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: Surgery
[{'content': 'Synaptic transmission between pain fibers from the skin and spinal cord neurons is mediated by: \nSelect and explain. \nA. Acetylcholine, B. Substance P, C. Endorphins, D. Somatostatin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Substance P is found in neurons within the hypothalamus and spinal cord. It is released from small A delta and C fibers that relay information from nociceptors to neurons within the substantia gelatinosa of the spinal cord. Endorphins and other opioid neurotransmitters may paially inhibit the perception of pain by presynaptically inhibiting the release of substance P from nociceptor afferent fibers.', 'role': 'assistant'}]