Anatomy of Facial Anatomy of Facial NerveNerve

Presented by Dr. Ketaki Pawar.

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Table of contents

• Introduction• Surface marking• Functional components• Nuclei• Course and relations• Branches and distribution• Ganglia• Clinical anatomy

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Introduction

• Seventh cranial nerve• 2nd only to vagus as the “busiest” cranial nerve of

the human body• Nerve of the second branchial arch• The facial nerve consists of the facial nerve

proper and the intermedius nerve. • Both the facial nerve proper and the intermedius

nerve emerge from the CNS in the cerebellopontine angle at the caudal border of the pons, between the abducens nerve and the vestibulocochlear nerve .

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Surface markings• Marked by a short

horizontal line which joins following two points:

1)A point at the middle of the anterior border of the mastoid process.

2)Behind the neck of the mandible.

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Functional components

1. Special visceral or branchial efferent, to muscles responsible for facial expression, posterior belly of digastric muscle , stylohyoid and stapedius

2. General visceral efferent or parasympathetic:

These fibers are secretomotor to the submandibular and sublingual salivary glands, the lacrimal gland, and glands of the nose, the palate and the pharynx.

3. General visceral afferent : carries afferent impulses from the above mentioned glands. 5

4. Special visceral afferent fibres carry taste sensations from the anterior two thirds of the tongue except from vallate papillae and from the palate.

5. General somatic afferent fibres innervate a part of skin of the ear .

Brachial motor- largest portion

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7Functional components of facial nerve

Nuclei• The fibres of the nerve arise from four nuclei

situated in the lower pons.1.Motor nucleus or brachiomotor : lies deep in

the reticular formation of the lower pons.2.Superior salivatory nucleus or

parasympathetic.3.Lacrimatory nucleus – parasympathetic.4.Nucleus of tractus solitarius – gustatory and

also receives afferent fibres from the glands.

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Supranuclear anatomy• Cortex and internal capsule:Voluntary responses of the facial muscles arises from efferent discharge from motor face areaof the cerebral cortex.• The motor face area is situatedon the pre central and post central gyrus.

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•Discharges from the facial motor area are carried through fascicles of the corticobulbar tract to the internal capsule, then through the upper midbrain to the lower brainstem, where they synapse in the facial nerve nucleus located in pons.•Corticobulbar tracts arising from the cortical representationof the upper face area cross andrecross in reaching the pontinefacial motor nucleusThe tracts to lower face are crossed only once.

Posterior view of the brainstem

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Contents of right internal auditory canal

•Facial nerve emerges from the brainstem with nervus intermedius•The average distance between the point where the nerves exit the brainstem and the place where they enter the internal auditory canal is approximately15.8 mm

Intracranial course and relations

• Facial nerve is attached to the brainstem by two roots : motor and sensory ( nervus intermedius) which are attached to the lateral part of the lower border of pons just medial to eight cranial nerve.

• The motor and sensory root runs laterally and forwards, with the 8th nerve to reach the internal acoustic meatus. In the meatus the motor root lies in a groove on the 8th nerve with the sensory root intervening.

• At the bottom of the meatus , the two roots fuse to form a single trunk which lies in the petrous temporal bone.

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13Intracranial course of facial nerve

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Within the canal, the course of the nerve can be divided into three parts by two bends:

1.First part is directed laterally above the vestibule.2.Second part runs backwards in relation to the medial wall of the middle ear, above the promontory.3.Third part is directed vertically downwards behind the promontory.

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Intracranial course: facial nerve exits theCranium at the stylomastoid foramen

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• The first bend at the junction of first and second part is sharp and it is called as genu.

• The second bend is gradual and lies between the promontory and the aditus to the mastoid antrum.

• Facial nerve leaves the skull by passing through the stylomastoid foramen.

Extracranial course

• The 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 external carotid artery.

• Behind the neck of the mandible it divides into its five terminal branches which emerge along the anterior border of parotid gland

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Branches and distribution

A. Within the facial canal: 1. Greater petrosal nerve2. The nerve to the stapedius3. Chorda tympani

B. At its exit from the stylomastoid foramen:1. The posterior auricular 2. Digastric3. Stylohyoid

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C. Terminal branches within the parotid gland:1.Temporal 2.Zygomatic3.Buccal4.Marginal mandibular5.Cervical

D. Communicating brancheswith adjacent cranial and Spinal nerves.

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Greater Petrosal nerve• Leaves at the genu• pre ganglionic parasympathetic fibers

pterygopalatine ganglion lacrimal gland• Leaves the facial canal through the hiatus, runs forwards,

downward and inward in a furrow on the anterior surface of the pyramid of the temporal bone.

• Leaves the cranial cavity through foramen lacerum after joining the deeo petrosal nerve from the sympathetic plexus of the internal carotid artery

• Sup and deep petrosal nerves form the pterygoid or the vidian nerve pterygopalatine ganglion

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Nerve to stapedius muscle

• Arises opp. to the pyramid of the middle ear• Supplies the stapedius muscle• Stapedius muscle – dampening of excessive

vibrations of the stapes• In paralysis- hyperacusis

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Chorda tympani

• Arises 6 mm above stylomastoid foramen• Contains taste fibers and preganglionic

parasympathetic secretory fibers• Enters tympanic cavity posterior wall in close

relation to tympanic membrane Leaves the middle ear by passing though petrotympanic fissure Enters infratemporal fossa joins lingual nerve

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Posterior auricular

• Turns backwards and upwards between the mastoid process and the auricle

• Supplies posterior auricular and occipital muscles

Nerve to stylohyoid• Supplies stylohyoid muscle Digastric• Supplies posterior belly of digastric

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Terminal branches

• At the stylomastoid foramen, the main trunk enters the substance of the parotid gland.

• First separation into upper and lower division usually occurs behind the mandible.

• The upper division- temporal, zygomatic and upper buccal

• The lower division- lower buccal, mandibular and cervical

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Temporal

• Emerge from the parotid gland at its upper pole slightly in front of the superficial temporal artery

• Anterior temporal : frontalis, superior part of orbicularis oculi, corrugator supercilii, procerus

• Posterior temporal : anterior and superior auricular muscles

Zygomatic

• Leave the parotid gland on its anterosuperior border

• Crosses the body of zygomatic bone• Supply inferior part of orbicularis oculi

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Buccal• Emerge at the anterior border of parotid• Upper buccal: muscles of upper lip and the

muscles of the nose• Lower buccal : buccinator and risorius• Orbicularis oris

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Marginal mandibular

• Runs parallel to lower border of the mandible• Cross facial vein and facial artery• Supplies muscles of lower lip (depressor anguli

oris and depressor labii inferioris) and mental muscles

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Cervical

• Leaves parotid gland at or slightly above its inferior pole

• Runs downward and anteriorly • Supplies platysma

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Communicating branches

• Facial nerve branches exchange fibers with sensory cutaneous branches of the trigeminal nerve.

• Connections between facial and trigeminal branches results in formation of small mixed terminal nerves, which carry motor and sensory fibers to a limited area of the face

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Terminal motor branches of facial nerve

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Most important of these connections are:

• a branch of the auriculotemporal nerve joins the upper branch of the facial nerve•The upper buccal branches of the facial nerve join branches of the infratemporal nerve in the canine fossa•The cervical branch exchanges fibers with the transverse colli nerve of the cervical plexus.

Ganglia 1. The geniculate ganglion is located on the first bend of

the facial nerve in relation to the medial wall of the middle ear. It is a sensory ganglion. The taste fibres present in the nerve are peripheral processes of pseudounipolar neurons present in the geniculate ganglion.

2. The submandibular ganglion is a parasympathetic ganglion for relay of secretomotor fibre to the submandibular and sublingual glands.

3. The pterygopalatine ganglion is also a parasympathetic ganglion. Secretomotor fibres present for the lacrimal gland relay in this ganglion.

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Vascular Supply

• Proximal and middle portions of the nerve via the anterior inferior cerebellar artery and the internal auditory artery respectively

• Further supply of middle portion of the nerve comes from the petrosal artery via the middle meningeal artery of the external carotid.

• Distal segment – by stylomastoid artery, also a branch of external carotid artery

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References

• B.D. Chaurasia’s Human Anatomy- Vol 3• Sicher And Dubrul’s Oral Anatomy• RODRIGUES, Antonio de Castro et al. Anatomy of the

Facial Nerve and its Implication in the Surgical Procedures. Int. J. Morphol. [online]. 2009, vol.27, n.1

• Gulam Hasan, Ashfaqul Hasan,Kulbeer Kaur, Muzaffar Ahmad, Mohd. Shafi, The Facial Nerve : The Anatomical and Surgical important,JK-Practitioner2005;12(1):53-57

• Mark May , Barry M. Schaitkin The facial nerve 2nd edition

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