What happens during Perception?

The perception of pain is an uncomfortable awareness of some part of the body, characterized by a distinctly unpleasant sensation and negative emotion best described as threat. Both cortical and limbic system structures are involved. Immediate social and environmental context influences the perception of pain, as do past experience and culture. Consequently, a standard cause of pain (e.g. surgery) can generate enormous individual differences in pain perception.¹

What happens during Modulation?

Descending pathways: modulation of nociceptive transmission occurs at multiple (peripheral, spinal, supraspinal) levels. Historically, modulation has been viewed as the attenuation of DH transmission by descending inhibitory input from the brain.
Multiple brain regions contribute to descending inhibitory pathways.¹

What happens during Transmission?

Nerve impulses generated in the periphery are transmitted to the spinal cord and brain in several phases.¹

• Periphery to the spinal cord: most sensory nerve impulses travel via the nerve processes (axons) of primary afferent neurons to the dorsal horn (DH) of the spinal cord.
• Spinal cord to the brain: the nerve processes of DH projection neurons project to the brain in bundles called ascending tracts.

What happens during Transduction?

Nociceptors are sensory receptors that are preferentially sensitive to tissue trauma or a stimulus that would damage tissue if prolonged. These receptors are the free endings of (primary afferent) nerve fibers distributed throughout the periphery.¹

• Injury to tissue causes cells to break down and release various tissue byproducts and mediators of inflammation.
• Some of these substances activate nociceptors (i.e., cause them to generate nerve impulses) and most sensitize nociceptors (i.e., increase their excitability and discharge frequency).