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
Velocity of impulse transmission is least in the nerve fiber: 
Select and explain. 
A. Aa, B. Ab, C. B, D. C
D: C
Answer: D: C 
Explanation: 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.