After accidentally hitting her thumb with a hammer, a carpenter immediately grasps and rubs the injured area. She notices that the intense throbbing pain seems to lessen slightly while she is rubbing it. According to the gate control theory of pain, what is the primary mechanism by which rubbing the injured area reduces the sensation of pain?
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The answer
Correct answer: B. The activation of large-diameter nerve fibers inhibits the transmission of pain signals from small-diameter fibers in the spinal cord.
Tested concept: Gate control theory of pain
Explanation
The gate control theory of pain posits that non-painful input can close the 'gates' to painful input, preventing pain sensation from traveling to the central nervous system. When the carpenter rubs her thumb, she activates large-diameter A-beta nerve fibers, which transmit touch and pressure sensations. These large fibers, upon activation, inhibit the transmission of pain signals carried by smaller C and A-delta fibers in the dorsal horn of the spinal cord (the 'gate'), thereby reducing the perceived pain. The option suggesting physical pressure directly blocks pain receptors at the site of injury is incorrect because the theory describes modulation at the spinal cord, not direct receptor blocking. The option proposing that rubbing primarily serves as a psychological distraction describes a psychological factor that can influence pain perception, but it is not the primary physiological mechanism explained by the gate control theory itself. The option involving a rapid release of endorphins describes the action of endorphins, which are involved in pain modulation, but not the immediate, localized 'gating' mechanism described by the theory in response to tactile stimulation.
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