Pain and Nociception

Pain Definition

• Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage.
• Defined by the International Association for the Study of Pain.

Pain Mechanism

• Sensation and nociception involve a three-neuron sequence: receptor or free nerve ending → 1st order neuron (A-β, A-δ, C fibers) → dorsal horn.

Descending Pathways

• Activity (excitatory or inhibitory) occurs after the cortex receives input.
• Pain can be managed by targeting descending pathways.

Pain Control Theories

Peripheral Pain Modulation

• Desensitize peripheral nociceptors to manage pain.
• Slow conduction velocity is usually achieved with cryotherapy.

Spinal Level Pain Modulation

• Gate control theory proposes a gating mechanism in the dorsal horn of the spinal cord.
• A-β, A-δ, and C fibers all synapse with 2nd order neurons in the dorsal horn.
• Substantia gelatinosa (SG) has inhibitory interneurons that inhibit transmission between 1st and 2nd order nociceptive neurons.
• Enkephalin interneurons release enkephalin, a natural opioid, to inhibit pain transmission.
• A-β impulses stimulate SG, resulting in enkephalin release and inhibition of A-δ and C fiber transmission to 2nd order neurons.

Pain Modulation

• Pain modulation involves both ascending and descending neural components.
• Supraspinal refers to modulation that occurs above the level of the spinal cord.
• Descending refers to modulation that travels from the brain to the spinal cord or brainstem.

Noxious Pain Modulation

• Noxious pain modulation involves the elicitation of C-fibers in af.

Explore the unpleasant sensory and emotional experience of pain, including its definition, sensation, and pathways. Learn about the three-neuron sequence and descending pathways that manage pain.