This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
[{'content': 'External anal sphincter is innervated by? \nSelect and explain. \nA. S2,S3,S4, B. S2, S3, C. S1,S2, D. L5,Sl', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is'a' i.e.,S2, S3, S4Anal Sphincters :Two sphincters, internal and external, surround the anal canal:A. Internal sphincter (sphincter ani internus):InvoluntarySympathetic fibers through superior hypogastric plexus aParasympathetic fibers from pelvic splanchnic nerves (S2 S3 S4). B. External sphincter (sphincter ani externus)VoluntarySurrounds the entire length of anal canalInferior rectal nerve (S2 S3 S4) and perineal branch", 'role': 'assistant'}]