Facial nerve and its extracranial and intracranial rots

facial nerve its origin and insertion and its extracranial and intracranial roots and its branches and clinical significance and its related syndromes explained well along with treatment plan

1. 1 Good M o r n i n g … 

2. FACIAL NERVE Dr. Sonam Bohra Department Of Conservative Dentistry & Endodontics

3. CONTENTS 3 INTRODUCTION INTRODUCTION TO FACIAL NERVE EMBRYOLOGY NUCLEI OF ORIGIN FUNCTIONAL COMPONENTS COURSE BRANCHES AND DISTRIBUTION GANGLIA BLOOD SUPPLY SURGICAL ANATOMY OF FACIAL NERVE APPLIED ASPECTS CONCLUSION BIBLIOGRAPHY

4. uses A bundle of fibers tha t e l ectric a l and chemical si g na l s to transmit sensory and motor information from one body part to another. WHAT IS A NERVE? 4

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6. Sensory 1 & 2 to the forebrain 3 & 4 to the mid brain 5, 6, 7, 8 to the pons 9, 10, 11, 12 to the medulla oblongata Brain stem Motar Mixed 1, 3, & 8 2, 4, 6, 11, 12 5, 7, 9, 10

7. INTRODUCTION TO FACIAL NERVE 8 There are 12 cranial nerves. The Facial nerve is the 7 th cranial nerve. It is the nerve of the second branchial arch . Hence supplies all the muscles that develop from the mesoderm of this arch. It is a mixed nerve with a large motor root and a small sensory root ( nervus intermedius)

8. Diameter of facial nerve axons varies between 3-20µm and the nodes of ranvier are spaced from 0.1-1.8µm apart. Because facial nerve fibers are myelinated the wave of depolarization can jump from one node of ranvier to the next, a process called saltatory conduction . This accounts for the rapid conduction velocity of the facial nerve, which is 70-110m/sec . 9

9. EMBRYONIC DEVELOPMENT OF FACIAL NERVE 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 13

10. EMBRYOLOGY OF FACIAL NERVE 11 Weeks Features 0-4 Appearance of facio-acoustic primordium/crest Splitting of facial nerve Presence of chorda tympani 5-6 Separation of facial and acoustic nerves Appearance of geniculate ganglion Formation of GPN 7 Formation of peripheral branches 8 Formation of fallopian canal 10-15 More extensive branching

11. NUCLEI OF ORIGIN AND THEIR COMPONENTS 12 1. Motor nucleus Upper face recieves bilateral innervation. lower face receives unilateral innervation. Muscles of facial expression. posterior belly of digastric. stylohyoid muscle. stapedius. 2. Lacrimatory and 3. Superior salivatory nucleus lacrimal gland Submandibular & sublingual salivary glands Both are parasympathetic 4. Nucleus of solitary tract ( gustatory nucleus) Mediates taste

12. FUNCTIONAL COMPONENTS 16 SPECIAL VISCERAL SPECIAL VISCERAL GENERAL SOMATIC EFFERENT AFFEREBT GENERAL VISCERAL GENERAL VISCERAL

13. Branchial motor (special visceral efferent ) supply the muscles derived by the mesoderm of II branchial arch which are the muscles of facial expression; occipitofrontalis; posterior belly of digastric muscle; stylohyoid, and stapedius. Visceral motor (general somatic efferent ) Originates in superior salivatory nucleus and Parasympathetic innervation of the Secretomotar to lacrimal, submandibular, and sublingual glands, mucous membranes of nasopharynx, hard and soft palate. F U NCTIONAL COM P ONENT S - moto r 17

14. Special sensory (special visceral afferent ) Taste sensation from the Anterior 2/3 of tongue Hard and soft palates . General sensory (general somatic afferent ) General sensation from the skin of the ear external acoustic meatus and deeper parts of the auricle. But it does not gives any direct branch to ear FUNCTIONAL COMPONENTS - sensory 15

15. COURSE 16 Intra cranial course Intra pontine course Attachment to the brain stem Course through posterior cranial fossa Exit from the cranium Extracranial course Intrapetrous course Meatal part Facial canal part labyrinthine segment Tympanic segment Mastoid segment

16. Intrapontine Course : T h e fib e rs from th e m o t or n u c l e us course through the sh a r p b e n d a r o u nd pon s taki n g a the abducent nucleus producing internal genu of the facial nerve and they leave the pons between the nucleus of spinal tract of trigeminal and the other facial nucleus. INTRACRANIAL COURSE 17

17. Attachment to the brain stem : The sensory and motor roots are attached to the lateral aspects of the pontomedullary junction . INTRACRANIAL COURSE 18

18. Course Through Posterior Cranial Fossa The two roots of facial nerve run laterally and forward along with 8 th cranial nerve & labyrinthine artery & These structures together enter the internal acoustic meatus in the post-cranial fossa. INTRACRANIAL COURSE 19

19. Meatal segment : It is in the internal acoustic meatus where the motor root is l ies in a groove on the antero-inferior surface of the vestibulochoclear nerve but the sensory root separates them. At the bottom of the internal acoustic meatus , the two roots unite to form the trunk of the facial nerve and then it enters the facial canal. INTRAPETROUS COURSE 20

20. i. L ab y r i nt h i n e s e g m e n t : passes laterally above the vestibule of the inner ear to reach the anterior end of the medial wall of the middle ear. Here it bends backwards at a sharp turn called the external genu of the facial nerve which has the geniculate ganglion on it. Facial canal part : is divided into 3 segments : INTRAPETROUS COURSE 21

21. ii. Tympanic segment : passes backwards in the medial wall of the middle ear till it reaches the posterior end of this wall. It is also known as the horizontal part . INTRAPETROUS COURSE 22

22. i i i . Mast o id s e g m en t or segment : vertical begins at the posterior end of the medial wall and passes downwards in relation to the posterior wall of the middle ear to reach the stylomastoid foramen. INTRAPETROUS COURSE 23

23. EXIT FROM THE CRANIUM The facial nerve leaves the cranium through stylomastoid foramen 27

24. The facial nerve crosses the lateral side of the base of the styloid process. It enters the posteromedial surface of the parotid gland . EXTRACRANIAL COURSE 25

25. Within the gland it runs forward for a short distance superficially to the retromandibular vein and external carotid artery and then divides into a)Temprofacial and b)Cervicofacial trunks. EXTRACRANIAL COURSE 26

26. Temporofacial and Cervicofacial Trun k s. EXTRACRANIAL COURSE 27

27. The terminal branches radiate like a goose’s foot from the anterior border of the parotid gland – “ Pes anserinus ” EXTRACRANIAL COURSE 28

28. BRANCHES AND DISTRIBUTION 29 Within the facial canal: Greater petrosal nerve Nerve to stapedius Chorda tympani nerve At the exit from the styomastoid foramen: Posterior auricular nerve Nerve to the digastric Nerve to stylohyoid

29. Terminal branches within the parotid gland: Temporal nerve Zygomatic nerve Buccal nerve Marginal mandibular Cervical branch IV . Com m u n i ca ting branche s with ad j ace n t cranial and spinal nerves 30

30. Within the facial canal 31

31. Greater Petrosal Nerve 35

32. Carries gustatory and parasympathetic fibers. Greater Petrosal Nerve 33 Arises from the geniculate ganglion of the facial nerve , and enters the middle cranial fossa through the hiatus for the greater petrosal nerve on the anterior surface of the petrous temporal bone. It proceeds towards the foramen lacerum where it joins the deep petrosal nerve which carries sympathetic fibers to form nerve of petrygoid canal.

33. The nerve of the pterygoid canal passes through the pterygoid canal to reach the pterygoplatanine ganglion. The parasympathetic fibers relay in this ganglion. Postganglionic parasympathetic fibers arising in the ganglion ultimately supply the lacrimal gland and the mucosal glands of the nose, palate and pharynx . The gustatory or taste fibers do not relay in the ganglion and are distributed to the palate. Greater Petrosal Nerve 34

34. Arises opposite the pyramid of the middle ear , and supplies the stapedius muscle. The muscle damps excessive vibrations of the stapes caused by high- pitched sounds. Nerve To The Stapedius 35

35. It runs upwards and forwards in a bony canal. It enters the middle ear and runs forwards in close relation to the tympanic membrane. Arises in the vertical part of the facial canal about 6mm above the stylomastoid foramen. The Chorda Tympani 36

36. It leaves the middle ear by passing through pterygopalatine fissure. It then passes medial to the spine of the sphenoid and enters the infratemporal fossa. Here it joins the lingual nerve through which it is distributed. It carries the preganglionic fibres to the submandibular and sublingual salivary glands and taste fibres from the anterior two-thirds of the tongue. The Chorda Tympani 37

37. At The Exit From The Stylomastoid Foramen 41

38. Posterior auricular nerve 42 Arises just below the stylomastoid foramen. It ascends between the mastoid process and the external acoustic meatus and supplies: The posterior auricularis The occipitalis The intrinsic muscles on the back of the auricle. POSTERIOR AURICULAR BRANCH

39. The digastric branch Arises close to the posteriorauricular nerve. It is short and supplies the posterior belly of digastric . 43

40. Stylohyoid branch It arises with the digastric branch. It is long and supplies the stylohyoid muscle. 44

41. Terminal branches within the parotid gland 42

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43. Com m u n i ca ting branche s with ad j ace n t cranial and spinal nerves For the effective co ordination between the movements of muscles of 1 st , 2 nd and 3 rd brachial arches the motor nerve of three arches communicate with each other

44. Gangli a Ass o ciate d Wit h Facia l Nerv e 48

45. Ganglia Associated With Facial Nerve I. 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 fibers present in the nerve are present in the genigulate ganglion. 46

46. II. SUBMANDIBULAR GANGLION : - is a parasympathetic ganglion for relay of secretomotor fibers to the submandibular and sublingual salivary glands. 47

47. iii. PTERYGOPLATINE GANGLION (SPHENOPALATINE GANGLION): 48

48. iii. PTERYGOPLATINE GANGLION (SPHENOPALATINE GANGLION): Is the largest parasympathetic peripheral ganglion . It serves as a relay station for secretomotor fibers to the lacrimal gland and to the mucous glands of the nose,paranasal sinuses,palate and the pharynx. It is also called hay fever ganglion. 49

49. BLOOD SUPPLY 50 The facial nerve gets it’s blood supply from 4 vessels : . 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 Stylomastoid artery (branch of posterior auricular artery) – mastoid segment

50. FUNCTION 51 The facial nerve is responsible for: -Contraction of the muscles of the face -Production of tears from a gland (Lacrimal gland) -Conveying the sense of taste from the anterior 2/3rd of the tongue (via the Chorda tympani nerve) -The sense of touch at auricular conchae

51. CLINICAL RELEVANCE- DAMAGE TO THE FACIAL NERVE 52

52. Three Degrees of Facial Nerve Fiber Injury 53

53. Three Degrees of Facial Nerve Fiber Injury 54

54. Level Of Nerve Injury And Symptoms 55

55. FACIAL PARALYSIS 56

56. Paresis : weakness of facial muscles to perform motor functions is called paresis ( partial dysfunction) Paralysis: Total flaccidity of facial muscles to perform a motor function is called facial paralysis 57

57. SUPRANUCLEAR FACIAL PARALYSIS It is usually hemiplegia- T he lower part of the face of opposite side that is chiefly affected, while the upper part remains unaffected, i.e , the frontalis and orbicularis oculi muscles escape. because upper part has bilateral control 58

58. INFRA NUCLEAR FACIAL PARALYSIS The lower motor neuron lesion of facial nerve cause paralysis of all facial muscles on the same side . In LMN injury both the upper and lower parts will be involved 67

59. HOUSE-BRACKMAN(1985) CLASSIFICATION FOR FACIAL FUNCTION 60 Grade I-normal function without weakness. Grade II-mild dysfunction with slight facial asymmetry with a minor degree of synkinesis. Grade III-moderate dysfunctions-obvious , but not disfiguring, asymmetry with contracture and/or hemifacial spasm,but residual forehead motion and incomplete eye closure. Grade IV-moderately severe dysfunction- obvious, disfiguring asymmetry with lack of forehead motion and incomplete eye closure. Grade V-severe dysfunction-asymmetry at rest and only slight facial movement. Grade VI-total paralysis-complete absence of tone or motion.

60. BELL’S PALSY It is defined as an idiopathic paresis or paralysis of the facial nerve of sudden onset. The name was ascribed to SIR CHARLES BELL , who in 1821 demonstrated the separation of motor and sensory innervation of face. 61

61. IN C ID E N C E - 62 15-40 cases per 1 lakh cases S E X P R E D I LE C T I O N- wom e n m o r e a f f e ct e d t han me n. 3.3 m o re t i m e s co m mon i n pr eg n a ncy a nd i n t h e th i rd trimester. AG E - can oc c ur a t an y ag e , c o m m on i n m i d dl e aged people. SIDE INVOLVMENT- can be equally seen, usually unilateral.

62. CLINICAL FEATURES 63

63. CLINICAL FEATURES 64 Inability to smile, close eye and raise eyebrow. Whistling is impossible Drooping of corners of the mouth. Slurred speech Inability to close eyelid (Bell’s sign) Loss of blinking reflex Inability to wrinkle forehead Mask like appearance of the face. Loss or alteration of taste.

64. COURSE AND PROGNOSIS Partial paralysis always resolves completely within a few weeks. Recovery from complete paralysis takes longer (months) and is complete in only about 60-70% of cases. Approximately 15% of patients are left with troublesome residual palsy . 65

65. RAMSAY HUNT SYNDROME A special form of herpes zoster infection of the geniculate ganglion with the involvement of the external ear , eye, and the oral mucosa 66

66. MELKERSSON ROSENTHAL SYNDROME Recurrent attacks of facial paralysis Associated with multiple episodes of non-pitting, non-inflammatory painless edema of the face Chelitis granulomatosa Fissured tongue 67

67. MOBIUS SYNDROME Results from the underdevelopment of cranial nerve VI and VII The VI cranial nerve controls lateral eye movement, and the VII cranial nerve controls facial expression and is manifested in infancy. 68

68. MOBIUS SYNDROME Because of partial or complete facial paralysis, the infant exhibits : N o change in facial expression ( mask like appearance ) Failure to close eyes during sleep . Mouth may remain partially open 69

69. CROCODILE TEARS SYNDROME Due to injury to facial nerve proximal to the geniculate ganglion, ther e m a y be nerve fibres a m i sdi re cti o n of to l ac r i mal g l a nd instead of going to submandibular gland, through the greater petrosal nerve. As a result patient lacrimates is termed as ‘ crocodile tear syndrome ’ and can be treated by dividing greater petrosal nerve. 70

70. CLINICAL NOTES Parotid disease: Parotid tumours, surgery m a y d a ma g e b r anches of t r au m a or t he facial nerve. This would result in an ipsilateral facial palsy with wasting and functional loss. It would be unlikely to recover. PATEY’S OPERATION 71

71. CLINICAL NOTES 72 Stapedial hyperacusis: Dysfunction of the smallest muscle supplied by the facial nerve can cause a distressing symptom. Stapedius dampens the movements of the ossicular chain and if it is inactive, sounds will be distorted and echoing. This is hyperacusis.

72. ⚫ This branch passes on or just below the lower margin of the mandible. It is superficial even to the palpable facial arterial pulse and is thus liable to injury. The marginal mandibular branch of the facial nerv e : CLINICAL NOTES 73

73. CLINICAL NOTES 74 The marginal mandibular branch of the facial nerve : Section of this nerve would result in paralysis of the muscles of the corner of the mouth: drooling would occur .

74. Facial nerve injury in babies: As the mastoid process is rudimentary(not completely developed) at birth, the facial nerve is more easily damaged in babies. Birth injuries or other trauma, can therefore cause an ipsilateral facial palsy. This is serious since buccinator, supplied by VII, is necessary for sucking(feeding). CLINICAL NOTES 75

75. Acoustic neuroma : This is a tumour of Schwann cells on the vestibular nerve in the IAM(Internal Acoustic Meatus). Since the tumour grows within a bony canal it may compress the facial and vestibulocochlear nerves causing a particular type of deafness (nerve deafness) and an ipsilateral facial 84 palsy. CLINICAL NOTES

76. Cerebellopontine angle tumours : Tumours in this region would cause signs and symptoms of damage to the facial and vestibulocochlear nerves and cerebellar signs. These include facial palsy, deafness, vertigo and poor coordination . CLINICAL NOTES 77

77. Evaluation of Nerve function 78 HISTORY is of vital importance to establish the onset characteristics, duration and degree of recovery. Previous trauma, surgery or infection may help in arriving at a diagnosis Examination of the face at rest and movement. Radiologic evaluations : CT, MRI Nerve function tests : topognostic testing, ear pain, taste, tearing, salivation, stapeus reflex/auditory testing, vestibular testing, electronystagmography, Electrophysiologic testing: Evoked electromyography.

78. CONCLUSION 79 The most important thing about the intracranial course of Facial Nerve is its relationship to the middle ear. The most important thing about the extracranial course is its relationship to the parotid gland. Hence a complete understanding of its anatomy is essential and care should be taken during surgical procedures.

79. RE F ER E NCES 80 Gray’s anatomy 2 nd edition Head and neck anatomy- Berkovitz ; Moxham Essentials of human anatomy : 9 th edition. Russell T ; William B.D.Chaurasia’s Human Anatomy 4 th edition Clinical Anatomy 2 nd edition -Neeta V Kulkarni The Facial Nerve – May’s 2 nd edition e d ition Handbook of local anaesthesia- Stanley F Malamed 5 th Shafer’s Textbook of Oral Pathology -5 th edition Atlas of clinical gross anatomy- Kenneth , John , Pedro.

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