Nociceptors

Nociception

physiological process of transduction of impending or actual tissue damage

Pain

a subjective and perceived experience of actual or impending harm (physical, emotional, empathetic)

Acute Pain Timing

less than 6 months

Characteristics of acute pain

sudden onset, trigger inflammation or nociceptive pain

Chronic Pain Timing

longer than 6 months

Characteristics of Chronic pain

persistent stimulus, either nociceptive or neuropathic, gradual onset, difficult to find lasting relief

Noxious stimuli

harmful, injuries to physical health or well-being, typically temp, chemicals, or tissue damage

Neuropathic Pain

disease or damage mediated directly to sensory nerves, cause of chronic pain

Common descriptions of neuropathic pain

pins and needles, burning, tingling, painful cold, electrical shock

Trigeminal Neuralgia

peripheral pain, facial pain

Postherpetic neuralglia

peripheral pain on one side corresponding to dermatomes

peripheral nerve injury pain

peripheral pain occurring where injured nerve is and distal to it

Post-amputation pain

peripheral pain, phantom limb pain

Painful Polyneuropathy

peripheral pain in hands and feet

Painful radiculopathy

peripheral pain from nerve root injury

Neuropathic pain with SCI

central pain at or below level of SCI

Central Post-stroke pain

central pain contralateral to sign of stroke

Neuropathic Pain with MS

central pain along spinal cord

Nociceptive threshold

from physical or chemical damage to tissue, detected at high thresholds

Purpose of nociceptors

protect body from damage, flight or flight response, draw attention to danger

Nociceptors at rest

typically silent without stimulation, neither phasic or tonic

AP firing of nociceptors

not stronger than any other AP, but fire more frequently

Nociceptor significance over other sensory receptors

takes priority, overriding stimulus

Nociceptor External Locations

skin, cornea, mucosa (all interacting with environment)

Nociceptor Internal Locations

everywhere so we are aware when our life is threatened

Trigeminal ganglion

nociceptor cell body for face from trigeminal nerve

Dorsal Root Ganglion

nociceptor cell body for rest of body from spinal nerve

c-fibers

unmyelinated, small diameter

c-fiber subtypes

mechanical, mechanocold, mechanoheat (polymodal)

Silent c-fibers

only active once inflammation sensed

A- and A-delta fibers

myelinated, large diameter

A- and A-delta fiber subtypes

heat, cold, mechanothermal (polymodal)

Free nerve ending fiber types

c-fibers, A- and A-delta fibers (slow and fast)

Free nerve ending timing

a-fibers activated first, then c-fibers

A- and A-delta fiber function

fast, extreme, sharp pain

c-fiber function

prolonged, less intense pain

Ion Channels

fast acting to control nociceptor response

Spinal response to noxious stimuli

withdrawal reflex using reciprocal inhibition

Central response to noxious stimuli

associate pain with object for avoidance and survival

Local response of nociceptors

release pro-inflammatory cytokines to create inflammatory soup for healing (not usually nociceptive but activates silent receptors)

Hyperalgesia

increased response to pain, noxious stimuli elicits a greater response than normal

Hyperalgesia Physiology

decreased threshold for c-fibers

Allodynia

non-threatening stimuli begins to cause pain

Allodynia Wind up

c-fibers only maintain a state of partial depolarization, lay closer to threshold so easier to reach AP

Maladaptive nociception

prolonged inflammation leading to mechanical hyperalgesia and chronic pain

Spinal cord neuromodulation

afferent signals from non-noticeable stimuli jump onto nociceptive tracts due to SCI, brain interprets as noxious pain