Pain and Temperature Regulation Flashcards

Vocabulary flashcards covering pain neuroanatomy, pain theories, neuromodulators, pain classification, thermoregulation, fever, hyperthermia disorders, and hypothermia.

Pain (IASP Definition)

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

Gate Control Theory

A theory explaining pain mechanics where a "gate" in the spinal cord controls pain impulses reaching the brain. A open gate allows full pain signals through, while a partially or fully closed gate (via mechanisms like massage, relaxation, or analgesics) reduces pain transmission.

Basic Anatomy of Nociception

The neural pathway consisting of free nerve ending nociceptors in peripheral tissue, peripheral nerves, spinal cord, and brain responsible for sensing and transmitting tissue injury signals.

Nociceptors

Free nerve endings located in skin, muscle, joints, arteries, and viscera that detect chemical, mechanical, and thermal stimuli.

A-delta ($A\,\delta$) Fibers

Myelinated, faster-conducting nerve fibers responsible for transmitting sharp and well-localized pain signals.

Unmyelinated $C$ Polymodal Fibers

Slow-conducting, unmyelinated nerve fibers that transmit dull, aching, and poorly localized pain sensations.

Pain Transduction

The process of activating nociceptors by chemical, mechanical, or thermal tissue-damaging stimuli.

Pain Transmission

The conduction of pain impulses along sensory nerve fibers to the dorsal horn of the spinal cord and up to higher brain centers.

Pain Pathways and Modulation Diagram

Anatomy showing ascending spinothalamic tracts carrying pain signals to the thalamus/cortex, alongside descending pathways where pain inhibitors (e.g., opioids, GABA) and pain facilitators (e.g., Substance P, glutamate) regulate pain perception.

Excitatory Neuromodulators

Neurotransmitters in the CNS and PNS, such as Substance P and glutamate, that trigger and increase pain signal transmission following tissue injury or inflammation.

Inhibitory Neuromodulators

Neurotransmitters such as GABA, glycine, serotonin, and norepinephrine that inhibit or suppress pain transmission in the nervous system.

Endorphins

Endogenous opioids that block pain transmission by binding to mu, kappa, and delta opioid receptors in descending inhibitory pathways.

Acute Pain

A protective physiological mechanism alerting the individual to immediate harm, characterized by fight-or-flight responses including tachycardia, hypertension, diaphoresis, dilated pupils, fever, elevated blood sugar, and decreased intestinal motility.

Somatic Pain vs. Visceral Pain Features

Somatic pain arises from skin, muscle, or bones and is sharp/well-localized or throbbing/aching. Visceral pain arises from internal organs/smooth muscle, is sensitive to stretch, hypoxia, and inflammation, and is poorly localized, vague, referred, and often accompanied by autonomic symptoms.

Referred Pain Sites

Pain perceived in an area distant from its site of origin because both areas are innervated by the same spinal segment (e.g., heart pain referred to the left chest and arm, or diaphragm pain referred to the shoulder).

Chronic Pain

Persistent or intermittent pain lasting at least $3$ to $6$ months that produces significant behavioral and psychological changes, typically lacking the acute physiological fight-or-flight signs.

The Chronic Pain Cycle

A self-reinforcing cycle where chronic pain leads to decreased activity/deconditioning, avoidance/withdrawal, negative emotions/catastrophizing, and increased pain perception.

Myofascial Pain Syndromes

A chronic pain condition caused by injury to muscle and fascia, presenting with muscle spasms, tenderness, and stiffness.

Neuropathic Pain

Pain resulting from trauma or disease of non-nociceptive nerves, categorized into peripheral (e.g., painful diabetic neuropathy) and central (e.g., phantom limb pain).

Pain Threshold

The lowest intensity of a stimulus that a person can recognize as pain.

Pain Tolerance

The maximum level or duration of pain that a person is willing to endure, increased by factors like opioids and distraction, and decreased by fatigue or anxiety.

Fever (Pyrexia)

Temporary elevation of body temperature ($99.4^{\circ}\text{F}$ to $100.4^{\circ}\text{F}$ or higher) caused by resetting of the hypothalamic thermostat set point in response to pyrogens.

Exogenous Pyrogens

Fever-producing agents originating outside the body, such as viruses and bacteria.

Endogenous Pyrogens

Internal fever-producing signaling molecules (such as interleukins and tumor necrosis factor) released by host macrophages and phagocytes.

Benefits of Fever

Host defense benefits including killing or inhibiting microorganism growth, lowering serum iron and zinc required for bacterial replication, promoting lysosomal breakdown, and enhancing phagocytosis.

Hyperthermia

An elevation in body temperature not mediated by pyrogens, with no resetting of the hypothalamic set point. Convulsions occur at $41^{\circ}\text{C}$ ($105.8^{\circ}\text{F}$) and death at $43^{\circ}\text{C}$ ($109.4^{\circ}\text{F}$).

Hyperthermia Severity Spectrum

The progression of heat-related illnesses ranging from least severe to most severe: Heat Rash, Heat Cramps, Heat Syncope, Heat Fatigue/Exhaustion, to Heat Stroke (death).

Heat Cramps

Severe spasmodic cramps in the abdomen and extremities following prolonged sweating and sodium loss, accompanied by fever, rapid pulse, and increased blood pressure.

Heat Exhaustion

A condition resulting from prolonged high core or environmental temperatures, leading to vasodilation, profuse sweating, dehydration, hypotension, tachycardia, dizziness, weakness, nausea, confusion, and syncope.

Heat Stroke

A life-threatening failure of the thermoregulatory center when core temperature exceeds $40^{\circ}\text{C}$ ($104^{\circ}\text{F}$), characterized by red, hot, dry skin (no sweating), rapid strong pulse, throbbing headache, cerebral edema, and potential coma or death.

Heat Exhaustion vs. Heat Stroke Clinical Comparison

Clinical distinction where heat exhaustion features cool/pale/clammy skin, excessive sweating, and rapid weak pulse, whereas heat stroke features red/hot/dry skin, absence of sweating, body temperature above $103^{\circ}\text{F}$, rapid strong pulse, and urgent emergency service need.

Malignant Hyperthermia

An inherited autosomal dominant muscle disorder triggered by inhaled anesthetics and neuromuscular blockers, causing uninhibited calcium release, sustained muscle contraction, hypermetabolism, absent reflexes, fixed pupils, and flat ECG.

Hypothermia

Core body temperature dropping below $35^{\circ}\text{C}$ ($95^{\circ}\text{F}$), causing CNS and respiratory depression, vasoconstriction, increased blood viscosity, ischemic tissue damage, and cellular rupture from intracellular ice crystals.

Accidental Hypothermia

Unintentional hypothermia resulting from sudden immersion in cold water or prolonged exposure to cold environments.

Therapeutic Hypothermia

Controlled cooling used medically (e.g., lowering body temperature to $33.5^{\circ}\text{C}$ for $72\text{ hours}$ in newborns with hypoxic-ischemic encephalopathy) to slow metabolic rate, preserve tissue, and limit neurological damage.

Targeted Temperature Management (TTM)

A clinical procedure using cooling equipment to precisely control body temperature in patients to slow metabolic consumption and protect neural function post-cardiac arrest.

Radiation (Heat Loss)

The loss of body heat to the cooler surrounding environment via electromagnetic waves without physical contact.

Conduction (Heat Loss)

The direct transfer of body heat to a cooler object through physical contact.

Convection (Heat Loss)

The loss of body heat carried away by moving currents of air or liquid.

Evaporation (Heat Loss)

Heat dissipation occurring when liquid body sweat transitions into gas/vapor.