This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuroanatomy, Subject name: Anatomy
[{'content': 'Trismus is due to spasm of which muscle? \nSelect and explain. \nA. Orbiculis, B. Lateral pterygoid, C. Mentalis, D. Medial pterygoid', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. D Medial pterygoidRef: Gray's Anatomy 41st ed. P 552* Trismus/Lock jaw is painful reflex muscle spasm. It occurs due to spasm of muscle of mastication and leads to inability to open the oral cavity* Trismus occurs due to involvement of masseter or medial pterygoid muscle or due to sub mucosal fibrosis.* Note: Infection of pterygomandibular region can cause trismus, which usually affects medial pterygoid muscle.", 'role': 'assistant'}]