Pain Processing and Sensitization Review

Vocabulary and concepts based on lecture notes covering pain mechanisms, dorsal horn anatomy, central and peripheral sensitization, and the neurobiology of chronic stress.

Interneurons

Cells in the dorsal horn of the spinal cord that meet nociceptor input from the periphery and perform modulation and filtering by either blocking info or allowing it to pass to the 2nd order neuron.

2nd order neurons

Neurons that take passed information from the spinal cord Rexed Laminae and send it to the brain.

Marginal layer

The term for Rexed Laminae $I$ in the spinal cord dorsal horn involved in processing nociception.

Substantia gelatinosa

The term for Rexed Laminae $II$ in the spinal cord dorsal horn involved in processing nociception.

Nucleus proprius

The term for Rexed Laminae $IV$ in the spinal cord dorsal horn involved in processing nociception.

A-Beta Fiber

Nerve fibers that normally respond to light touch; during neuroplastic changes, these can grow into center laminae and become part of the nociceptive system.

C Fiber

Nerve fibers that carry danger signals into the CNS and may pull back out of center laminae during constant nociceptive barrage.

Peripheral sensitization

Increased responsiveness of nociceptors in the peripheral nervous system due to acute tissue damage.

Central sensitization

Increased responsiveness of nociceptive neurons in the central nervous system to their normal or subthreshold afferent input.

Hyperalgesia

Increased pain response from a stimulus that normally provokes pain.

Allodynia

Pain response from a stimulus that normally does not provoke pain.

Anti-nociception

Top-down inhibition of pain signals using descending pathways and chemicals like endorphins and enkephalins.

Pro-nociception

Bottom-up amplification of pain signals via local release of glutamate, aspartate, $Substance\,P$, and prostaglandins.

Spinothalamic tract

The lateral ascending nociceptive tract responsible for communicating location and intensity to the brain.

Divergent pathways

The medial ascending nociceptive tracts responsible for affective and cognitive processing.

Pain Neuromatrix

Brain structures (brainstem, limbic system, hypothalamus, thalamus, and cerebral cortex) that process and regulate pain information and can create pain perception without nociceptive input.

Cortical smudging

A condition where cortical body representations are altered and have increased activation, leading to pain perception in the absence of peripheral stimulation.

Laterality

The ability of a patient to perform left-right discrimination, which can be impaired in chronic pain states.

Cortisol

A stress chemical that acts longer than adrenaline, impacting the immune system and causing tissues to feel sore, tired, sensitive, and fatigued.

Fibromyalgia

A clinical disease that can result from an overworked immune system due to persistent pain stressors.

Adrenal fatigue

A clinical consequence of an overworked sympathetic nervous system.

Irritable bowel syndrome

A clinical disease that can result from an overworked gastrointestinal system.

Chronic fatigue syndrome

A clinical disease originating from an overworked endocrine system.

Homuncular smudging

Structural shifts in the brain's sensory homunculus associated with chronic pain.