Final answer:
In the gate-control theory of pain, the major "gate" is located in the spinal cord and brainstem where pain sensory neurons enter to synapse on second-order pain neurons. The third neurons in the thalamus further relay the information to the somatosensory cortex for conscious perception of the pain stimulus. Option c is correct.
Step-by-step explanation:
The major "gate" in the gate-control theory of pain is the point where pain sensory neurons enter the spinal cord and brainstem to synapse on second-order pain neurons. These sensory neurons carry nociceptive information from the body to the brain. The spinothalamic pathway carries nociceptive information from the body to the brain, with the second neurons in the dorsal horn of the spinal cord decussating within the spinal cord and ascending to the thalamus.
In the spinothalamic pathway, the axons from the second neurons in the dorsal horn of the spinal cord decussate within the spinal cord and ascend to the brain, entering the thalamus where they synapse with third neurons in their respective pathway. The third neurons in the thalamus then project their axons to the somatosensory cortex where the conscious perception of the pain stimulus occurs.