Which nerves are depolarized last and signal pain?

The correct choice is the one that identifies the specific fibers responsible for transmitting pain signals. A-Delta and C fibers, which are types of nociceptive fibers, play a crucial role in signaling sharp and dull pain sensations, respectively. A-Delta fibers are myelinated and conduct signals rapidly, reporting acute, localized pain, while C fibers are unmyelinated and transmit slower, diffuse pain sensations.

The mention of Ad and C fibers aligns with the understanding that these fibers are integral to the body's pain response mechanism. A-Delta fibers (often referred to as Ad fibers in some texts) provide the initial pain sensation due to their faster conduction speed, while C fibers follow up with a prolonged pain signal, thus two distinct fibers are responsible for conveying pain sensations fundamentally.

Motor fibers, on the other hand, are involved in sending signals from the central nervous system to muscles, not in transmitting sensory information like pain. AB fibers, which are responsible for transmitting touch and vibration sensations, do not play a role in pain signaling. Therefore, the identification of the Ad and C fibers as the last to be depolarized, correlates with their role in pain transmission, highlighting their function in the pain signaling pathway.