Facial Nerve Palsy - Facial Nerve Branches SAQ and Answers

Facial Nerve Palsy - Facial Nerve Branches  SAQ and Answers

2. A patient presented with deviation of the mouth to the left, inability to close the right   eye and inability to wrinkle the skin of the right side of the forehead. He had loss of taste   sensation on the right side of the tongue. Corneal reflex was absent on the right   side.  

2.1 State the most likely cranial nerve affected  (10 marks)
2.2 State the most likely site of the lesion giving reasons.   (20 marks)
2.3 Explain the anatomical basis for the above clinical findings.  (40 marks)
2.4 Draw a labelled line diagram to illustrate the pathway of the corneal reflex.     (30 marks) 

Answers :

2
2.1 Facial Nerve (CN VII) of right side.

2.2 In this patient both the upper and the lower part of the right half of the face is affected. Therefore, this this is an infranuclear (LMN) lesion, where both motor and sensory components of the nerve are involved. The main facial nerve and nervus intermedius emerge separately from the brain stem, pass laterally in the cerebellopontine angle into the internal acoustic meatus. Coursing through the petrous temporal bone they merge in to a single trunk in the facial canal. Afferent fibers carrying taste sensation travel in the chorda tympani nerve. This is a branch of the facial nerve given off in the facial canal, just before it exists through the stylomastoid foramen as a purely motor nerve. Thus the lesion is proximal to the origin of chorda tympani with in the facial canal.

2.3  Emerging from the stylomastoid foramen, the facial nerve enters the parotid gland. It forms a plexiform arrangement within the gland and emerge as five main groups of branches; temporal, zygomatic, buccal, marginal mandibular and cervical. The facial nerve thus supplies the ipsilateral muscles of facial expression. Temporal branches supply part of the frontalis muscle, paralysis of which results in the inability to wrinkle the forehead. Zygomatic branches supply orbicularis oculi muscle that closes the eyelid tightly. Paralysis of this muscle that closes  drooping of the eyelid and inability to close it tightly. Often leads to corneal ulceration. This also results in the absence of corneal reflex.

2.4. Touch on sclera-corneal junction – right
  Impulses are transmitted through ophthalmic division of the trigeminal nerve – right
 trigeminal ganglion – right
 Sensory nucleus of trigeminal nerve in pons – right
 Reticular formation
 Motor nucleus of facial nerve – right
 Motor fibers of facial nerve – right
 Zygomatic branch – right
 Orbicularis oculi muscle – right
 Closure of eyelid - right