Facial nerve

facial nerve and its applied in dentistry

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2. FACIAL NERVE 2

3. Introduction Embryology & Nuclei of origin Course & Relations Branches of facial nerve Functional components Ganglia associated with facial nerve Blood supply Applied Aspect CONTENTS 3

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5. 7 th cranial nerve Mixed nerve It emerges from the brain stem between the pons and the medulla. Function- Conveys taste sensation from anterior 2/3 rd of tongue and oral cavity and also , controls the muscles of facial expression . Supplies- preganglionic parasympathetic fibres to several head and neck ganglia 5 Sensory root Motor root

6. Embryology The facial nerve is developmentally derived from the hyoid arch , which is the second branchial arch. It arises as 2 main divisions- motor and sensory The motor division of facial nerve is derived from the basal plate of the embryonic pons The sensory division originates from the cranial neural crest 6

7. Facial nerve course, branching pattern, and anatomical relationships are established during the first 3 months of prenatal life The nerve is not fully developed until about 4 years of age. The first identifiable Facial Nerve tissue is seen at the third week of gestation- facioacoustic primordium or crest 7

8. FACIAL NERVE EMBRYOLOGY: 4 TH WEEK By the end of the 4 th week, the facial and acoustic portions are more distinct The facial portion extends to placode The acoustic portion terminates on otocyst 8

9. FACIAL NERVE EMBRYOLOGY: 5 TH WEEK Early 5 th week, the geniculate ganglion forms from distal part of primordium It separates into 2 branches : main trunk of facial nerve and chorda tympani 9

10. FACIAL NERVE EMBRYOLOGY: 6 TH WEEK Near the end of the 5 th week, the facial motor nucleus is recognizable The motor nuclei of VI and VII cranial nerves initially lie in close proximity. The internal genu forms as metencephalon , it elongates and CN VI nucleus ascends 10

11. FACIAL NERVE EMBRYOLOGY: 7 TH WEEK Early 7 th week, geniculate ganglion is well-defined and facial nerve roots are recognizable The nervus intermedius arises from the ganglion and passes to brainstem. Motor root fibers pass mainly caudal to ganglion 11

12. Proximal branches form in the 6 th week , posterior auricular branch, branch of digastric Early 8 th week temporofacial and cervicofacial divisions present Late 8 th week , 5 major peripheral subdivisions present 12

13. NUCLEI OF ORIGIN 13

14. FUNCTIONAL COMPONENT NUCLEI DISTRIBUTION FUNCTION GVE Superior salivatory nucleus (lies in the pons lateral to the main motor nucleus of VII ) Submandibular and sublingual salivary glands. Preganglionic Secretomotor SVE Motor nucleus of facial nerve (lies in lower part of pons) Muscles of facial expression, stylohyoid , posterior belly of digastric, platysma and stapedius . Facial expression SVA Nucleus of tractus solitarius (lies in medullla ) Taste buds in the anterior 2/3 rd of tongue except vallate papillae. Taste sensations GSA Spinal nucleus of Vth nerve Part of skin of external ear. Exteroceptive sensation 14

15. COURSE OF FACIAL NERVE 15

16. The course of facial nerve is divided by stylomastoid foramen into INTRACRANIAL INTRAPETROUS PART EXTRACRANIAL PART 16

17. The nerve arises in the  pons in brainstem . It begins as two roots; a large  motor root , and a small  sensory root   (Nervous intermedius ) The two roots travel through the internal acoustic meatus. 17

18. W ithin the temporal bone, the roots leave the internal acoustic meatus, and enter into the  facial canal (‘Z ’ shaped) .   The two roots  fuse  to form the facial nerve. T he nerve forms the   geniculate ganglion The nerve gives rise to the  greater petrosal nerve   (parasympathetic fibres to glands), the nerve to  stapedius   (motor fibres to stapedius muscle), and the   chorda tympani   (special sensory fibres to the anterior 2/3 tongue). 18

19. The facial nerve then exits the facial canal (and the cranium) via the   stylomastoid foramen , located just posterior to the styloid process of the temporal bone 19

20. 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 . 20

21. The main trunk of the nerve  ( motor root  of the facial nerve), continues anteriorly and inferiorly into the   parotid gland.   Within the parotid gland, the nerve terminates by splitting into five branches: Temporal branch Zygomatic branch Buccal branch Marginal mandibular branch Cervical branch These branches are responsible for innervating the muscles of facial expression. 21

22. Branches Branches of communication Branches of distribution

23. BRANCHES OF DISTRIBUTION 23

24. I- WITHIN THE FACIAL CANAL: 1- Nerve to stapedius : supplies the stapedius muscle . 2- Greater superficial petrosal nerve (GSPN) : arises from the geniculate ganglion. 3- Chorda tympani nerve : It arises from the facial nerve 6 mm above the stylomastoid foramen and runs upwards to perforate the posterior bony wall of the tympanic cavity. 24

25. It then passes forwards on the medial surface of the tympanic membrane It comes out of the tympanic cavity through the petrotympanic fissure to the infratemporal fossa where it joins the lingual nerve. Through the lingual nerve, it supplies both the submandibular and sublingual salivary glands by secretomotor fibres and taste fibers from the anterior 2/3 of the tongue 25

26. II- AT THE EXIT FROM THE STYLOMASTOID FORAMEN 1- Posterior auricular nerve : to the auricularis posterior and occipitalis muscle. 2- Digastric branch : to the posterior belly of digastric muscle 3- Stylohyoid branch : to the stylohyoid muscle 26

27. III- TERMINAL BRANCHES 27

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29. 29 Elevates upper lip Smile Snoring THE BUCCAL BRANCH SUPPLIES:

30. 30 Moves skin of forehead Flare nostrils closes the mouth, puckers the lips chewing smile

31. Internal acoustic meatus Vestibulocochlear nerve Geniculate ganglion Greater petrosal nerve Lesser petrosal nerve External petrosal nerve Facial canal Vagus nerve Stylomastoid foramen IX & X cranial nerve Greater auricular nerve Auriculotemporal nerve Behind ear Lesser occipital Face V nerve Neck Transverse cutaneous nerve Branches of Communication 31

32. GANGLIA ASSOCIATED WITH THE FACIAL NERVE 32

33. GENICULATE GANGLION Derived from Latin GENU = "KNEE“ L-shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head. Receives fibers from the motor, sensory , and parasympathetic components of the facial nerve 33

34. Innervates Lacrimal glands Submandibular glands Sublingual glands Tongue Palate Pharynx External auditory meatus Stapedius Posterior belly of the digastric muscle Stylohyoid muscle Muscles of facial expression. 34

35. SUBMANDIBULAR GANGLION Small and fusiform in shape. Situated above the deep portion of the submandibular gland, on the hyoglossus muscle , near the posterior border of the mylohyoid muscle. The ganglion 'hangs' by two nerve filaments from the lower border of the lingual nerve one anterior and one posterior . Through the posterior of these it receives a branch from the chorda tympani nerve which runs in the sheath of the lingual nerve. 35

36. PTERYGOPALATINE GANGLION The P terygopalatine ganglion ( meckel's ganglion, nasal ganglion or sphenopalatine ganglion ) - parasympathetic ganglion found in the pterygopalatine fossa. It's largely innervated by the greater petrosal nerve (a branch of the facial nerve); and its axons project to the lacrimal glands and nasal mucosa 36

37. FACIAL NERVE BLOOD SUPPLY The facial nerve gets it’s blood supply from Anterior inferior cerebellar artery – at the cerebellopontine angle Labyrinthine artery  (branch of anterior inferior cerebellar artery) – within internal acoustic meatus Superficial petrosal artery (branch of middle meningeal artery) – geniculate ganglion and nearby parts 37

38. Stylomastoid artery ( branch of posterior auricular artery) – mastoid segment Posterior auricular artery supplies the facial nerve at & distal to stylomastoid foramen 38

39. Child Adult Chorda tympani may exit through Stylomastoid Foramen Chorda tympani exit proximal to Stylomastoid Foramen Nerve trunk is more anterior and lateral on exit through Stylomastoid Foramen Nerve trunk is less anterior and deeper Nerve more superficial over angle of mandible Nerve less superficial over angle of mandible AGE CHANGES 39

40. APPLIED ASPECT 40

41. DISORDERS OF FACIAL NERVE Facial nerve lesions: Supra-nuclear type Nuclear type Peripheral lesions Injury at internal acoustic meatus Injury distal to geniculate ganglion Injury at stylomastoid foramen 41

42. 1. SUPRA NUCLEAR TYPE: Features : Paralysis of lower part of face (opposite side) Partial paralysis of upper part of face Normal taste and saliva secretion Stapedius not paralysed 42

43. NUCLEAR TYPE: Features : Paralysis of facial muscle (same side) Paralysis of lateral rectus 43

44. PERIPHERAL LESION At internal acoustic meatus Features : Paralysis of secretomotor fibers Hyper acusis Loss of corneal reflex Taste fibers unaffected Facial expression and movements paralysed 44

45. Injury distal to geniculate ganglion Features : Complete motor paralysis (same side) No hyper acusis Loss of corneal reflex Taste fibers affected Facial expression and movements paralysed . 45

46. Injury at stylomastoid foramen Condition known as Bell’s Palsy 46

47. CAUSES OF FACIAL PALSY 47

48. BIRTH Forceps delivery Dystrophia myotonica Moebius ' syndrome (facial diplegia associated with other cranial nerve deficits ) TRAUMA Basal skull fracture Facial injuries Penetrating injury to middle ear Altitude paralysis (barotrauma) Scuba diving (barotrauma) 48

49. 49 INFECTIONS External otitis Otitis media Mastoiditis Chicken pox Herpes zoster (Ramsay Hunt syndrome) Encephalitis Poliomyelitis (type I) Mumps Leprosy Coxsackievirus Malaria Syphilis Scleroma Tuberculosis Botulism Mucormycosis Lyme disease

50. 4.TOXIC 5.METABOLIC 50 Thalidomide ( Miehlke syndrome, cranial nerves VI, VII with congenital malformed external ears and deafness) Tetanus Diphtheria Carbon monoxide Diabetes mellitus Hyperthyroidism Pregnancy Hypertension Acute porphyria

51. 6.NEOPLASTIC 7th nerve tumour Leukaemia Meningioma Haemangioblastoma Sarcoma Carcinoma (invading or metastatic) Haemangioma of tympanum Facial nerve tumour ( cylindroma ) Schwannoma Teratoma Fibrous dysplasia von Recklinghausen's disease 51

52. 7. IATROGENIC 8. IDIOPATHIC 52 Mandibular block anesthesia Head and neck surgery Myasthenia Gravis Guillain-Barre Syndrome Sarcoidosis Familial Bell's Palsy

53. BELL’S PALSY 53

54. Background of BELL’S PALSY First described more than a century ago by Sir Charles Bell Controversy still surrounds its etiology and management Bell palsy is certainly the most common cause of facial paralysis worldwide 54

55. DEMOGRAPHICS OF BELLS PALSY Race: slightly higher in persons of Japanese descent . Sex: No difference exists Age: highest in persons aged 15-45 years. Bell palsy is less common in those younger than 15 years and in those older than 60 years. 55

56. Pathophysiology of Bells palsy Main cause of Bell's palsy is latent herpes viruses (herpes simplex virus type 1 and herpes zoster virus), which are reactivated from cranial nerve ganglia Polymerase chain reaction techniques have isolated herpes virus DNA from the facial nerve during acute palsy 56

57. Unilateral involvement Inability to smile, close eye or raise eyebrow Whistling impossible Drooping of corner of the mouth Inability to close eyelid (Bell’s sign) Inability to wrinkle forehead Loss of blinking reflex Slurred speech Mask like appearance of face Loss/ alteration of taste FEATURES OF BELL’S PALSY 57

58. MANAGEMENT OF BELLS PALSY It focuses on protecting the cornea from drying and abrasion due to problems with lid closure and the tearing mechanism . Lubricating drops should be applied hourly during the day and a simple eye ointment should be used at night. EYE CARE 58

59. Treatment consists of Infra-red radiation on affected side of the face at 2 ft (60cm) ,followed by interrupted galvanism on affected side Treatment was given daily at first few weeks & later thrice weekly. All patients are instructed to massage the face daily 70-80% of these patients recover completely, while the reminder develop various sequelae within one to three months 59

60. MEDICAL TREATMENT Corticosteroids : Prednisolone 1 mg/kg/day 7-10 days Corticosteroids combine with antiviral drug is better Acyclovir 400 mg 5 times/day Famciclovir and valacyclovir 500 mg bid 60

61. SURGICAL TREATMENT Facial nerve decompression Indication: Completely paralysis Appropriate time for surgery is 2-3 weeks after paralysis 61

62. FACIAL NERVE PARALYSIS Most commonly during inferior alveolar nerve block or infraorbital nerve block Cause LA into the capsule of the parotid gland Prevention Use of proper technique Avoid over insertion of needle Treatment Transient, self correcting with 3 hours or less. 62

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64. Gray's Anatomy By Richard Drake, A. Wayne Vogl , Adam W. M. Mitchell. A.K. Datta Essentials Of Human Anatomy Head And Neck. 4 th Edition B D CHAURASIA’S Human Anatomy. Volume 3 Edition 4th Atlas Of Anatomy Edited By Anne M. Gilroy, Brian R. Macpherson, Lawrence M. Ross Monheim’s Local Anaesthesia And Pain Control In Dental Practice 64 REFERENCES

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