What physical attributes of the peripheral nerves cause the fastest conduction velocities?

The fastest conduction velocities in peripheral nerves are attributed to their larger diameter and myelination. Larger diameter axons facilitate quicker conduction due to a reduced internal resistance, allowing electrical impulses to travel more rapidly along the nerve.

Myelination plays a critical role by providing insulation around the axon. This insulating layer allows for saltatory conduction, where the nerve impulse jumps from one node of Ranvier (a small gap in the myelin sheath) to another, significantly speeding up transmission compared to continuous conduction in unmyelinated fibers.

Thus, the combination of a larger diameter, which reduces resistance to current flow, and myelination, which increases the speed of signal propagation through saltatory conduction, accounts for the fastest conduction velocities observed in certain types of peripheral nerves.