented By- DR. ANUMITA DEKA
Pg Student, Department of Oral Medicine and Radiology,
K.D Dental College and Hospital, Mathura

2. Introduction:
The facial nerve is one of a group of nerves called the cranial nerves,
twelve pairs of nerves that, with the exception of the spinal
accessory nerve, originate in the brain and contribute to the
peripheral nervous system. They are referred to as “ cranial” because
they arise from the brain and upper spinal cord and supply
structures of the head and neck.
The 12 paired cranial nerves include:
* the olfactory nerve
* the optic nerve
* the occulomotor nerve
* the trochlear nerve
* the trigeminal nerve
* the abducens nerve
* the facial nerve
* the vestibulocochlear nerve
* the glossopharyngeal nerve
* the vagus nerve
* the accessory nerve
* the hypoglossal nerve

3. Organization of the cranial nerves:
The olfactory, optic and vestibulocochlear nerves are entirely
sensory. The oculomotor, trochlear, abducent, accessory and
hypoglossal nerves are entirely motor. The trigeminal, facial,
glossopharyngeal and vagus nerves are both sensory and
motor nerves.
The cranial nerves have central motor and/ or sensory nuclei
within the brain and peripheral nerve fibres that emerge
from the brain and exit from the skull to reach their effector
or sensory organs.
The functions of the cranial nerves are summarized shortly
as follows:

5. The facial nerve
The facial nerve ( also known as the VII cranial nerve) is one of the
twelve cranial nerves. It is predominantly a motor nerve. However,
sensory and vegetative ( parasympathetic) functions are also involved
in its complex role. Facial expressions as the result of activity of
craniofacial muscles, contraction of the muscles derived from the
second pharyngeal arch such as stapedius, platysma, stylohyoid and
posterior belly of digastric, and secretory participation through
general visceral efferent fibres ( salivary, lacrimal, nasal and palatal
glands) are some examples that illustrate the physiological importance
of the VII nerve.

6. Facial nerve embryology
*In the 3rd week of intrauterine development appears the facio-
acoustic primordium, this structure originates from the
rhombencephalon and develops in the rostral sense to the otic
placode. The facial nerve becomes the nerve of the second
branchial arch, and for this reason it will supply all the
elements that derive from it; the stapes, the styloid process of
the temporal bone, the stylohyoid ligament, the minor horn
and the upper portion from the body of the hyoid, also to the
muscles of the stapes, stylohyoid, posterior belly of the
digastric, auricular and facial expression.

7. * In the fourth week of embryogenesis the first branch of the
facial nerve appears in the rostral aspect of the embryo. By the
fifth week, the intermediate nerve becomes evident and two
weeks later will be recognized as an independent nerve.
*Towards the seventh week the tympanic cord will be derived
from the first branch of the facial nerve, joining elements of the
first branchial arch and the lingual nerve (branch of the V part).
By the middle of this week, the trunk of the facial nerve, which
is already formed, bifurcates into the temporofacial and
cervicofacial branches. Around the end of this week different
fascicles that originate from these branches are recognized
clearly. The temporal, zygomatic, oral, mandibular and cervical
regions will give origin to the five main (terminal branches) of
the facial nerve.

8. * In the eighth week of pregnancy the cartilaginous capsule
from the previously formed ear vesicle forms a groove around
the facial nerve, the stapedial artery and the stapes muscle.
This groove will become the facial canal. By week 12 all the
muscles of the face are formed, and all are innervated by one of
the branches of the facial nerve, if the innervation is not
present, the affected muscle fibers will sustain an adipose
involution, a finding described in the Moebius syndrome, in
which there is agenesis or destruction of the nuclei of cranial
nerves VI and VII.

9. * In the twenty-first week, the ossification of the facial canal
begins, which will only end when the collateral branches of the
facial nerve are found in their definitive location and when the
artery has been reversed,4 in many cases, the ossification ends
in the early childhood.
*With respect to the trajectory of the facial nerve during
intrauterine life, literature reports that initially the nerve
presents itself as a rectilinear structure. However, by the sixth
week, due to the mesencephalic growth, there is a change of
direction in acute angle, which will become the knee of the
facial nerve.

10. * Towards the fourth month of formation, a second change of
direction appears, secondary to the development of the
tympanic cavity, which originates from the first branchial
pouch; this second tier will be the elbow of the seventh pair.
*Towards the end of pregnancy, the tympanic bone and the
mastoid process are not fully developed, so the petrous portion
of the facial nerve does not exist and will not be formed until
between 2 and 4 years of age.

11. Facial Nerve Nuclei
The facial nerve has three nuclei: (1) the main motor
nucleus,(2) the parasympathetic nuclei, and (3) the sensory
nucleus.
Main Motor Nucleus
The main motor nucleus lies deep in the reticular formation of
the lower part of the pons. The part of the nucleus
that supplies the muscles of the upper part of the face receives
corticonuclear fibers from both cerebral hemispheres. The
part of the nucleus that supplies the muscles of the
lower part of the face receives only corticonuclear
fibers from the opposite cerebral hemisphere.
These pathways explain the voluntary control of facial
muscles. However, another involuntary pathway exists; it is
separate and controls mimetic or emotional changes in
facial expression. This other pathway forms part of the
reticular formation.

12. Parasympathetic Nuclei
Parasympathetic nuclei lie posterolateral to the main motor
nucleus. They are the superior salivatory and lacrimal
nuclei. The superior salivatory nucleus receives afferent fibers
from the hypothalamus through the descending autonomic
pathways. Information concerning taste also is received from
the nucleus of the solitary tract from the mouth cavity.
The lacrimal nucleus receives afferent fibers from the
hypothalamus for emotional responses and from the sensory
nuclei of the trigeminal nerve for reflex lacrimation secondary
to irritation of the cornea or conjunctiva.

13. Sensory Nucleus
The sensory nucleus is the upper part of the nucleus of the
tractus solitarius and lies close to the motor nucleus. Sensations
of taste travel through the peripheral axons of nerve cells
situated in the geniculate ganglion on the seventh cranial nerve.
The central processes of these cells synapse on nerve cells in the
nucleus. Efferent fibers cross the median plane and ascend to
the ventral posterior medial nucleus of the opposite thalamus
and to a number of hypothalamic nuclei. From the thalamus, the
axons of the thalamic cells pass through the internal capsule
and corona radiata to end in the taste area of the cortex in the
lower part of the postcentral gyrus.

15. Course of the Facial Nerve
*The facial nerve consists of a motor and a sensory root. The
fibers of the motor root first travel posteriorly around the
medial side of the abducent nucleus. They then pass around the
nucleus beneath the colliculus facialis in the floor of the fourth
ventricle and, finally pass anteriorly to emerge from the
brainstem.
*The sensory root (nervus intermedius) is formed of
the central processes of the unipolar cells of the geniculate
ganglion. It also contains the efferent preganglionic
parasympathetic fibers from the parasympathetic nuclei.
The two roots of the facial nerve emerge from the anterior
surface of the brain between the pons and the medulla
oblongata.They pass laterally in the posterior cranial fossa
with the vestibulocochlear nerve and enter the internal
acoustic meatus in the petrous part of the temporal bone.

16. At the bottom of the meatus, the nerve enters the facial canal
and runs laterally through the inner ear. On reaching the
medial wall of the tympanic cavity, the nerve expands to form
the sensory geniculate ganglion and turns sharply backward
above the promontory. At the posterior wall of the tympanic
cavity, the facial nerve turns downward on the medial side of
the aditus of the mastoid antrum, descends behind the pyramid,
and emerges from the stylomastoid foramen.

17. The course of the facial nerve is very complex. There are many
branches, which transmit a combination of sensory, motor and
parasympathetic fibers.
Anatomically, the course of the facial nerve can be divided into
two parts:
Intracranial – the course of the nerve through the cranial cavity,
and the cranium itself.
Extracranial – the course of the nerve outside the cranium,
through the face and neck.
Intracranial
The nerve arises in the pons, an area of the brainstem. It begins
as two roots; a large motor root, and a small sensory root (the
part of the facial nerve that arises from the sensory root is
sometimes known as the intermediate nerve).
The two roots travel through the internal acoustic meatus, a 1cm
long opening in the petrous part of the temporal bone. Here,
they are in very close proximity to the inner ear.
Still within the temporal bone, the roots leave the internal
acoustic meatus, and enter into the facial canal. The canal is a
‘Z’ shaped structure.

18. Within the facial canal, three important events occur:
Firstly the two roots fuse to form the facial nerve.
Next, the nerve forms the geniculate ganglion (a ganglion is a
collection of nerve cell bodies).
Lastly, the nerve gives rise to:
Greater petrosal nerve – parasympathetic fibers to mucous glands
and lacrimal gland.
Nerve to stapedius – motor fibers to stapedius muscle of the
middle ear.
Chorda tympani – special sensory fibers to the anterior 2/3 tongue
and parasympathetic fibers to the submandibular and sublingual
glands.
The facial nerve then exits the facial canal (and the cranium) via
the stylomastoid foramen. This is an exit located just posterior to
the styloid process of the temporal bone.

19. Branches of facial nerve

20. Extracranial
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
the stylohyoid muscle.
The main trunk of the nerve, now termed the motor root of the
facial nerve, continues anteriorly and inferiorly into the parotid
gland (note – the facial nerve does not contribute towards the
innervation of the parotid gland, which is innervated by
the glossopharyngeal nerve).

21. Within the parotid gland, the nerve terminates by splitting
into five branches:
*Temporal branch- innervating the frontalis and orbicularis
oris muscles and the muscles in the upper part of the face.
*Zygomatic branch- innervating the middle part of the face.
*Buccal branch- innervating the cheek muscles, including the
buccinator muscle.
*Marginal mandibular branch- innervating muscles of the
lower part of the face.
*Cervical branch- innervating the muscles below the chin
and, among others, the platysma muscle.
These branches are responsible for innervating the muscles
of facial expression.

22. Terminal branches of the facial nerve:

23. Functions:
Motor Functions
Branches of the facial nerve are responsible for innervating many of
the muscles of the head and neck. All these muscles are derivatives of
the second pharyngeal arch.
The first motor branch arises within the facial canal; the nerve to
stapedius. The nerve passes through the pyramidal eminence to supply
the stapedius muscle in the middle ear.
Between the stylomastoid foramen, and the parotid gland, three more
motor branches are given off:
Posterior auricular nerve – Ascends in front of the mastoid process,
and innervates the intrinsic and extrinsic muscles of the outer ear. It
also supplies the occipital part of the occipitofrontalis muscle.
Nerve to the posterior belly of the digastric muscle – Innervates the
posterior belly of the digastric muscle (a suprahyoid muscle of the
neck). It is responsible for raising the hyoid bone.
Nerve to the stylohyoid muscle – Innervates the stylohyoid muscle
(a suprahyoid muscle of the neck). It is responsible for raising the hyoid
bone.

24. Special Sensory Functions
The chorda tympani branch of the facial nerve is
responsible for innervating the anterior 2/3 of the tongue
with the special sense of taste.
The nerve arises in the facial canal, and travels across the
bones of the middle ear, exiting via the petrotympanic
fissure, and entering the infratemporal fossa. Here, the
chorda tympani ‘hitchhikes’ with the lingual nerve. The
parasympathetic fibres of the chorda tympani stay with
the lingual nerve, but the main body of the nerve leaves
to innervate the anterior 2/3 of the tongue.

25. Parasympathetic Functions
The parasympathetic fibres of the facial nerve are carried by
the greater petrosal and chorda tympani branches.
Greater Petrosal Nerve
The greater petrosal nerve arises immediately distal to
the geniculate ganglion within the facial canal. It then moves in
anteromedial direction, exiting the temporal bone into
the middle cranial fossa. From here, its travels across (but not
through) the foramen lacerum, combining with the deep
petrosal nerve to form the nerve of the pterygoid canal.
The nerve of pterygoid canal then passes through the pterygoid
canal (Vidian canal) to enter the pterygopalatine fossa, and
synapses with the pterygopalatine ganglion. Branches from this
ganglion then go on to provide parasympathetic innervation to
the mucous glands of the oral cavity, nose and pharynx, and
the lacrimal gland.

26. Chorda Tympani
The chorda tympani also carries some
parasympathetic fibres. These combine with
the lingual nerve (a branch of the trigeminal nerve)
in the infratemporal fossa and form
the submandibular ganglion. Branches from this
ganglion travel to the submandibular and
sublingual salivary glands.

27. Image demonstrating branches of the
facial nerve:

28. Applied Anatomy of the facial nerve:
Facial paralysis, often unilateral, may be due to:
(1) Supranuclear lesions in the cortico nuclear fibers
from the frontal lobe, variably combined with
numerous other descending fibers converging in the
facial nucleus.
(2) Nuclear or infranuclear lesions involving lower
motor neurons.

29. Supranuclear facial paralysis involving “upper motor
neuron” pathways is usually a part of hemiplegia.
Movements in the lower part of the face are usually
more severely affected, voluntary movements being
weak or absent though emotional expression is little
affected. Electrical reaction of affected muscles are
unaltered. Occasionally supranuclear lesions may
abolish or weaken emotional movements but not
voluntary movements. This dissociation shows that
the supranuclear control of expressive movements is
separate from the corticonuclear path for voluntary
movements.

30. Nuclear or infranuclear lesions vary in their effects
according to the lesion’s site. If the nucleus or facial
pontine fibres are involved, neighboring structures
are inevitably also involved. Facial muscles are
represented in cell groups within the nucleus; their
degree of involvement governs the extent of
paralysis, which is ipsilateral. Lesions due to
adjacent damage include paralysis of the lateral
rectus because of involvement of the abducent
nucleus around which the facial nerve loops.

31. Bilateral facial paralysis are caused by
(1) Bilateral infranuclear lesion’s :
• Acute idiopathic polyneuritis
• Leprosy
• Leukemia
• Syphilitic or meningococcal meningitis
• Double otitis media
• Rheumatic
• Post diphtheritic
• Bell’s Palsy
• Uveoparotid paralysis
(2) Muscle diseases:
• Myasthenia gravis/ myotonic dystrophy
• Facio-scapulo humeral dystrophy
Signs: Flattening of all normal folds, sagging of corners of
mouth, fixed expression less mask like face, no voluntary
movements of facial muscles. White of eye seen when patient
attempts to close them. Patient talks as if he had severe
stomatitis.

32. BELL’S PALSY
Is an acute apparently isolated facial palsy for which no cause
can be found.
Aetiology:
(a) Associated known clinical condition – Diabetes Mellitus,
severe hypertension in last trimester of pregnancy, dental
anesthesia.
(b) Causes – (i) Exposure to cold, oedema and subsequent
compression of the nerve trunk within rigid fallopian canal
causes circulatory disturbance, (ii) other important causes of
acute facial palsy include suppurative otitis media, herpes
zoster, head injury, Guillian-Barre syndrome, sarcoidosis and
multiple sclerosis.

34. Symptoms: sudden following exposure to chill or without any apparent
precipitating cause, maximum paralysis in twenty-four hours. Post
auricular pain is common and many precede paralysis by two days.
There may be spontaneous loss of sense of taste, hyperacusis and
watering of eyes. Sweating is less on affected side.
Signs: Forehead cannot be wrinkled, frowning lost, eyes cannot be
closed. On attempting closure eye ball turns upwards and outwards,
known as Bell’s phenomenon. On showing teeth, the lips do not
separate on affected side. Whistling not possible. Articulation of labial
components difficult. Nasolabial fold flattened out. Angle of affected
side droops with dribbling of saliva. Cheeks puffs out with expiration
because of buccinator paralysis. Food collects between teeth and
paralysed cheek. Fluid runs out while drinking. Base of tongue
lowered.Vesicles within the external auditory meatus and ear drum in
Ramsay Hunt Syndrome. Pain may precede facial weakness. Deafness
may result.
Investigations: Electromyography.
Management: Local heat.
Local treatment of muscles.
Protection of eye

35. REFERENCES:
* Snell- Neuroanatomy- 7th- Edition, Chapter 11 “ The Cranial
Nerve Nuclei and Their Central Connections and Distribution.”
* Anatomy, descriptive and surgical by Henry Gray, H.V. Carter.
* Danilo Alejandro Garcia, “ Facial nerve: embryology and
anatomy of its nucleus.”; Mini Review Article Med Crave; MOJ
Anatomy & Physiology. 2018; 5(3): 164- 166.
* Terence M. Myckatyn, M.D. And Susan E. Mackinnon, M.D. “ A
review of Facial Nerve Anatomy.” Seminars in Plastic Surgery/
Volume 18, Number 1 2004.
* Liam Curry, “ The Facial Nerve ( CN VII).”; August 16, 2020, 66th
Revision.

36. THANK YOU