Which of the following statements regarding the gating theory of pain is correct:

Correct Answer: B

Rationale: Massage applied to the skin over a painful joint may reduce pain sensitivity . The gate control theory posits that non-painful input (e.g., touch via large A-beta fibers) can inhibit pain signals (A-delta, C fibers) at the spinal cords dorsal horn via interneurons, reducing pain perception. Massage activatA-beta fibers, supporting this. Choice A is wrong (small fibers transmit pain). Choice C is incorrect (A-delta/C fibers increase pain). Choice D is false (large fiber loss increaspain). Thus, B aligns with the theory, making it correct.

Correct Answer: D

Rationale: 55% of its fibers synapse in the upper cervical region . The anterior corticospinal tract, uncrossed, acts on axial muscl, passthrough the pons basilar part and midbrain pedunculi , but only about 10-20% remain uncrossed, with most synapsing lower, not 55% in cervical. Thus, D overestimatcervical synapses, making it the wrong statement and the correct answer.

Correct Answer: D

Rationale: In front of the central sulcus. Fine hand movements are controlled by the primary motor cortex, in the precentral gyrus, anterior to the central sulcus. Choice A (temporal gyrus) is for audition. Choice B (postcentral) is sensory. Choice C (medial brain) includleg areas. Thus, D correctly locatthe hand motor area, making it correct.

Correct Answer: D

Rationale: Anterior limb of the internal capsule . Corticospinal fibers travel through the posterior limb of the internal capsule, not anterior (frontopontine fibers). Choice A (medulla pyramid), B (lateral column), and C (cerebral peduncle) all contain corticospinal fibers. Thus, D is the exception, making it correct.

Correct Answer: B

Rationale: Damage to corticospinal tract above the level of decussation results in contralateral loss of motor function . The corticospinal tract originatin the motor cortex (not brainstem, making A incorrect) and descends through the internal capsule, midbrain, pons, and medullary pyramids, where most fibers (85-90%) decussate in the lower medulla (not upper, making D wrong) to form the lateral corticospinal tract. Above the decussation (e.g., cortex or brainstem), fibers are ipsilateral, so damage (e.g., stroke) causcontralateral motor deficits, as seen in hemiplegia, supporting B. Below the decussation (in the spinal cord), fibers are contralateral, so damage causipsilateral loss (making C incorrect). For example, a right medullary lesion below decussation affects the right spinal cord, causing right-sided weakness, not contralateral. Thus, B accurately describthe effect of damage above decussation, making it the correct answer.