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Injury to the lower division of the facial nerve during parotid surgery
will result in
A. inability to furrow the brow (to frown) on the same side
B. numbness over the angle and mental region of the jaw on the same side
C. ptosis of the eye on the same side
D. weakness in closing the eye on the same side
E. weakness of the lower lip on the same side
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hello maryam need your help..
Do you have nbme form 7? i just did it, got bad score 205. my exam is in 24th..
please help..
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The correct answer is E.
The motor component (special visceral efferent) of the facial nerve (CN VII) exits the skull via the stylomastoid foramen, passes lateral to the styloid process, and then enters the parotid gland. Within the gland, two divisions can usually be identified (upper and lower), that in turn give off five named branches that innervate the muscles of the face. The upper division gives rise to the temporal and zygomatic branches, which collectively innervate the frontalis, corrugator, and orbicularis oculi muscles. The lower division gives off the buccal, mandibular, and cervical branches. The largest, the buccal, innervates the muscles attaching to the upper lip, including the orbicularis oris and the levators, as well as the buccinator and the muscles of the nose. The mandibular branches innervate the muscles of the lower lip and of the chin, while the cervical branch innervates the platysma muscle. It should be noted that there are usually communicating branches between the named terminal nerves so that overlapping innervation of the muscles occurs. If the lower division is injured, there will be weakness (not frank paralysis because of the innervation overlap) of the muscles that attach to the lower lip.
An inability to furrow the brow (choice A) would be caused be denervation of the corrugator supercilii and frontalis muscles, which are innervated by the upper division of the facial nerve.
Choice B is wrong because once the facial nerve emerges from the stylomastoid foramen, it is a pure motor nerve (special visceral efferent, or branchiomotor nerve). It carries no sensory nerve fibers.
Ptosis (a drooping of the upper eyelid; choice C) is the result of a paralysis of the levator palpebrae muscle, which is innervated by the oculomotor (CN III) nerve.
Choice D is not correct because the orbicularis oculi muscle is innervated by branches from the upper division of the facial nerve.
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awesome question, Maryam. Thank you
