Facial nerve234


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antomy of facial nerve and its clinical importance

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Facial nerve234

  1. 1. FACIAL NERVE Dr Shermil sayd
  2. 2. Introduction  Seventh cranial nerve  Nerve of the second branchial arch  Motor nerve supply of the face
  3. 3. Surface marking It is marked by a short horizontal line which joins the following two points  A point at the middle of the anterior border of the mastoid process. The stylomastoid foramen lies 2cm deep to this point  A second point behind the neck of the mandible. Here the nerve divides into its five branches
  4. 4. Functional Components 1. Special visceral or branchial efferent-for muscles responsible for facial expression and for elevation of the hyoid bone 2. General visceral efferent or parasympathetic- they are secretomotor to the submandibular and sublingual salivary glands, lacrimal glands & glands of the nose. 3. General visceral afferent- carries afferent impulses from the above mentioned glands 4. Special visceral afferent fibres- carry taste sensations from the anterior two third of the tongue, except from vallate papillae & from the palate
  5. 5. 5. General somatic afferent- probably innervate a part of the skin of the ear. This nerve doesn’t give any direct branches to the ear. But may reach it through the communication with the vagus nerve.
  6. 6. Nuclei  The four nuclei are presented in the lower pons 1. motor nucleus or the branchiomotor 2. superior salivary nucleus or parasympathetic 3. lacrimatory nucleus is also parasympathetic 4. nucleus of the tractus solitarius which is gustatory and receives afferent fibres from the glands
  7. 7.  Motor nucleus lies deep in the reticular formation of the lower pons  The part of the nucleus that supplies the muscles of the upper part of the face receives corticonuclear fibres from the motor cortex of the both left and right sides.  The part of the nucleus that supplies muscles of the lower part of the face receive corticonuclear fibres only from the opposite cerebral hemisphere
  8. 8. Course and relations (intracranial)  Attaches to the brain stem by two roots, motor & sensory (nervus intermedius)  Attached to the lateral part of the lower border of the pons just medial to the eighth cranial nerve  Two roots run laterally forward to reach the internal acoustic meatus  In the meatus, motor root lies in a groove on the 8th nerve, with sensory root intervening & accompanied by the labyrinthine vessels
  9. 9.  At bottom or fundus of the root , sensory and motor join to form a single nerve trunk which lies in the petrous temporal bone  Within the canal the nerve course is divided in 3 parts by two bends 1. Directed laterally above the vestibule 2. Runs backwards and in relation to the medial wall of the middle ear, above the promontory 3. Vertically downwards behind the promontory
  10. 10.  1st bend at the junction of 1st and 2nd part is sharp, lies over the anterosuperior part of the promontory, Also called as the genu.  it is called so because it lies on the genu  2nd bend is gradual and lies between the promontory and the aditum to the mastoid antrum  Leaves the skull through the stylomastoid foramen
  11. 11. Course and relations (extracranial)  Facial nerve crosses the lateral side of the base of the styloid process  It enters the posteromedial surface of the parotid gland, runs forwards through the gland crossing the retromandibular vein and the ECA.  Behind the neck of the mandible, it divides into 5 terminal branches which emerge along the anterior border of the parotid gland
  12. 12. Branches and distribution Within the facial canal 1. Greater petrosal nerve 2. Nerve to the stapedius 3. Chorda tympani As it exits from the stylomastoid foramen 1. Posterior auricular 2. Digastric 3. Stylohyoid
  13. 13.  Terminal branches within the parotid gland 1. Temporal 2. Zygomatic 3. Buccal 4. Marginal Mandibular 5. Cervical  Communicating branches with the adjacent cranial and spinal nerves
  14. 14. Greater petrosal nerve  Carries gustatory and parasympathetic fibres  Arises from the geniculate ganglion of the facial nerve, 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 fibres to form the nerve of the pterygoid canal
  15. 15. Nerve to the stapedius  Arises opposite the pyramid of the middle ear, and supplies the stapedius muscle  Damps excessive vibrations of the stapes caused by high pitched sounds.  In paralysis, it causes hyperacusis
  16. 16. Chorda tympani nerves  Arises in the vertical part of the facial canal about 6mm above the stylomastoid foramen  Runs upwards and forwards in a bony canal  Enters the middle ear and runs forwards in close relation to the tympanic membrane  Leaves the middle ear by passing through the petrotympanic fissure  It then passes medial to the spine of the sphenoid and enters the infratemporal fossa.  Joins the lingual nerve through which it is distributed
  17. 17. Carries 1. Preganglionic secretomotor fibres to the submandibular ganglion for supply of the submandibular and sublingual salivary glands 2. Taste fibres from the anterior two thirds of the tongue
  18. 18. Posterior auricular nerve  Arises just below the stylomastoid foramen  Ascends between the mastoid process and the external acoustic meatus and supplies 1. The auricularis posterior 2. The occipitalis 3. The intrinsic muscles on the back of the auricle
  19. 19. Digastric branch  Arises close to the previous nerve  It is short and supplies the posterior belly of the digastric
  20. 20. Stylohyoid branch  Arise with the digastric branch  Its long and supplies the stylohyoid muscle
  21. 21. Temporal branches  Crosses the zygomatic branch – auricularis anterior – Auricularis superior – Intrinsic muscles on the lateral side of the ear – Frontalis – The orbicularis occuli – Corrugator supercili
  22. 22. Zygomatic branch  Runs across the zygomatic bone and supply the orbicularis occuli
  23. 23. Buccal branches  Two branches 1. Upper- runs above the parotid duct 2. Lower- runs below the duct They supply the muscles in the vicinity, i.e. muscles of the cheek and upper lip
  24. 24. Marginal mandibular branch  Runs below the angle of the mandible deep into the platysma  Crosses the body of the mandible and supplies muscles of the lower lip and the chin
  25. 25. Cervical branch  Emerges from the apex of the parotid gland  Runs downwards and forwards in the neck to supply the platysma
  26. 26. Communicating branches  For effective coordination between the movements of the muscles of the 1st , 2nd and 3rd branchial arches, the motor nerves of the 3 arches communicate with each other  Also communicates with the sensory nerves distributed over its motor territory
  27. 27. Ganglia Three ganglions 1. The geniculate ganglion is situated on the 1st bend of the facial nerve, in relation to the medial wall of the middle ear. A sensory ganglion. Taste fibers present are peripheral processes of pseudounipolar neurons present in the geniculate ganglion 2. Submandibular ganglion -parasympathetic ganglion for relay of secretomotor fibres to the submandibular and sublingual glands 3. Pterygopalatine ganglion is also a parasympathetic ganglion
  28. 28. Clinical anatomy
  29. 29. Facial nerve paralysis  Facial nerve paralysis is the most common complication in dental practice  Paralysis of some of its branches occur whenever an infraorbital block/max. canine infiltration given  Muscle droop is observed when the LA solution is deposited in the deep lobe of the parotid gland, through which terminal portions of the facial nerve extends, which is a transient condition  Duration depends upon the duration of action of the LA solution injected
  30. 30.  Patient has unilateral facial muscle paralysis & be unable to use these muscles  Face appears lopsided  No treatment other than waiting until the action of the drug resolves  Patient is unable to voluntarily close one eye  Protective lid reflex of one eye is abolished, but the corneal reflex is normal
  31. 31. Bell’s palsy  Facial weakness  Evidence for herpes simplex type 1 infection causing infranuclear lesions  Paralysis: Progresses to maximal deficit over 3 to 72 hours  Pain (50%): Near mastoid process  Hyperacusis  Facial weakness  Sensory loss is Mild or None
  32. 32.  Food accumulates between the teeth and cheek  Labial articulation is impaired
  33. 33. Supra nuclear lesion  Its usually a part of the hemiplegia  Only the lower part of the opposite side of the face is paralysed  The upper part with the frontalis and orbicularis occuli escapes due to its bilateral representation in the cerebral cortex
  34. 34. VII disorders Unilateral nerve paralysis – Leprosy – Lyme disease – Neoplasm and masses – Trauma – Cardiofacial syndrome
  35. 35. VII disorders Bilateral nerve paralysis 1. Melkersson syndrome 2. Möbius syndrome & Congenital facial paresis 3. Guillain barre disease 4. Leprosy 5. HIV infection 6. Myasthenia gravis
  36. 36. Parotid gland relation  During the removal of parotid gland, the facial nerve is preserved by removing the glands in two parts, superficial and deep separately.  The plane of cleavage is defined by tracing the nerve from behind, forwards  Mixed parotid tumour is a slowly growing parotid tumour which doesn’t involve the facial nerve, but when it turns malignant, it then involve the facial nerve
  37. 37. TMJ relation  Temporal branches of the facial nerve is related to the lateral aspect of the TMJ  This leads to invariable damage to the facial nerve during surgical correction of TMJ ankylosis  This can mostly avoided by taking strict care during the preocedure  Indian Journal of Dental Research. 2013 Jul-Aug;
  38. 38. Conclusion Facial nerve is a nerve which is mostly motor in function, but also plays a small role in taste sensation. Its motor function is for the muscles of facial expression, which is important for a good quality of life. So every care should be taken to preserve these nerves, whatever the case may be.
  39. 39. References  Oral and maxillofacial surgery-Daniel M laskin  Local anesthesia- malamed  Differential diagnosis of oral and maxillofacial lesions-wood goaz  Contemporary oral and maxillofacial surgery-peterson  Human anatomy-chaurasia  Indian Journal of Dental Research. 2013 Jul-Aug;  Melkersson-Rosenthal syndrome and orofacial granulomatosis- Dermatol Clin. 1996 Apr;14(2):371-9.  Bell palsy in lyme disease-endemic regions of canada: a cautionary case of occult bilateral peripheral facial nerve palsy due to Lyme disease-CJEM. 2012 Sep;14(5):321-4.  Clinical spectrum of peripheral facial paralysis in HIV-infected patients according to HIV status-int J STD AIDS. 2013 Mar 6.
  40. 40. Thank You