Facial nerve

facial nerve is the 7th cranial nerve. it supplies the parts of the face and also the muscles of mastication. it helps in the expression of the face too.

1. PRESENTED BY- Dr. Alvi Fatima JR I Department of Pedodontics FACIAL NERVE 1

2. CONTENTS Introduction Embryology of facial nerve Nuclei of facial nerve Functional components Course- Intracranial course Extracranial course Branches of Facial nerve Terminal branches Ganglia’s associated with facial nerve Vascular supply Applied anatomy 2

3. INTRODUCTION Seventh cranial nerve Nerve of second branchial arch It is a mixed nerve carrying both sensory & motor fibres 3

4. EMBRYOLOGY The facial nerve is developmentally derived from the hyoid arch, which is the second branchial arch 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 4

5. 5 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

6. 3 rd week- Facioacoustic primordium - Rhombencephalon 4th week- Development of first branch- rostral end of embryo 6

7. Early 5th week, the geniculate ganglion forms from distal part of primordium It separates into 2 branches : main trunk of facial nerve and chorda tympani 7

8. 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 8

9. Towards the seventh week the tympanic cord will be derived from the first branch of the facial nerve, joining elements of the first branchial arch and the lingual nerve. By the middle of this week, the trunk of the facial nerve, which is already formed, bifurcates into the temporofacial and cervicofacial branches. Around the end of this week different fascicles that originate from these branches are recognized clearly. The temporal, zygomatic , oral, mandibular and cervical regions will give origin to the five main (terminal branches) of the facial nerve. 9

10. Towards the end of pregnancy, the tympanic bone and the mastoid process are not fully developed, so the petrous portion of the facial nerve does not exist and will not be formed until between 2 and 4 years of age. 10

11. NUCLEI OF FACIAL NERVE 11

12. MOTOR NUCLEUS OF FACIAL NERVE- It lies in the lower part of pons below. The fibres supplying the muscles of second branchial arch originate from here . SUPERIOR SALIVATORY NUCLEUS- It lies in the pons, lateral to the motor nucleus. It provides preganglionic parasympathetic sectretomotor fibres 12

13. NUCLEUS OF TRACTUS SOLITARIUS- It receives the fibres that are responsible for taste sensation SPINAL NUCLES OF TRIGEMINAL NERVE- It lies in the medulla & receives fibres for pain & temperature sensations from external auditory meatus 13

14. 14 receives fibres for pain & temperature sensations from external auditory meatus are responsible for taste sensation The fibres supplying the muscles of second branchial arch originate from here. It provides preganglionic parasympathetic sectretomotor fibres

15. FUNCTIONAL COMPONENTS 15

16. GENERAL VISCERAL EFFERENT- These fibres arise from cell bodies of superior salivatory nucleus in medulla. Axons pass peripherally to synapse in submandiblar pterygopalatine ganglion. It provides secretomotor fibres to- Submandibular gland Sublingual gland Lacrimal gland Mucous glands of nose, palate & pharynx Auditory tube Paranasal air sinses 16

17. 2. SPECIAL VISCERAL EFFERENT- It originates from the cell bodies of facial motor nucleus within the pons. Axons pass peripherally to supply muscles derived from second branchial arch which includes muscles of facial expressions, platysma , stylohyoid muscle, posterior belly of digastrics muscle, stapedius muscle. 17

18. 3. SPECIAL VISCERAL AFFERENT- It originates from cell bodies within geniculate ganglion. Central fibres pass back to the brainstem to synapse in the nucleus of soliatary tract of medulla. Peripheral fibres carries taste sensations from anterior two-third of tongue & palate, except circumvallate papillae. 18

19. 4. GENEREAL SOMATIC AFFERENT- These fibres arise as a small component from cell bodies in the geniculate ganglion of facial nerve. Central fibres pass back to brainstem to synapse within the principal sensory nucleus of trigeminal nerve. It sends proprioceptive impulses from the muscles of facial expressions & sensations from external auditory meatus 19

20. FUNCTIONAL COMPONENT NUCLEI ASSOCIATED SUPPLY General visceral efferent Superior salivatory nucleus Submandibular gland Sublingual gland Lacrimal gland Paranasal air sinuses Auditory tube Mucous gland of nose, palate & pharynx Special visceral efferent Motor nucleus in Pons Muscles of facial expression Posterior belly of diagastric Platysma Stapedius muscle 20

21. FUNCTIONAL COMPONENTS NUCLEI ASSOCIATED SUPPLY Special visceral afferent Nucleus of tractus solitarius in medulla Carries taste sensations from anterior two-third of tongue & palate except vallate papillae General somatic afferent Spinal nucleus of trigeminal nerve Sends proprioceptive impulses from muscles of facial expression & external auditory meatus 21

22. INTRACRANIAL COURSE 22

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26. After arising from brainstem, the two roots pass forwards & laterally along with eighth nerve & enter the internal acoustic meatus located on the posterior surface of the petrous temporal bone. They run through the meatus laterally & combine at its lower end to form a single trunk. 26

27. The nerve then enters the facial canal in petrous temporal bone & runs for a short distance laterally above the vestibule of the inner ear. As it reaches the medial wall in the epitympanic part of middle ear, it turns sharply backwards making an acute bend called the genu or knee of facial nerve. 27

28. The nerve presents with a ganglion on this bend known as the geniculate ganglion. The nerve now runs horizontally backwards in a bony canal above the promontory producing a bulge in the medial wall of middle ear. 28

29. On reaching the junction between the medial & the posterior walls of middle ear, the nerve turns downwards & continues vertically in facial canal & drops inferiorly to exit through the stylomastoid foramen at the base of the skull. 29

30. EXTRACRANIAL COURSE Facial nerve curves around lateral aspect of styloid process & enters posteromedial aspect of parotid gland. It gives terminal branches behind the neck of mandible which arises from the anteromedial surface 30

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32. It arises from the genu of facial nerve within the facial canal. The nerve passes anteriorly & medially through bone & exits through the superior hiatus on the anterior slope of petrous temporal ridge in the middle cranial fossa. GREATER PETROSAL NERVE 32

33. Here it heads towards the foramen lacerum , drops partially through, & then enters the pterygoid canal. At this point, it joins with deep petrosal nerve to form nerve to pterygoid canal . It travels through the canal & joins pterygopalatine ganglion . The nerve conveys preganglionic secretomotor fibres to lacrimal gland & nasal mucosa. 33

34. It arises in the facial canal behind the middle ear & runs forwards through a short canal to reach & supply stapedius muscle. NERVE TO STAPEDIUS 34

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36. CHORDA TYMPANI NERVE It arises in the facial canal about 6mm above the stylomastoid foramen & enters the middle ear . It passes forwards across the inner surface of tympanic membrane internal to handle of malleus & then leaves the middle ear by passing through petrotympanic fissure to appear at the base of the skull 36

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38. Then it joins the lingual nerve in the infratemporal region . Chorda tympani nerve carries- Taste fibres from anterior two-third of tongue except the circumvallate papillae . Secretomotor fibres to submandibular & Sublingual glands. 38

39. POSTERIOR AURICULAR NERVE It arises just below the stylomastoid foramen. It divides into two branches- Auricular branch which supplies the muscles of auricle Occipital branch which supplies the occipital belly of occipito-frontalis . 39

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41. NERVE TO POSTERIOR BELLY OF DIGASTRIC It arises near the origin of posterior auricular nerve & supplies the posterior belly of digastric. 41

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43. TERMINAL BRANCHES OF FACIAL NERVE ZYGOMATIC NERVE Runs across zygomatic bone to supply orbicularis oculi muscle BUCCAL NERVE Two branches. Upper branch runs above parotid duct & lower below to supply buccinator muscle 43

44. MARGINAL MANDIBULAR NERVE Runs below angle of mandible & crosses body of mandible to supply lower lip & chin CERVICAL NERVE Emerges from apex of parotid gland & runs downwards in neck to supply platysma & depressor anguli oris muscle 44

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47. GANGLIA ASSOCIATED WITH FACIAL NERVE 47

48. Geniculate Ganglion The geniculate ganglion (from Latin genu , for "knee") is an L-shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head. It receives fibers from the motor, sensory, and parasympathetic components of the facial nerve and sends fibers that will innervate the lacrimal glands, submandibular glands, sublingual glands, tongue, palate, pharynx, external auditory meatus , stapedius , posterior belly of the digastric muscle, stylohyoid muscle, and muscles of facial expression. 48

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50. Submandibular Ganglion This is a perioheral ganglion Its relay station for secretomotor fibers to the submandibular and sublingial glands Topographically it is related to lingual branch And functionally to chorda tympani 50

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52. Pterygopalatine Ganglion The pterygopalatine ganglion ( meckel's ganglion, nasal ganglion or sphenopalatine ganglion) is a 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 52

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54. Facial Nerve blood supply 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 54

55. Stylomastoid artery (branch of posterior auricular artery) – mastoid segment Posterior auricular artery supplies the facial nerve at & distal to stylomastoid foramen Venous drainage parallels the arterial blood supply 55

56. AGE CHANGES CHILD ADULT Chorda tympani may exit through Stylomastoid Foramen Chorda tympani exit proximal to Stylomastoid Foramen 2nd genu is more acute and lateral 2nd genu is less acute and medial Nerve trunk is more anterior and lateral on exit through Stylomastoid Foramen Nerve trunk is less anterior and deeper Nerve very superficial over angle of mandible Nerve less superficial over angle of mandible 56

57. EXAMINATION OF FACIAL NERVE Inspect the face for asymmetry Ask patient to shut both eyes & compare strength of closure on each side Ask the patient to look up & see for loss of wrinkling Observe the patient for frowning & puffing of cheeks 57

58. CLINICAL & APPLIED ANATOMY 58

59. Dysfunction of facial nerve can be due to disorders of under activity or over activity . it can be further localized anatomically to supranuclear , nuclear & infranuclear lesions. 59

60. It can be of two types- UPPER MOTOR NEURON FACIAL PARALYSIS LOWER MOTOR NEURON PALSY 60

61. UPPER MOTOR NEURON FACIAL PARALYSIS- It is due to involvement of cortico -nuclear fibres . These fibres arise in the cerebral cortex, pass through internal capsule & end in the motor nucleus of facial nerve. Since the lesion is above the nucleus, it is called as supranuclear facial palsy 61

62. It leads to paralysis of contralateral lower part of face below the palpeberal fissure The upper part of the face is speared because the part of facial nucleus which supplies It is innervated by cotico nuclear fibres from both the cerebral hemispheres 62

63. LOWER MOTOR NEURON PALSY It is of two types Nuclear paralysis- It is due to involvement of the nucleus of facial nerve. This can occur due to poliomyelitis or lesion of the pons. The motor nucleus of facial nerve is close to the abducent nerve which is also usually affected. Paralysis of muscles of the entire face on ipsilatereal side occurs. 63

64. Infranuclear paralysis- This occurs due to involvement of facial nerve. 64

65. DISORDERS OF UNDERACTIVITY DISORDERS OF UNDERACTIVITY 65

66. BELL’S PALSY Bell’s palsy is named after Sir Charles Bell who first described the syndrome Incidence- 11-40 per 100,000 persons Common in the age of 40’s Common in diabetic patients & pregnant women 66

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68. CLINICAL FEATURES Weakness or complete paralysis of all muscles on one side of face Forehead unfurrows, loss of nasolabial fold, drooping of corner of mouth Bell’s phenomenon- The eyelids do not close but on attempted closure, the eye rolls upwards. Decreased tear production & eye irritation When patient smiles, face becomes distorted & deviated to side opposite to the palsy posterior auricular pain 68

69. ETIOLOGY Idiopathic- It is caused by inflammation of facial nerve at the geniculate ganglion which leads to compression & ischaemia . But the cause of inflammatory process remains uncertain HERPES SIMPLEX VIRUS INFECTION- HSV-1 titres are found to be higher in affected patients. After causing the primary infection, the virus resides in the geniculate ganglion. At the time of stress, the virus reactivates & causes local damage to myelin 69

70. LYME DISEASE- History of tick exposure, rash or athralgias is found RAMSAY HUNT SYNDROME- It is characterized by pronounced prodrome of pain & development of vesicular eruptions in the ear canal & pharynx . OTITIS MEDIA— infection of medial ear 70

71. DIAGNOSIS OCULAE EXAMINATION- Patient is unable to completely close his eye on the affected side ORAL EXAMINATION- Taste & salivation is affected 71

72. (Ref- Aris Garro , Lise E Nigrovic - Managing Peripheral Facial Palsy- Annals of Emergency Medicine- May 2018- vol-71, issue- 5, pg no- 618-624) 72

73. RAMSAY HUNT SYNDROME Triad of facial paralysis, herpetiform vesicular eruptions & vestibulocochlear dysfunction PATHOGENESIS- Reactivation of latent varicella zoster virus in geniculate ganglion of facial nerve 73

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75. LYME DISEASE It is a kind of facial paralysis caused with infection with Borrelia burgdorferi via tick bites It affects skin, nervous system, musculoskeletal system. TREATMENT- Doxycycline - 100mg bid Amoxycillin - 500mg tid Cefuroxime - 500mg bid (Ref- GrazynA Biesiada - Lyme disease- a review- Archives of Medical Science- October 8, 2012, pg no- 978-982) 75