Final answer:
Substance P is the chemical that releases at the spinal cord to increase pain, unlike endorphins, which reduce pain, or serotonin and acetylcholine, which have other functions in the body.
Step-by-step explanation:
The substance that releases chemicals at your spinal cord to increase pain is Substance P. Endorphins actually work to diminish pain by binding to opioid receptors, which can decrease the perception of pain. Serotonin can modulate pain, but it doesn't directly increase pain sensation at the spinal cord as Substance P does. Acetylcholine is involved in the activation of muscles and is not directly associated with the transmission of pain signals.