Reading: Touch and Pain

Touch

Sense that conveys information about the environment and body

Pain

Sense that signals potential tissue damage

Somatosensory system

System connecting the skin and body to the brain

Cutaneous senses

Senses of the skin responding to tactile

Proprioception

Sense of body position

Kinesthesis

Sense of body movement

Nociception

Sense of pain and discomfort from tissue damage

Affective touch

Pleasant touch that contributes to social bonding and emotional well-being

Transduction

Conversion of a stimulus (mechanical

Mechanoreceptors

Receptors responding to mechanical stimuli such as pressure

Thermoreceptors

Receptors responding to hot or cold temperatures

Chemoreceptors

Receptors responding to chemical stimuli applied externally or released in the skin

Nociceptors

Receptors that fire specifically to potentially tissue-damaging stimuli

A-afferents

Fast-conducting nerve fibers that signal sharp

C-afferents

Slow-conducting fibers signaling diffuse

Aδ-fibers

Thin myelinated fibers conveying fast pain signals

C-pain fibers

Unmyelinated fibers conveying slow

Somatotopic organization

Spatial mapping of the body on the somatosensory cortex

Sensory–discriminatory aspect of pain

Allows localization and characterization of a painful stimulus

Affective–motivational aspect of pain

Signals unpleasantness and emotional response to pain

C-tactile fibers

Subtype of C-fibers that respond to gentle

Social touch hypothesis

C-tactile system forms a system for touch perception that supports social bonding

Motivation–decision model

Brain evaluates threats and rewards to modulate pain perception

Descending pain modulation

Top-down system from brain and brainstem that inhibits or facilitates nociceptive signaling

Periaqueductal gray (PAG)

Midbrain structure that modulates pain signals via descending pathways

Rostral ventromedial medulla (RVM)

Brainstem region that mediates inhibitory and facilitatory control of spinal nociceptive signals

ON-cells

Cells in the RVM that facilitate nociceptive transmission

OFF-cells

Cells in the RVM that inhibit nociceptive transmission

Endogenous opioids

Natural pain-relieving chemicals released by the brain

Analgesia

Reduction or suppression of pain

Reward-induced analgesia

Reduction of pain through anticipation or receipt of reward

Placebo effect

Pain relief due to expectation of treatment mediated by descending modulation and endogenous opioids

Allodynia

Condition where innocuous touch is perceived as painful

Chronic pain

Pain persisting beyond normal healing

Peripheral sensitization

Increased excitability of nociceptors after tissue injury

Central sensitization

Increased excitability of neurons in the spinal cord or brain contributing to persistent pain

Top-down modulation

Influence of motivation

Empathy for pain

Activation of brain areas for pain when observing others in pain

Vicarious touch

Activation of touch-related brain areas when observing others being touched

Distraction

Technique to temporarily reduce pain perception by diverting attention

Social support

Hand-holding or presence of loved ones reduces pain perception

Contextual modulation

Perception of pain or touch depends on situational context and meaning