This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
[{'content': 'Thickening of axon leads to \nSelect and explain. \nA. Increased speed of conduction, B. Decreased speed of conduction, C. Increased absolute refractory period, D. Unmyelination', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Thickening of axon leads to increased speed of conduction as the action potential velocity increases propoionately with axon diameter. Ref: guyton and hall textbook of medical physiology 12 edition page number:76,77,78', 'role': 'assistant'}]