Facial Nerve Lecture Notes PDF

Facial nerve -The facial nerve is a mixed nerve, as it contains motor, sensory and autonomic fibers. -Anatomy of the motor part: ✓ The motor nucleus of the facial nerve is in the pons. ✓ The upper part of the nucleus is bilaterally supplied from the pyramidal tracts of both sides, whi...

Facial nerve -The facial nerve is a mixed nerve, as it contains motor, sensory and autonomic fibers. -Anatomy of the motor part: ✓ The motor nucleus of the facial nerve is in the pons. ✓ The upper part of the nucleus is bilaterally supplied from the pyramidal tracts of both sides, while its lower part is unilaterally supplied from the pyramidal tract of the opposite side only ✓ From the nucleus, the motor fibers pass through the cerebello-pontine angle near Cr.N. V &VIII → then enter through the internal auditory meatus, into the facial canal where it becomes adherent to its sensory and autonomic parts. ✓ It then leaves the canal through the stylomastoid foramen, passes through the parotid gland to divide into its terminal branches that supply the following muscles. Muscles of expression Other muscles 1. Frontalis 1. Platysma. 2. Oricularis oculi 2. Stapedius 3. Orbicularis oris 3. Posterior belly of thedigastric 4. Buccinator muscle. 5. Retractor anguli 4. Stylohyoid. Anatomy of the sensory and autonomic parts: ✓ In the facial canal lies the geniculate ganglion, which contains unipolar cells. ✓ The process of these cells divides in a T-shaped manner into a peripheral branch and a central branch. 1. The peripheral branch runs laterally and divides into the greater superficial petrosal nerve and the chorda tympani. a. The greater superficial petrosal (GSP) nerve passes forwards to relay in the sphenopalatine ganglion where a new set of fibers gives autonomic supply to the lacrimal gland. b. The chorda tympani leave the facial nerve before the stylomastoid foramen, to supply the submaxillary and sublingual salivary glands and to carry taste sensations from the anterior 2/3 of the tongue. 2. The central branch ✓ passes centrally ✓ joins the motor part of the nerve, then enters the cranial cavity through the internal auditory meatus as the nervus intermedius→ enters the brain stem → terminate in the solitary nucleus in the medulla. ✓ A new set of fibers passes from the nucleus to the opposite side and runs upwards to terminate in the lower part of the cortical sensory area, where taste sensation from the anterior 2/3 of the tongue is perceived By/ Samar U.M.N.L L.M.N. L Affecting Δ tract above facial nucleus. Affecting the facial motor nucleus or the nerve itself. Paralysis of the muscles of the lower half of the face on the Paralysis of the upper & lower halves of the face muscles opposite side of the lesion (supplied from the opposite ∆ tract on the same side of the lesion leading to: only) leading to: a →e and in addition: a. Obliteration of the naso-labial fold. f.Inability to raise the eyebrows with absence of wrinkles b. Dropping of the angle of the mouthwith dribbling of saliva. of the forehead. c. Accumulation of food behind the cheeks. g. Inability to close the eye, when the pt. attempts to D. Inability to blow the cheeks. close his eye the eyeball rolls upwards (Bell's e.Inability to show the teeth properly. phenomenon). Paralysis involves voluntary movement; it spares the Paralysis affects voluntary, emotional & associative emotional & associative movements (which are supplied by movements. extra ∆ fibers). There is associated hemiplegia on the same side of the facial If there is hemiplegia, it is on the opposite side of the paralysis. facial paralysis (crossed hemiplegia). Facial Taste Salivation Site of lesion Other Features Cause muscles sensation. lacrimation Vascular: Vertebro -basilar insuff Millard -Gubler syndrome. Infective: Hemiplegia on Nuclear lesion Paralyzed Intact Intact Encephalitis. opposite side Poliomyelitis. Neoplastic: Astrocytoma or Glioma Demyelinating M. S. Infective: Basal meningitis. Cranial nerves Cerebello -pontine Neoplastic: Paralyzed ↓ ↓ 5 and 8 palsies lesion Acoustic neuroma. on same side Meningioma Traumatic: Fracture base. Lacrimation↓ If Infective: the GSP nerve is ↓ if chorda Otitis media. involved. Facial canal lesion Paralyzed tympani is Herpes zoster. Salivation↓ if involved. Neoplastic chorda tympani is Facial neuroma. involved. Bell's palsy. Neuropathy: DM Extra-cranial Facial Myopathy: Lesion: After its exit Paralyzed Intact Intact Intact Facio scapulo-humeral. from the stylo- Myotonia Atrophica. mastoid foramen. Neoplastic: Parotid tumor By/ Samar  Bell’s palsy Definition: It is an acute paralysis of the facial nerve near the stylomastoid foramen (i.e. LMN). It is usually unilateral, maybe recurrent & sometimes runs in families. Etiology: 1. Exposure to air drafts usually precedes the onset; this may lead to ischaemia, oedema & compression of the nerve at the stylomastoid foramen. 2. It may be 2ry to a neurotropic virus e.g. Herpes zoster. 3. It may be autoimmune, as evidenced by high levels of immunoglobulins in the patient's serum. Clinical Picture: The onset is usually acute with pain behind the ear → One or two days later, there is complete paralysis of the facial muscles on the affected side of L.M.N. nature. Treatment: 1. Medical: a) Oral steroids b) Protection of the exposed cornea. 2. Physiotherapy 3. Surgical: a) Decompression of the facial nerve. b) Facial nerve grafting. Prognosis: Full recovery occurs in about 80% of the cases, 15% experience some kind of permanent nerve damage and 5% remain with severe sequelae. Poor prognostic factors: ✓ Complete palsy or severe degeneration (electrophysiology). ✓ No signs of recovery by three weeks. ✓ Age >60. ✓ Severe pain. ✓ Ramsay Hunt's syndrome (herpes zoster virus). ✓ Associated with either hypertension, diabetes, or pregnancy. Those with axonal degeneration may not show any reinnervation for three months and recovery may be partial or not at all. Synkinesis is often seen e.g. blinking causes the angle of the mouth to contract. Also aberrant parasympathetic re-innervation may cause symptoms such as gustatory lacrimation ('crocodile tears') By/ Samar