FACIAL NERVE its course and applied anatomy

Facial nerve

1. Facial nerve

2. Facial nerve

3. Contents Introduction Functional components Nuclei of facial nerve Ganglia Course and relation Branches and distribution Applied anatomy Conclusion

4. Introduction It is the 7 cranial nerve. It is the nerve of 2 brachial arch or hyoid arch It emerges from the pons of the brainstem Controls the muscles of facial expression Conveys taste sensations from the anterior 2/3 of the tongue

5. Functional components - Special visceral or branchial efferent(SVE), to muscles responsible for facial expression and for elevation of the hyoid bone. General visceral or efferent(GVE) or parasympathetic. These fibers are secretomotor to the submandibular and sublingual salivary glands, the lacrimal gland, and glands of the nose, the palate and the pharynx. General visceral afferent(GVA) component carries afferent impulses from the above mentioned glands. Special visceral afferent(SVA) carry taste sensations from the palate and from anterior two thirds of the tongue except from vallate papillae.

6. General somatic afferent(GSA) fibers probably innervate a part of the skin of the ear. The nerve doesn’t give any direct branches to the ear, but some fibers may reach it through communication with the vagus nerve.

7. Nuclei of facial nerve - The fibers of the nerve are connected to the four nuclei situated in the lower pons. 1. Motor nucleus or branchiomotor 2. Superior salivatory nucleus or parasympathetic 3. Lacrimatory nucleus is also parasympathetic 4. Nucleus of the tractus solitarius which is gustatory It also receives afferent fibers from the glands.

8. The motor nucleus lies deep in the reticular formation of the lower pons. The part of the nucleus that supplies muscles of the upper part of the face receives corticonuclear fibers from the motor cortex of both the right and left sides. In contrast, the part of the nucleus that supplies muscle of the lower part of the face receive corticonuclear fibers only from the opposite cerebral hemisphere.

9. GANGLIA The ganglia associated with the facial nerve are as follows – The 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.

10. The submandibular ganglion is a parasympathetic ganglion for relay of secretomotor fibers to the submandibular & sublingual glands. The preganglionic fibers come from the chorda tympani nerve.

11. The pterygopalatine ganglion is also a parasympathetic ganglion . Secretomotor fibers meant for the lacrimal gland relay in the ganglion.

12. Course and relation - The facial nerve is attached to the brainstem by two roots, motor and sensory. The sensory root is also called the nervus intermedius. The two roots of the facial nerve are attached to the lateral part of the lower border of the pons just medial to 8 th CN (vestibulocochlear). The two roots run laterally and forwards, with the 8th nerve to reach the Internal acoustic meatus.

13. In the meatus, the motor root lies in a groove on the 8th nerve, with the sensory root intervening. Here the 7th & 8th nerves are accompanied by the labyrinthine vessels . At the bottom or the fundus of meatus, the two roots sensory and motor, fuse to form a single trunk, which lies in the petrous temporal bone.

14. Within the canal, the course of the nerve can be divided into three parts by two bends. The first part is directed laterally above the vestibule; the second part runs backwards in relation to the medial part od the middle ear, above the promontory. The third part is directed vertically downwards behind the promontory.

15. The first bend at the junction of first and second part is sharp. It lies over the anterosuperior part of the promontory, and is called the genu. The geniculate ganglion of the nerve is so called because it lies on the genu. The second bend is gradual, & lies between the promontory and the aditus of the mastoid antrum.

16. The facial nerve leaves the skull by passing through the stylomastoid foramen.

17. In the extracranial course, the facial nerve crosses the lateral side of the base of the styloid process. It enters the posteromedial surface of the parotid gland, runs forward through the gland crossing the retromandibular vein and ECA. Behind the neck of the mandible, it divides into five terminal branches & emerge along the anterior border of the parotid gland.

18. Branches and distribution - 1) Within the facial canal: a) Greater petrosal nerve b) The nerve to the stapedius c) The chorda tympani 2) At its exit of stylomastoid foramen: a) Posterior auricular b) Digastric c) Stylohyoid 3) Terminal branches within the parotid gland: a) Temporal b) Zygomatic c) Buccal D) Marginal mandibular e) Cervical

19. GREATER PETROSAL NERVE relay Lacrimal gland

20. The nerve arises opposite to the pyramidal eminence. The  stapedius  is the smallest skeletal muscle in the body.  Is approximately 1 mm in length. Nerve to stapedius

21. Chorda tympani Arises in the vertical part of the facial canal about 6mm above the stylomastoid foramen. Runs upward and forward in bony canal. The chorda tympani exits the cranial cavity through the internal acoustic meatus along with the facial nerve. it travels through the  middle ear . It emerges from the skull into the infratemporal fossa. It soon joins the pathway of the larger  lingual nerve , a branch of the  mandibular nerve .

22. The fibers of the chorda tympani travel with the lingual nerve to the  submandibular ganglion . Here, the  preganglionic  fibers of the chorda tympani synapse with  postganglionic fibers  which go on to innervate the  submandibular  and  sublingual  salivary glands. Special sensory (taste) fibers also extend from the chorda tympani to the anterior 2/3 of the  tongue  via the lingual nerve.

23. Posterior auricular nerve Arises just below the stylomastoid foramen. It ascends between the mastoid process & the External acoustic meatus. It supplies – 1) auricularis posterior 2) occipitalis 3) intrinsic muscle of the back of the auricle.

24. Digastric branch It is short & supplies the posterior belly of digastric. Divides into several filament. One of these filaments joins the  glossopharyngeal nerve

25. Stylohyoid branch It arises from the digastric branch. Is long & supplies the stylohyoid muscle.

26. Terminal branches within the parotid gland- 1)TEMPORAL The terminal branches cross the zygomatic arch & supply – A) Auricularis anterior B) Auricularis superior C) Interinsic muscles on the lateral side of the ear D) Frontalis E) Orbicularis oculi F) Corrugator supercilii

27. Zygomatic branch Runs across the zygomatic bone. Supplies the orbicularis oculi.

28. Buccal branch They are two in number. The upper buccal branch runs above the parotid duct. The lower buccal branch runs below the duct. They supply the buccinator.

29. Marginal mandibular branch Runs below the angle of the mandible deep to the platysma. It crosses the body of the mandible and supplies muscles of the lower lip and chin.

30. Cervical branch It emerges from the apex of the parotid gland. Runs downwards and forwards in the neck to supply the platysma.

31. APPLIED ANATOMY

32. 1. Bell's palsy (Idiopathic facial nerve paralysis) It is a type of  facial paralysis  that results in an inability to control the  facial muscles  on the affected side. Symptoms include muscle twitching, weakness, or total loss of the ability to move one or rarely both sides of the face. Cause is unknown. Risk factors include  diabetes , a recent  upper respiratory tract infection , and  pregnancy . It results from a dysfunction of  7 th nerve.  can cause facial weakness include  brain tumor ,  stroke ,  Ramsay Hunt syndrome ,  myasthenia gravis , and  Lyme disease .

33. Bell's palsy is the most common cause of one-sided facial nerve paralysis (70%). It occurs in 1 to 4 per 10,000 people per year. About 1.5% of people are affected at some point in their life. It most commonly occurs in people between ages 15 and 60. Males and females are affected equally.

34. 2. Möbius syndrome extremely rare congenital neurological disorder which is characterized by  facial paralysis  and the inability to move the eyes from side to side. They cannot close their eyes or form facial expressions. Limb and chest wall abnormalities sometimes occur with the syndrome. 

35. 3. Melkersson –Rosenthal syndrome Melkersson –Rosenthal syndrome  is a rare  neurological disorder  characterized by recurring facial  paralysis . Swelling of the face and lips (usually the upper lip - cheilitis granulomatosis). The  development of folds and furrows in the tongue (fissured tongue) .

36. 4. Blepharospasm any abnormal contraction or twitch of the  eyelid . In most cases, blepharospasm symptoms last for a few days and then disappear without t/t, but in some cases the twitching is chronic and persistent, causing life-long challenges.

37. In these cases, the symptoms are often severe enough to result in functional blindness.  People have normal eyes, but for periods of time are effectively blind due to their inability to open their eyelids.

38. 5. Myokymia Myokymia is commonly used to describe an involuntary eyelid muscle contraction, typically involving the lower eyelid or less often the upper eyelid.  Since the condition typically resolves itself, medical professionals do not consider it to be serious or a cause for concern. In contrast, FACIAL MYOKYMIA is a fine rippling of muscles on one side of the face and may reflect an underlying tumor in the  brainstem ,  loss of myelin  in the brainstem, an inflammatory  polyneuropathy  that may affect the  facial nerve .

39. 6. Facial nerve paralysis in newborn The mastoid process is empty in newborn & stylomastoid foramen is superficial. Manipulation of baby’s head during delivery may damage the 7th nerve. This leads to paralysis of facial muscles especially the buccinator, for sucking milk.

40. 7. Crocodile tears syndrome Lacrimation due to abberant regeneration after trauma. Or in case of damage to facial nerve proximal to geniculate ganglion, regenerating fibers for submandibular salivary gland grow in endoneural sheaths of preganglionic secretomotor fibers supplying the lacrimal gland. This is why pt lacrimates while eating.

41. 8. Ramsay Hunt syndrome Is the reactivation of herpes zoster in the  geniculate ganglion . It shows following symptoms- Hyperacusis Loss of lacrimation Loss of sensation of taste in anterior 2/3 of tongue Bells palsy and lack of salivation Vesicles on the auricle.

42. Symptoms according to the level of injury to cranial nerve 7th