Fig. 1.

Sites and mechanisms of pain. (A) Schematics of the nociceptive/pain pathways from periphery to brain. Painful stimuli activate and depolarize the peripheral terminals of nociceptors. Action potentials are then transmitted along the afferent axons to the spinal cord. Neurotransmitters released from nociceptive neurons activate spinal neurons that send pain signals across the spinal cord and up specific fiber tracts, terminating in the medulla, midbrain, and thalamus. Projections from thalamic neurons relay these signals to regions of the cortex including the somatosensory cortex where the neural signals are interpreted as pain localized to a specific body region. (B) Pain sites and related subtypes.