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Facial Nerve

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Facial Nerve Facial nerve 7TH CARNIVAL NERVE Synopsis Introduction Nuclei Anatomical course Branches and it’s distribution FUNCTIONAL COMPONENTS 1. Motor function 2. Special sensory function 3. Parasympathetic functions Ganglia Clinical Relevance INTRODUCTION The facial nerve, CN VII, is the seventh paired cranial nerve. In this article, we shall look at the anatomical course of the nerve, and the motor, sensory and parasympathetic functions of its terminal branches. The facial nerve is associated with the derivatives of the second pharyngeal arch. NUCLEI The fibers of the nerve are connected to four nuclei situated in the lower pons 1. Motor nucleus or branchiomotor 2. Superior salivatory nucleus or parasympathetic 3. Lacrimatory nucleus is also parasympathetic 4. Nucleus to the tractus solitarius The motor nucleus lies deep in the reticular formation of lower pons. The part of nucleus that supplies muscles of upper part of face receives cortico nuclear fibers from motor cortex of both right and left side ANATOMICAL COURSE I Intacranial course: The facial nerve is attached to the brain stem by two roots ,motor and sensory.The sensory root is also called the nerves intermedius The two roots of facial nerve are attached to the later part of the lower border of the pons just medial to the eighth cranial nerve. The two roots run laterally and forwards , with the eighth nerve to reach the internal acoustic meatus In the meatus , the motor root lies in a groove on the eighth nerve, with the sensory root intervening.Here the seventh and eighth nerves are accompanied by labyrinthine vessels. Within the canal , the course of the nerve can be divided into three parts by two bends 1. The first bend at the junction of the first and second parts in sharp. It lies over the anterosuperior part of the promontory and is also called genu 2. The second bend is gradual, and lies between the promontory and Aditus to the mastoid antrum 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 forward through the galnd crossing the retromandibular Beni and external carotid artery. Behind the neck of mandible. It divides into its five terminal branches which emerge along the anterior border of the parotid galnd BRANCHES AND IT’S DISTRIBUTION Within the facial canal 1. Greater petrosal nerve 2. Nerve to stapedius 3. The chorda tympanic At its exit the stylomastoid forame: 1. Posterior auricular 2. Diagastric 3. Stylohyoid Terminal branches within the parotid gland 1. Temporal 2. Zygomatic 3. Buccal 4. Marginal mandibular 5. Cervical The nymonic FUNCTIONAL COMPONENTS Motor function: Branches Of the facial nerve are responsible for innervation of many muscle of the head and neck.All are muscles are derviatives Of second phrengeal arch. 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. Temporal branch – Innervates the frontalis, orbicularis oculi and corrugator supercilii Zygomatic branch – Innervates the orbicularis oculi. Buccal branch – Innervates the orbicularis oris, buccinator and zygomaticus muscles. Marginal Mandibular branch – Innervates the mentalis muscle. Cervical branch – Innervates the platysma. The terminal branches of facial nerve Special sensory functions The chorda tympani branch of the facial nerve is responsible for innervatingthe 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. Parasympathetic 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 thenerve 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. 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. Clinical relevance Clinical Relevance: Damage to the Facial Nerve The Facial nerve has a wide range of of Functions...thus damage to the facial nerve can produce vari ous set of symptoms, depending on the site of lesion INTRACRANIAL LESION Intracranial Lesion occurs during intracranial course Of facial nerve ( proximal to the stylomastoid Foramen The muscles facial expressions will be Paralysed or severally weakened. The other symptoms produced depend on the location of lesion, and the branches that are affected 1. Chorda tympani- reduced salivation and loss of taste On the ipsilateral 2/3 of tongue 2. Nerve to sapedius- ipsilateral hyperacusis 3. Greater petrosal nerve – ipsilateral reduced reduced lacrimal fluid production Extracranial Lesions Extarcranial lesion occur during the extracranial course of the facial nerve .only the motor function of the facial nerve is affected, therefore resulting in the paralysis or severe weakness of the muscles of facial expression. Parotid gland pathology- eg :a tumor, parotitis , surgery Infections of the nerve- particularly by the Herpes virus Comprssion during forceps delivery – the neonatal mastoid process is not. Fully developed , and does not provide complete protection of the nerve BELL’S PALSY In bell‘s palsy, the upper and lower quarters of the face on the same side get paralysis.The face becomes asymmetrical and is drawn up to the normal side. The affected side is motionless. Wrinkles disappear from the forehead. The eyes cannot be close. Any attempt to smile draws the mouth to the normal side. During mastication , food accumulated between the teeth and the cheek. Articulation of labials is impaired Reference from K.Sembulingam B.D chaurasia ‘s Teach me anatomy app This topic was inspired by Priyadarshini mam (special thanks) .
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