The gate-control theory of pain suggests that:

A) the pain signals must pass through a kind of "gate" located in the spinal cord.
B) the skin receptors act as a gate for the pain sensation.
C) the cortex blocks pain unless released by substance P.
D) the gate is a physical structure that blocks pain signals.

Answer: A
Rationale: A long-held theory of pain perception is called gate-control theory, which explains our experience of pain as an interaction between nerves that transmit pain messages and those that inhibit these messages. Cells in the spinal cord regulate how much pain signaling reaches the brain. Thus, the spinal cord serves as a "neural gate" that pain messages must pass through.