Anatomy & Histology · patient case question
Which muscle group is responsible for the failure to purse the lips and retain fluid?
Patient case: Unilateral Facial Weakness
demo: 49-year-old male
chief: “I woke up and the right side of my face was drooping.”
history: Recent upper respiratory infection. No prior neurologic events.
meds: None
findings: Drooping of the right corner of the mouth with inability to purse the lips or retain fluid. Forehead wrinkling and eye closure are preserved on the affected side. No sensory deficit. Nerve pathway illustrated below.
Show answer and explanation
Correct answer: C. Orbicularis oris
- A. Masseter is a muscle of mastication supplied by the mandibular division of the trigeminal nerve; it elevates the mandible.
- B. Mylohyoid forms the floor of the mouth and is supplied by the nerve to mylohyoid, a trigeminal branch.
- C. Correct. Orbicularis oris is the sphincter of the mouth, a muscle of facial expression innervated by the facial nerve. Its paralysis produces oral incompetence and drooling.
- D. The medial pterygoid is likewise trigeminal and involved in mandibular movement, not lip seal.
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