Pain - Tom Salomon Flashcards
What is pain
unpleasant sensory and emotional experience due to actual or potential tissue damage or described in terms of such pain
why is pain good
guides behaviour by signalling harm to our bodies - learn how to avoid injury
What are melzachs 3 forms of pain
short term - ie reflexive withdrawal from a stimulus
long term - ie promotion of recuperative behaviours
expression - social signalling to others of potential harm and to elicit caregiving behaviours
what is a bottom up theory of pain
pain determines by the properties of the stimulus and teh receptor that encodes it
what is specificity theory
stimulus activates fibres that sends message to the brain - specific fibres, pathways and brain regions associated with specific pain
types of specific receptors
parcinian corpuscles
meisseners corpuscles
merkels discs
ruffinis corpuscles
what are nociceptors
pain receptors with free nerve endings that response to nocious stimuli that could lead to tissue damage
types of nociceptors
a delta
c fibre
define a delta nociceptors
low threshold, thick and myelinated for fast conduction of info for initial fast sharp localised pain
define c fibre nociceptors
high threshold thing unmyelinated receptors for slow conductance of diffuse pain ie burning
describe the spinothalamic tract (highter order path)
A delta/c fibre decussate at dorsal horn of spinal cord
Ascend to contra lateral thalamus
Ascend to somatosensory cortex and periacqueductal gray PAG
describe spinoreticular tract (higher order path)
A delta and c fibre decussate at dorsal horn
ascend to reticular formation at brain stem
Ascend to intralaminar nuclei of thalamus and hypothalamus
problems with bottom up theories
peripheral input not account for variety of pain experienced
i.e. why ovverride when distracted, how alter via placebo and percieved control influence
Invariable link between pain and injury - pain but no injury ie phantom limb or injury without pain ie episodic/congenital analgesia
define episodic analgesia
absence of pain in response to pain stimuli
define congenital analgesia
no sensation of physical pain from stimuli from birth
define melzack and wall gate control theory
Inhibitory pain modulation at the spinal cord level - explain why when we bang our head, it feels better when we rub it.
activating A fibres with tactile, non-noxious stimuli, inhibitory interneurones “gate” in the dorsal horn are activated leading to inhibition of pain signals transmitted via C fibres
describe periacquductal gray
PAG in midbrain and rostral ventromedial medulla (RVM) - involved in descending inhibitory modulation. centres contain high concentrations of opioid receptors and endogenous opioids - analgesic(pain relief). Descending pathways project to the dorsal horn and inhibit pain transmission & modulate emotion ie defence and fear responses
describe rostral ventromedial medulla
strong connection to PAG
projects heavily to dorsal horn
forms part of a descending pathway that modulates nociceptive neurotransmission at the dorsal horn
3 categories of neurons:
On-cells, off-cells, and neutral cells. Off-cells decrease in firing rate right before a nociceptive reflex - inhibitory
On-cells activity immediately preceding nociceptive input - excitatory.
Neutral cells no response to nociceptive input.
Increase/decrease in perception of pain
what is the pain matrix (apkarian et al 2005)
meta analysis of brain regions active across modalities during experience of pain
indicated cortical and subcortical substrates underlying pain perception and network of somatosensory, limbic and associated structures recieving nociceptive input
Areas directly involved in the pain matrix
Primary & secondary somatosensory cortex
Insula
Anterior cingulate cortex
Prefrontal cortex
Thalamus
what is secondary hyperalgesia
increased sensitivity to pain due to nococeptive damage outside of the main injury site - heightened pain response to stimuli as a measure of central sensitisation and role in descending modulatory system ie activity of RVM
testing secondary hyperalgesia
expose pps to thermal stimuli and measure SH before and after
one group given pain relevant CBT and the other psychotherapeutic intervention
intensity remains tehsame but resuction in way pain is viewed in CBTgrou
+ sig reduction in SH sensitivity - mind over matter
how does the brain modulate pain
reduced pain assoc with reduced response in accumbens and insula
regulation of pain activates preganule acc, vmPFC, vl/dlPFC (emotional regulation involvement)
salomons et al 2004 perceieved control and pain
response to pain depend on peripheral nociceptive input as well as cog and affective context - degree pain is percieved as controllable
manipulate belief - tell reduce stimulus to non painful duration if respond in correct direction and response less than threshold response
findings of salomons et al 2004
regions involved in pain sensitive to cog context - reduced sensitisation when thought to be in control of stimulus intensity
vmPFC active only when pain uncontrollable - not primary but thought to modulate
overlap between acc and insula
dl/vl 65% variation in pain rate - high involvement in pain modulation
Melzach and cadet dimensions of pain
Sensory discriminative
Motivational affective
Cognitive evaluative
Melzach and cadet sensory discriminative define
info of intensity, location or quality ie throbbing
Melzach and casey motivational affective define
emotional component that determines avoidance of a stimulus ie sickening
Melzach and casey cognitive evaluative define
evauation of the meaning/context ie mild or excrutiating pain
Spinothallamic tract linked to
Pain localisation
What is the spinoreticular pathway linked to
Emotional/feeling aspect of pain
Areas thought to be involved in pain and pain modulation
Hippocampus
Brain stem
Amygdala
PAG/RVM
Basal ganglia
Posterior partial cortex
Types of cortical responses in pain modulation
Altered pain matrix responses
Activation of pain modulation regions
What areas in pain matrix alter response to modulation
ACC
insula
(Reduction in activity)
What areas in brain activate in pain modulation
Vl/dl/vmPFC
pregenual ACC
Pain matrix activation in pain modulation - evidence
ACC activate when subjects distracted by task
Salomons
Perceived control reduces
Descending Cortical modulation areas activity
Perceived control - Activation of vlPFC vmPFC and PAG
Placebo analgesia (perceive analgesic effect because believe they will) - vmPFC dlPFC and PAG
Attention to pain - vmPFC and PAG
Diabetic encephalitis patient emotional response to pain
lesions to ACC amygdala and insula (involved in experience and modulation of pain)
Capable of experiencing pain despite no regions
Can modulate pain based on meaning to him
Social pain problem
Media makes quick inferences about studies into pain and make incorrect judgements about how to treat etc
Reverse inferences
Define reverse inference
Logical error by affirming the consequent - perceive that activation leads to pain when not necessarily true
Mouraux reverse inference
Does pain matrix activation mean feel pain
NO
Same areas also activate for non painful sensory stimuli ie tactile auditory or visual
