facial nerve Anatomy phydiology and clinical aspects

Facial nerve is the seventh cranial nerve.Being a mixed type of nerve it has both motor and sensory component. Its clinical aspect are very important to discuss

1. Facial nerve (cranial nerve VII) Dr. Farzana sharmin ( jui )

2. Facial nerve cont.. The facial nerve is both motor & sensory nerve . It has three nuclei : 1) Main motor nucleus                              2) the parasympathetic nuclei                              3) the sensory nucleus .

3. Main motor nucleus : this lies within the pons. The part of the nucleus that  supplies the muscles of the upper  part of the face receives corticonuclear  fibers from the precentral gyri of both cerebral  hemispheres. The part of the nucleus that supplies the muscles of the lower part of the face receives corticonuclear fibers from the opposite cerebral hemisphere.

4. Parasympathetic nuclei : these lie posterolateral to the main motor nucleus. They are the sup. Salivatory & lacrimal nuclei   Sup. Salivatory nucleus-   supplies secretomotor fibers to the  submandibular & sublingual salivary glands. Test sensation from the nucleus of the solitary tract from the mouth cavity

5.   The lacrimal nucleus -   supplies secretomotor  fibers to the lacrimal   gland. It receives afferent fibers from the hypothalamus for emotional responses & from the sensory nuclei of the trigeminal nerve  for reflex lacrimation 2ndary to irritation of the cornea or conjunctiva.

6. Lacrimatory nucleus (pons) Nervus intermedius(sensory root of facial nerve) Geniculate ganglion of facial nerve (no relay) Greater superficial petrosal nerve + Deep petrosal nerve (sympathetic)

7. Nerve of pterygoid canal ( vidian nerve) Sphenopalatine ganglion (preganglionic parasympathetic fibers relay here) Zygomatic nerve(postganglionic fibers) Zygomaticofacial branch Lacrimal nerve Lacrimal Gland

8. Sensory nucleus : this is the upper part of the nucleus of the tractus solitarius & lies close to the  motor nucleus. Sensation of taste travel from the ant. Two thirds of the tongue & from the floor of the mouth & plate. The sensations travel through the perepheral axons of nerve cells in the geniculate ganglion on the 7th cr. Nerve . 

9. Sensory nucleus cont..   The efferent fibers cross the midline & ascend to the   thalamus where they are relayed to the taste area of the   cerebral cortex in the lower part of the post central gyrus  

10. Course & Distribution of the facial nerve

11. Terminal branches within the parotid gland

12. Blinking Reflex Blinking refers to a co-ordinated opening & closing movement of the eye lids. Blinking can be subdivided into 1)Voluntary blinking 2)Involuntary blinking: I) Spontaneous blinking II) Reflex blinking

13. Closing movement: Area IV (cerebral cortex) Facial Nerve (Pons) Pyramidal Tract Opening movement: Area VIII (frontal eye field area) Internal capsule 3 rd nerve nucleus (midbrain) Oculomotor nerve

14. Voluntary blinking: It is generally uniocular & used to illustrate a variety of emotions. It is under the control of the individual. Spontaneous blinking: it occurs without any obvious external stimulus or voluntary willed efforts. it occurs 1 in every 5 sec. & last for 0.3 sec. It is absent in neonates. It does not require retinal stimulation. It is also present in blind people.

15. Reflex Blinking : It refers to the co- ordinated closing & opening movements of the eyelids , which occur reflexly in response to some direct stimulus. It is subdivided into i ) Tactile reflex blinking ii)Optic reflex blinking iii)Auditory reflex blinking iv) Stretch reflex blinking

16. Tactile reflex blinking : Excited by a sudden unexpected touch to cornea, conjunctiva, eyelash, eyebrow, eyelids. Afferent pathway through 5 th cranial nerve & efferent pathway through 7 th cranial nerve. Auditory reflex blinking : It is excited by loud noise. Here afferent pathway through 8 th cranial nerve & efferent through facial nerve .

17. Optic reflex blinking : It includes dazzle reflex produced by shinning a bright light into the eye & the menace reflex, produced by an unexpected or threatening object coming suddenly in the near field of vision. Afferent pathway through optic nerve & the association fibres to the facial nucleus from the efferent path. Stretch type stimulus reflex blinking: This type of reflex blinking occurs when one orbicularis is stimulated by a stretch type stimulus such as a tap or blow

18. Upper motor nuron lesion   upper motor neuron lesion: Unable to smile Unable to whistle Loss of nasolabial fold Can raise both eyebrows

19.   Lower motor neuron lesion:  Drooping of corner of mouth Loss of nasolabial fold Can't raise the eyebrow on  affected side.

20. Evaluation  of a patient with 7th Cr. Nerve palsy Inspection: There is a gross facial asymmetry due to  Forehead wrinkling absent on affected side,  Widening of the palpebral fissure height of affected side Obliteration of nasolabial fold, Deviation angle of mouth to the affected side Rate of blinking decrease in affected eye.

21.  On palpation pt wrinkling his forehead pt to close his eyes Blow out your cheeks & closing mouth pt to show his teeth pt to whistle.

22. Examination : To inflate his mouth- tap with the fingure on eye inflected chick compare two chicks strength, Compare fine touch in both side starting from forehead to cheek both side 5th nerve test

23. Examination cont.. Corneal sensation for V nerve Hyperacusis test – compare the sound on both ear Taste sensation- sweet, salt, sour, bitter Schirmer's test for dry eye Pupillary reaction for 3rd nerve & ocular motility Slit lamp examination to see exposure keratopathy

24.   Causes of facial nerve palsy: Idiopathic Viral herpes zoster virus mainly Traumatic medical cause such as DM, HTN, Acoustic neuroma Diseases of brain stem

25. Applied Aspects In supranuclear lesions of the facial nerve: Only lower part of the controlateral face is paralysed . The upper part escapes due to bilateral representation in the cerebral cortex. Cause- cerebrovascular accidents & tumours

26.    Infranuclear lesions of the facial nerve: Whole of the face of the ipsilateral side is paralysed , abolishing both voluntary & emotional movements. Face become asymmetrical & drawn up to the normal side .

27. Affected side become motionless Wrinkles disappear from the forehead Lagophthalmos present Any attempt to smile draws the mouth to the normal side.

28. During mastication, food accumulates of labialis is impaired Common cause: bell's palsy                            Diseases of the brainstem                            Acoustic neuromas                      

29. Lesions found distal to the choroda tympani : Produce isolated facial palsy Lesions proximal to the geniculate ganglia - loss of taste sensation on  ant. 2/3 rd   of the tongue & diminished salaivation

30.   Treatment of facial nerve palsy : A. specific treatment-   Systemic steroid- oral prednisolone  40-60mg/kg body weight for 1 week  If treatment started within 72 hours, rapid recovery occurs.

31.  Lesion proximal to the nerve to stapidius : Additional complaint of ipsilateral hyperacusis.  Ramsay- hunt syndrome: Due to herpes zoster infection of geniculate ganglion of the facial nerve, characterized by LMN type of facial palsy associated with severe pain in the ear & vesicles .

32. Treatment Supportive treatment-  Artificial tear ointment Physiotherapy  Temporary  tarsotherapy Spontaneous recovery in 80% cases within 12 weeks

33.  Lesions at the level of pons:  Involvement of both 6th cr. Nerve & 7th cr. Nerve  Lesions at the cerebellopontine angle: Involvement of both 7th cr. Nerve & auditory nerve.

34. Paralytic ectropion/ facial nerve palsy Caused by ipsilateral facial nerve palsy Association with retraction of the upper & lower lids &brow ptosis. The latter may mimic narrowing of palpebral aperture Complications: Exposure keratopathy –due to lagophthalmos Watering- caused by malposition of the inferior lacrimal punctum, failure of lacrimal pump mechanism Increasing tear production resulting from corneal exposure.

35. Treatment Temporary measures – to protect the cornea Lubrication with high viscosity tear substitutes , & ointment , taping shut of the lids during sleep - usually adequate in mild case. Botulinum toxin injection into the levator to induce temporary ptosis. Temporary tarsorrhaphy may be necessary , particularly pt with poor Bell phenomenon, where the cornea remains exposed when the pt attempts to blink. The lateral aspects of the upper & lower lids are sutured together.

36. Permanent : irreversible damage to the facial nerve which may occur following removal of acoustic neuroma, or when no further improvement has occurred for 6-12 months in a bell’s palsy. Medial canthoplasty Lateral canthal sling or tarsal strip Upper eyelid lowering by levator disinsertion Pt with lagophthalmos either gold or platinum weights can be implanted in to the upper eyelid A small lateral tarsorrhaphy

37. Mobius syndrome is a rare, usually sporadic condition, basic components of which are rare congenital non progressive bilat. 6 th & 7 th Cr palsies Nerve That are relate to a developmental abnormality of the brainstem

38. Mobius syndrome continue.. Systemic features Bilateral facial palsy , which is usually asymmetrical & often incomplete, giving rise to an expressionless facial appearance problem with eyelid closure . 5 th , 8 th , 10 th , 12 th Cranial nerve may also be affected Limb anomalies & mild mental handicap may be present.

39. Ocular features: Bilat. 6 th nerve palsy. Horizontal gaze palsy (50%) Occasionally ,3 rd & 4 th palsy & ptosis.