Acute and Chronic Pain Flashcards
analgesia
absence of spontaneous report of pain or pain behaviors in response to stimulus normally expected to be painful
dysesthesia
and unpleasant abnormal sensation, whether spontaneous or evoked
hyperesthesia
increased sensitivity to stimulation, excluding special senses
hypoalgesia
diminished pain in response to a normally painful stimulus
neuropathic pain
pain arising as a direct consequence of a lesion or disease affecting the somatosensory system
nociceptor
a receptor preferentially sensitive to tissue or trauma or to a stimulus that would damage tissue if prolonged
nocioception
activation of sensory transduction in nerves by thermal, mechanical, or chemical energy impinging on specialized nerve endings
plasticity
nociceptive input leading to structural and functional changes that may cause altered perceptual processing and contribute to pain chronicity
What is the gate control theory?
an modulate pain at the spinal chord
Rubbing of large fibers will gate pain fibers at the spinal cord
highlights the importance of the spinal cord dorsal horn in modulating increasing pain signals, can be gated to eliminate pain signal from C-fibers
Descending pathways are also involved
three components: sensory, affective, evaluative
What is the neuromatrix theory?
individuals develop their own “neurosignature” as part of a neural netowrk which is influenced by a number of inputs (previous physical or psychological trauma), genetic susceptibility, cognitive and evaluative, that feed into a network of brain structures in creatin g”outputs” over time in one’s life manifesting as pain, one’s action program, and long term effects on the stress regulation or endocrine system
updated Gate Control Theory
transduction
detection of noxious or damaging stimuli
this signal is transduced into electrical activity by various types of nociceptors
thermal nociceptors detect extreme temperatures, chemical nociceptors detect noxious substances, and mechanical nociceptors detect high-intensity pressure
conduction
detection of noxious or damaging stimuli
resulting electrical signals are conducted via primary afferent nociceptive neurons to the dorsal horn of the spinal cord
transmission
synaptic transfer of input to neurons with specific laminae of DH
two ascending pathways - spinothalamic and spinoparabrachial tracts
spinothalamic tract relays through the thalamus to the somatosensory cortex and related areas
modulation
the sensation of pain and the response to pain are affected not only by pain transmission from affected neurons (via ascending pathways) but also by the brain’s response to that transmission (via the descending pathways)
inhibitory spinal interneurons and projections from the brainstem to the dorsal horn of the spinal cord modulate pain signaling by limiting the transfer of incoming snesory input to the brain
perception
the spinothalamic tract relays pain information through the thalamus to th esomatosensory cortex and associated areas, allowing for localization of pain, avoidance behavior, and cognitive processing of pain
affective response
the spinoparabrachial tract relays the pain stimulus to the parabrachial nucleus of the brainstem, continuing on to the ventral medial nucleus of the hippocampus and the central nucleus of the amyglada, brain regions involved in the affective response to pain
allodynia
a pain due to astimulus which does not normally provoke pain.
Temperature or physical stimuli can provoke allodynia, (which may feel like a burning sensation), and it often occurs after injury to a site.
hyperalgesia
an increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves
what is normally painful becomes much more painful
What are the outcomes of healing to injury with plasticity?
hyperalgesia and allodynia
will lead to chronic pain
What are Abeta fibers?
large, thickly myelinated fibers that are non-nocioceptive
- normally responds to non-painful (mechanical) stimuli
- can be recruited into pain processing over time
What are Adelta fibers?
small, thinly myelinated nociceptive fibers
- respond to heat, cold, and high-intensity mechanical stimuli
What are C fibers?
unmyelinated, nociceptive fibers
responds to head, mechanical, and chemical stimuli
What is the response for non-painful stimuli?
specificity for a particular stimulus
high degree of gain to amplify weak signals
rapid adaptation to increasing intensities
What is the response for painful stimuli?
specificity is less important
high threshold receptors - thermal, chemical, and mechanical stimuli (polymodal)
threshold for firing may decrease
What is the framework for acute/subacute injuries?
clinical alterations - symptoms
anatomical alterations - tissue injuries and overload
functional alterations - biomechanical deficits and subclinical adaptations
What are the clinical symptoms of musculotendinous overload?
pain
instability
dysfunction
What are functional biomechanical deficits of musculotendinous overload?
muscular weakness
inflexibility
scar tissue
muscle strength imbalance
What is the signaling cascade in peripheral nerve terminals?
chemical, mechanical, or thermal activation of peripheral nociceptors via nonselective cation or Na+ channels
influx of calcium and sodium ions depolarizes the membrane
voltage-gated sodium channels open and further depolarize the membrane
burst of action potentials
What are the key neurotransmitters and modulators involved in pain processing?
increased processing: glutamate and substance P
decreased processing: norepinephrine, serotonin, GABA, glycine, endocannabinoids, endorphins, monoamines
What are the features of central sensitization?
development of or increases in spontaneous neural activity
reduced threshold for activation by peripheral stimuli or for dorsal horn neural activation
increased receptive field of nociceptive afferents or dorsal horn neurons
increased response of dorsal horn neurons to painful stimuli
What are the potential mechanisms for central sensitization?
cellular processes such as decreased inhibition, increased membrane excitability, and synaptic facilitation
microglial activation
What are some of the effectors altered in central sensitization?
changes in threshold and activation kinetics of NMDA and AMPA receptors
changes in AMPA receptor membrane trafficking
alterations in ion channels to increase inward currents and reduce outward currents
reductions in the release or activity of GABA and glycine
altered gene expression in dorsal horn neurons
What is the function of calcium channels in the nervous system? What are drugs that modify its function?
inward channel, primary driver for most intracellular responses to stimulation
drugs: pregabalin, gabapentin, ziconotide
What is the function of potassium channels in the nervous system? What are drugs that modify its function?
outward channels - efflux of potassium makes the membrane potential more negative (hyperpolarized)
drugs: baclofen, clonidine, opioids
What is the function of sodium channels in the nervous system? What are drugs that modify its function?
inward channel - influx of sodium through open channels makes membrane potential less negative, bringing it closer to the threshold potential necessary to initiate an action potential
drugs: local anesthetics, carbamazepine, phenytoin
What is the function of chloride channels in the nervous system? What are drugs that modify its function?
inward channel: influx of chloride makes the membrane potential more negative (hyperpolarized)
drugs: benzodiazepines (amplify GABA, induced opening of channel)
What are the key steps in pain mechanisms?
sensitization and abnormal peripheral input
leads to…
sensitization and amplification of peripheral input in the dorsal horn
leads to…
sensitization of neuron in the brain
What are the mechanisms of nocioceptive central pain?
autosensitization of receptors
ectopic firing of dorsal root ganglion cell
calcium-induced molecular cascades from excess glutamate
phenotypic change of A-ß cells and DRG
changes in gene expression of sodium channels and neuropeptides
anatomic changse at dorsal horn
Where is pain processed?
center just for pain: thalamus
center for pain and emotion: somatosensory cortex, insular cortex, hippocampus, amyglada, anterior cingulate cortex
What is catastrophizing?
definition: exaggerated negative orientation toward a noxious stimulus
rumination - “I can’t seem to get it out of my mind”
magnification - “I become afraid that the pain will get worse”
helplessness - “I feel I can’t stand it anymore”
What is Gatchel’s 3-stage model for acute to chronic pain?
state I - normal emotional reaction during acute phase
stage II - behavioral and psychological reactions and problems
stage III - acceptance or habituation to “sick role”
What are the symptoms of central sensitization?
hyperalgesia
spontaneous pain
allodynia
decreased threshold to peripheral stimuli
expansion of receptive field
increased spontaneous activity
What are the features of muscle pain?
aching and cramping
difficult to localize and refers to other deep somatice tissues (fascia, muscles, joints)
muscle nocioceptive activity is processed differently in the CNS
inhibited more strongly by descending pain-modulating pathways than cutaneous pain
What is myofascial pain?
characterized by regional areas of muscle weakness or dysfunction many times associated with an area of acute or chronic injury that has characteristic referral patterns of pain, many times mimicking a “pinched nerve” or radicular spine syndrome
symptoms of myofascial pain
local and referred pain
pain with iso contraction
stiffness, limited ROM
muscle weakness
paresthesia and numbness
propioceptive disturbance
autonomic dysfunction
What are the physical findings of myofascial pain?
local tenderness
single or multiple muscles
palpable nodules
firm or taut bands
“twitch response” (LTR)
jump sign
muscle shortening
limited joint motion
muscle weakness
What are some causes of chronic pain?
trauma
congenital or familial abnormalities
nerve or nervous system injury
osteoarthritis
muscle or visceral injury
other systemic disorders where pain continues to persist for at least 3 to 6 months with characteristic central or peripheral nervous system changes
What is the treatment for chronic pain?
relies on pharmacologic therapies to help reduce pain, improve mood, improve sleep quality, and return patients to previous lesure activities and work
What are teh characteristics of organ pain?
the viscera have lower densities of sensory nerve innervation and share sympathetic and parasympathetic convergence in the central nervous system
visceral or organ pain is usually more poorly localized
