Altered Neurotransmission (Pain)

Key Terms and Learning Points

Hyperalgesia

Increased sensitivity to pain caused by heightened responsiveness of nociceptive neurons

Allodynia

Pain due to a stimulus that does not usually cause pain, linked to central sensitization

Endorphins

Endogenous opioid peptides that bind to receptors to reduce pain perception

Substance P

A neuropeptide involved in transmitting pain signals and amplifying pain within the spinal cord

Central Sensitization

Enhanced excitability of neurons in the central nervous system, leading to chronic pain

Peripheral Sensitization

Increased sensitivity of peripheral nociceptors to stimuli, often due to inflammatory mediators

Descending Inhibitory Pathways

Neural circuits from the brainstem that modulate and inhibit pain transmission at the spinal level

Pain

Negative psychological response to stimulus causing sensory or emotional experiences, not measured

Types of pain

nociceptive, inflammatory, neuropathic, dysfunctional

Nociceptive pain

pain from acute tissue injury

Inflammatory pain

pain driven by sensitization at injury sites from inflammatory mediators

Neuropathic pain

Pain caused by nerve injury

Nociception

Physiological response of detecting and transmitting a harmful stimulus

Acute pain

Beneficial physiologic process that serves an adaptive purpose to warn about harmful situations

Chronic pain

Harmful physiologic process that keeps person in a pathologic pain state

Musuloskeletal pain

Localized somatic pain

Visceral pain

Deep internal organ pain

Dysfunctional/Nociplastic pain

Maladaptive central pain processing without clear peripheral cause

Transduction

Activation of peripheral nociceptors by noxious stimuli (receive signal from outside the body)

Transmission

Propagation of pain signals via afferent nerves to spinal cord and brain

Perception

Integration of sensory, emotional, and cognitive components in brain regions such as the thalamus and cortex

Modulation

Descending pathways inhibit or enhance pain signals via neurotransmitters such as serotonin, endorphins, and norepinephrine

A delta fibers

acute, localized pain; slow with large diameter

C fibers

Dull, arching, diffuse pain; very slow with small diameter

A-beta fibers

Sensations of light touch; very fast with large diameter

Major excitatory neurotransmitter at the first synapse released by C and A delta fibers

Glutamate

Inhibitory neuromodulators

GABA, NE, serotonin

Potentiating neuromodulators

Glu, substance P, histamine

Pain hypersensitivity 

Core symptom is an amplified pain response including both allodynia and hyperalgesia

3 families of endogenous opioid peptide in mammals

beta-endorphins, enkephalins, dynorphins

Monoamines (serotonin, norepinephrine)

Modulate pain via descending inhibitory tracts