Thermal heating of ultrasonography decreases pain perception by

• A. Slowing nerve conduction velocity
• B. Increasing nerve conduction velocity
• C. No effect on nerves
• D. Pain increases

Answer: (A)

Thermal heating from ultrasound affects nerve signaling in a way that can reduce pain perception. By raising tissue temperature, the transmission of nerve impulses—especially those carrying nociceptive (pain) signals—can be dampened, so fewer pain impulses reach the spinal cord and brain per unit time. This slower transmission helps create a higher pain threshold and contributes to analgesia. In practice, warming also aids muscle relaxation and tissue extensibility, which supports comfort, but the primary mechanism highlighted here is the reduction in how quickly pain signals are conducted.