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: Physiology
[{'content': 'Human body has rhythmic fluctuations in their function on a circadian cycle. Circadian rhythm is controlled by: \nSelect and explain. \nA. Suprachiasmatic nuclei, B. Median eminence, C. Paramedian nuclei, D. Supraoptic nuclei', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Within the hypothalamus, a specific cell group, the suprachiasmatic nucleus, functions as an intrinsic clock. Cells within this nucleus show circadian rhythms in metabolic and electrical activity, and in neurotransmitter synthesis, and appear to keep the rest of the brain on a day-night cycle. Ref: Waxman S.G. (2010). Chapter 9. Diencephalon. In S.G. Waxman (Ed), Clinical Neuroanatomy, 26e.', 'role': 'assistant'}]