Which nerve fiber type is fastest conducting?

Which nerve fiber type is fastest conducting?

• A. C fibers
• B. A beta fibers
• C. 1A fibers (FASTEST)
• D. A gamma fibers

Answer: (C)

Conduction velocity depends mainly on axon diameter and the presence of myelin. Larger-diameter, heavily myelinated fibers conduct fastest because myelin increases membrane resistance and saltatory conduction jumps impulses from node to node, greatly speeding transmission. Ia fibers are large-diameter, heavily myelinated A fibers that innervate muscle spindles. This combination yields the highest conduction speeds among peripheral fibers, so they conduct impulses the fastest. In contrast, C fibers are unmyelinated and slow, while A-beta and A-gamma fibers are myelinated but smaller in diameter, making them slower than Ia. This is why Ia fibers are the quickest conduits for proprioceptive information and rapid reflexes.

Conduction velocity depends mainly on axon diameter and the presence of myelin. Larger-diameter, heavily myelinated fibers conduct fastest because myelin increases membrane resistance and saltatory conduction jumps impulses from node to node, greatly speeding transmission.

Ia fibers are large-diameter, heavily myelinated A fibers that innervate muscle spindles. This combination yields the highest conduction speeds among peripheral fibers, so they conduct impulses the fastest. In contrast, C fibers are unmyelinated and slow, while A-beta and A-gamma fibers are myelinated but smaller in diameter, making them slower than Ia. This is why Ia fibers are the quickest conduits for proprioceptive information and rapid reflexes.