This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdomen and pelvis, Subject name: Anatomy
[{'content': 'Pudendal nerve supplying motor pa to external sphincter is derived from \nSelect and explain. \nA. L5 - S1 roots, B. S1 - S2 roots, C. L2 - L3 roots, D. S2 - S3 roots', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The striated sphincter is innervated by the pudendal nerve from the S2 - S3 nerve roots. The neurons that innervate the urethral sphincter originate in the cord, in an area termed Onuf&;s nucleus. The autonomic nervous system also controls the IUS muscle because it is made of smooth muscle fibers.', 'role': 'assistant'}]