Pain Pathways and Modulation

Which neurotransmitter is primarily responsible for presynaptic inhibition of nociceptive input at the dorsal horn of the spinal cord?

A patient receives morphine for postoperative pain relief. The analgesic effect is mediated primarily through which spinal cord pathway and mechanism?

A 58-year-old man from Delhi presents with severe, burning pain in his left leg following a motor vehicle accident 6 months ago. The pain is described as constant, with a sensation of 'pins and needles' and occasional electric shock-like quality. Physical examination reveals allodynia (pain with light touch) and hyperalgesia (exaggerated pain response to pinprick) in the affected limb. Nerve conduction studies and imaging are normal. He has already tried NSAIDs and paracetamol without relief. Which of the following mechanisms best explains the persistent pain despite normal structural imaging?

Regarding the spinothalamic tract and pain transmission, all of the following statements are correct EXCEPT:

Regarding pain modulation and the descending inhibitory system, all of the following are true EXCEPT: