MODULE 5- Pain + Temperature Flashcards
nociceptors
unspecialized, nonspecific nerve endings that transmit a variety of stimuli + translate then into afferent APs
2 kinds of slowly transmitting afferent fibers
-Aδ (delta) lightly myelinated axons
-C unmyelinated axons, small diameter
pain is transmitted only when strength of stimulus is low/high
high
2 categories of pain
-faster conducting sharp FIRST PAIN carried by Aδ fibers
-delayed, broadly acting, dull SECOND PAIN carried by C fibers, which respond to all types of nociceptive stimuli
faster conducting sharp FIRST PAIN is carried by Aδ/C fibers
Aδ fibers
`
delayed, broadly acting, dull SECOND PAIN is carried by Aδ/C fibers
C fibers
2 types of Aδ fibers
-type 1
-type 2
type 1 Aδ fibers
-high heat thresholds
-respond to immediate potentially dangerous stimuli (e.g., pin prick)
type 2 Aδ fibers
-low heat threshold
-high threshold for mechanical stimulation
what does capsaicin activate
TRPV1 (VR-1)
-whose endogenous ligand is anandamide + temperature
where is capsaicin found
chili peppers, habanero, etc.
when is capsaicin an irritant
when applied to mucus membranes of the mouth + when injected subcutaneously
repeated administration of capsaicin leads to
desensitization
how is capsaicin clinically useful
as an analgesic + anti-inflammatory agent
central pain pathways (3)
-dorsolateral tract of Lissauer
-anterolateral system (AL)
-dorsal-column medial lemniscal system (DCML)
dorsolateral tract of Lissauer
ascending + descending branches of incoming afferent axons entering the dorsal horn
anterolateral system (AL)
formed from 2nd-order neuronal axons in the dorsal horn laminae I + V (wide dynamic range neurons)
-ascends carrying pain, temperature, + crude touch information to somatosensory cortex via the thalamus
dorsal-column medial lemniscal system (DCML)
carries mechanical stimuli
-touch, pressure, vibration, proprioception
AL + DCML systems are separate or together in the spinal cord
separate
where does the AL system decussate
at the point of entry into the spinal cord
where does the DCML system decussate
at the medulla
pain + temperature are ipsilateral/contralateral
contralateral
touch + pressure are ipsilateral/contralateral
ipsilateral
dermatomes
enable diagnosis of the location of the spinal cord injury
how is visceral (internal) pain transmitted
via dorsal horn neurons that also convey cutaneous pain
2 common examples of referred pain
-anginal pain arising because of inadequate blood flow in the heart is referred to the left arm + hand
-gall bladder pain referred to the scapular region
anginal pain arising because of inadequate blood flow in the heart is referred to
left arm + hand
gall bladder pain is referred to
scapular region
different aspects of pain are transmitted by ____ pain pathways
parallel
anterolateral system- sensory discriminitive
mediates location, intensity, quality of the noxious stimulus
sensory discriminitive information is conveyed from ____ to ____
anterior spinothalamic tract ->
ventral posterior lateral nucleus of thalamus
anterolateral system- affective motivational
unpleasant feelings, fear + anxiety
-autonomic reactions that accompany noxious responses, such as the sympathetic nervous system
pain matrix
extensive network of forebrain regions enabling one to experience the full range of pain
what does the pain matrix consist of
ventral posterior medial thalamus, somatosensory, insular, + anterior cingulate cortices
where does face pain originate
trigeminal (V) ganglion
-also from other ganglion associated with cranial nerves VII, IX, and X
peripheral mechanisms of sensitization
-CGRP
-NSAIDs
face pain climbs from ____ to ____
trigeminothalamic tract ->
ventral posterior medial thalamus
hyperalgesia
perception that pain is worse than it would normally be considered to be
peripheral sensitization
activated nociceptors stimulate the influx of non-neuronal cells (immune cells), neuropeptides + neurotransmitters, lipids, cytokines, + growth factors, all of which contribute to INFLAMMATION
purposes of sensitization (hyperalgesia, peripheral sensitization)
protect the injured area, promote healing, + ward off infection
pain is subjective/objective
subjective
hyperalgesia example
if you take a hot shower with a sunburn
how can hyperalgesia be initiated + maintained
by calcitonin gene-related peptide (CGRP)
what can be used to treat pain sensitivity
nonsteroid anti-inflammatory drugs (NSAIDs)
pathway for NSAIDs
inhibits cyclooxygenase ->
inhibits prostaglandin synthesis ->
reductoin in inflammation + pain
central mechanisms + treatments for sensitization
allodynia
allodynia
induction of pain by a normally innocuous stimulus
-caused by inadvertent stimulation of 2nd –order neurons in the dorsal horn that normally receive nociceptive inputs to give rise to a sensation of pain
phantom limbs + phantom pain
illusion that the missing limb is still present
-amputation -> functional reorganization of the somatotopic map in the primary somatosensory cortex
-usually feels like a burning/tingling sensation where the limb used to be
phantom limbs + pain are a common cause of
chronic pain syndrome
phantom limbs + phantom pain may be caused by
maladaptive plasticity in neural circuits representing sensations + actions of the body
reorganization of somatosensory cortex can cause
mapped cortical body parts to innervate contiguous (or adjacent) cortical areas, leading to misplaced feelings in the missing limb
-ex: stimulation of the left side of the face could lead to sensation that the left arm is being stimulated
ramachandran’s mirror box therapy
visual reality presents a contradiction to what the patient feels in the missing limb
-while viewing the intact limb + its relection/ movements, the patient superimposes the missing limb into the mirror-reversed intact limb
the placebo effect
a beneficial effect as a result of a pharmacologically inert “remedy”
placebo effect in postoperative patients can be blocked by ____
naloxone
imaging studies reveals that the placebo effect leads to
activation of opioid receptors in cortical + subcortical brain areas
-(e.g., anterior cingulate and insular cortices and amygdala)
example of placebo effect
saline injection gives people relief even though it is just saline
physiological basis of pain modulation- neurotransmitters used
wide variety of neurotransmitters used
-e.g., serotonin, dopamine, norepinpehrine
physiological basis of pain modulation- mediates the analgesic effects of what
periaquaductal gray (PAG)
physiological basis of pain modulation- what do descending projections to the dorsal horn do
balances excitatory and inhibitory interneurons
-plus the synaptic terminals of other descending pathways, to determine the efficiency of nociceptive transmission
physiological basis of pain modulation- interactions between what 2 things modulate the transmission of nociceptive information to higher centers
mechanoreceptor afferents + dorsal neural circuits
Melzack + Wall’s gate control theory of pain
concomitant activation of low-threshold mechanoreceptors can mitigate ascending nociceptive signals
ex: rubbing your finger that you accidentally hit with a hammer -> pain transmission
