PATH1016 - PAIN 2025-26 Lecture Notes

Flashcards covering the etiology, theories, physiology, pathways, and types of pain based on the PATH1016 lecture transcript.

Pain

An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

First-order neurons

Sensory neurons that transmit information from the periphery to the spinal cord.

Second-order neurons

Sensory neurons that transmit information from the spinal cord to the thalamus.

Third-order neurons

Sensory neurons that transmit information from the thalamus to the cerebral cortex.

Specificity theory

A pain theory stating that special pain receptors called nociceptors detect pain, and the intensity of pain is related to the amount of tissue injury.

Pattern theory

A pain theory suggesting that sensory receptors create pain signals when stimuli are too strong.

Gate control theory

A theory stating that pain is carried by distinct fibers in the spinal cord and a spinal gate regulates pain transmission to higher centers in the CNS.

Neuromatrix theory

A theory stating that the brain identifies pain.

Mechanical stimuli

A type of pain stimulus involving intense pressure applied to the skin or extreme stretch of muscles.

Thermal stimuli

A type of pain stimulus caused by heat or cold.

Chemical stimuli

A type of pain stimulus caused by tissue trauma, ischemia, or inflammation involving mediators such as $K^{+}$, $H^{+}$ ions, prostaglandins, leukotrienes, histamine, and bradykinin.

Transduction

The first step of pain transmission where noxious stimulation causes the release of chemical mediators from damaged cells and initiates an action potential.

Transmission

The second step of pain physiology where impulses travel from the spinal cord towards the brain via nerve fibers like A delta and C fibers.

Perception

The third step of pain physiology where pain signals enter the brain and the sensation reaches consciousness, including sensations of hurtfulness and meaningfulness.

Modulation

The process of dampening or amplifying pain-related nerve signals, primarily taking place in the dorsal horn of the spinal cord.

A-delta fibers

Large, myelinated fibers that travel quickly to the thalamus to transmit "fast pain" or "first pain" and release glutamate at the synapse.

C fibers

Small, non-myelinated fibers that travel slowly to the brain stem, thalamus, and cortical centers to transmit "slow pain" and release glutamate and substance P.

Paleospinothalamic tract

An anterolateral pathway with slower conduction that goes to the reticular activating system and limbic system, affecting arousal, mood, and attention.

Neospinothalamic tract

An anterolateral pathway with fast conduction that goes to the thalamus and parietal cortex, allowing for the localization and identification of pain.

Periaqueductal gray (PAG) region

An area in the midbrain with a high number of opioid receptors that produces analgesia through the release of endogenous opioids.

Dermatomes

Areas of the body wall where sensation is supplied by a single pair of dorsal root ganglia.

Neuropathic pain

A complex, chronic pain state usually accompanied by tissue injury where nerve fibers themselves are damaged, dysfunctional, or injured, sending incorrect signals to pain centers.

Neuralgia

A sharp, shocking pain that follows the path of a nerve, characterized by severe, brief, and often repeated throbbing pain.

Trigeminal neuralgia

A nerve disorder causing stabbing or electric-shock-like pain in parts of the face due to damage or irritation to the Trigeminal nerve.

Post-herpetic neuralgia

A type of neuralgia caused by a herpetic infection, such as shingles.

Neurogenic Inflammation

A process where tissue damage and inflammatory mediators stimulate nociceptors, leading to a dorsal nerve root reflex that releases mediators back into the tissues.