Pain, Cutaneous Mechanoreceptors, & Sensory Nerve Fibers

nociceptive pain

pain arising from actual or threatened tissue, transmitted via normally-functioning nociceptors

neuropathic pain

pain caused by abnormal neural activity, NOT tissue damage

paresthesia

painless abnormal tingling/pricling

dyesthesia

unpleasant abnormal sensation (burning, shooting, “electrical”)

allodynia

pain from normally non-painful stimuli (light touch)

secondary hyperalgesia

exaggerated response to mildly painful stimuli

peripherally generated

mononeuropathies, nerve entrapment, nerve compression

CNS response to deafferentation

dorsal root avulsion, phantom limb pain (cortical reorganization overlaps)

central pain syndromes

lesions within the CNS (ex SCI, CVA, MS)

small fiber neuropathy

partial deafferentation + central sensitization (ex diabetic neuropathy, GBS)

pain matrix dysfunction

abnormal regulation of pain from higher centers —> imbalance between inhibition & amplification (ex fibromyalgia, episodic tension-type headache, migraine, chronic whiplash disorder)

CRPS

pain + vascular changes = atrophy

early: red/pale skin, sweating, edema

late: dry/cold skin, stiff/swollen joints

chronic low back pain syndrome

shift from tissue damage —> maladaptive guarding, abnormal movement, disuse, & emotional distress

size & myelination

Ia fiber

large & heavily myelinated

size & myelination

Ib fibers

large & heavily myelinated

size & myelination

Aβ fibers

large & myelinated

size & myelination

A∂ fibers

small & thinly myelinated

size & myelination

C fibers

small & unmyelinated

receptor type

Ia fibers

muscle spindle

receptor type

Ib fibers

GTO

receptor type

Aβ fibers

cutaneous mechanoreceptors

receptor type

A∂ fibers

thermoreceptors & nociceptors

receptor type

C fibers

thermoreceptors & nociceptors

main function

Ia fibers

muscle stretch & velocity

main function

Ib fibers

muscle tension & force

main function

Aβ fibers

detect touch, vibration, & pressure

main function

A∂ fibers

detect fast pain (sharp), cold, & crude touch

main functions

C fibers

detect slow pain (dull/aching), heat, itch, tickle

fast or slow:

merkel’s discs

slow

fast or slow:

meissner’s corpuscles

fast

fast or slow:

pacinian corpuscles

fast

fast or slow:

ruffini endings

slow

function

merkel’s discs

fine details, edges, texture discrimination

function

meissner’s corpuscles

light touch, flutter, motion across skin

function

pacinian corpuscles

high-frequency vibrations, deep pressure

function

ruffini endings

skin stretch, sustained pressure, grip modulation

OT application

merkel’s discs

reading Braille, feeling ridges of coins

OT application

meissner’s corpuscles

detecting clothing brushing across skin, mosquito landing on arm

OT application

pacinian corpuscles

feeling vibrations when using a power tool, sensing phone vibrations

OT application

ruffini endings

adjusting grip on a glass of water to prevent slipping or crushing