Synaptic transmission between pain fibers from the skin and spinal cord neurons is mediated by:

Substance P is found in neurons within the hypothalamus and spinal cord. It is released from small A delta and C fibers that relay information from nociceptors to neurons within the substantia gelatinosa of the spinal cord. Endorphins and other opioid neurotransmitters may paially inhibit the perception of pain by presynaptically inhibiting the release of substance P from nociceptor afferent fibers.