This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nerve, Subject name: Physiology
[{'content': 'Velocity of impulse transmission is least in the nerve fiber: \nSelect and explain. \nA. Aa, B. Ab, C. B, D. C', 'role': 'user'}, {'content': 'Answer: D \nExplanation: C fiber is unmyelinated and it has least diameter among all the fiber types. Its conduction velocity is the slowest. For unmyelinated nerves: Conduction velocity is propoional to the square root of the diameter. Hence, faster conduction velocity is primarily based on the diameter alone. A greater diameter means less axoplasmic resistance for the flow of ions. In addition, myelin decreases the effective resistance of the membrane.', 'role': 'assistant'}]