Lecture 3 Part 2: Pain Flashcards
what are the 3 types of pain
acute
chronic
referred
what is acute pain
Clearly defined stimulus that determines the intensity and duration of pain
localized receptors (afferents) are affected
what is the function of acute pain?
Detect tissue damage or impending damage; initiate
avoidance reaction
what is chronic pain
Persistence of pain, often in absence of obvious stimulus
Cause & mechanisms are largely unknown so it’s difficult to treat
often involves changes in pain pathways
what is referred pain?
pain caused in one body part but felt in another area
why do we have referred pain?
Very few neurons in the dorsal horn of the spinal cord are specialized for transmission of visceral (internal) pain
what are the 3 ways that pain receptors similar to mechanoreceptors
arise from DRG
Transduce a variety of stimuli that trigger action potentials
frequency rate coding (more stimulus intensity more depolarization and more firing rate of pain afferents
what are the 4 ways pain (nociception) is different from somatosensation (touch)
Specialized for damaging (nociceptive) stimulation
Information travels much more slowly
Localization is relatively poor
Repeated or prolonged stimulation often leads to a stronger response (sensitization), rather than adaptation
what are the 4 specializations of nociceptors?
mechano-nociceptors (intense force)
thermo-nociceptors
chemo-nociceptors
nonspecific (respond to more than one type of stimuli)
does the perception of pain (nociception) depend on specifically dedicated receptors and pathways or excessive stimulation of the same receptors that generate other somatic sensations?
specifically dedicated receptors and pathways
what are the 2 types of fibers that carry from the free nerve endings
alpha delta (myelinated. but still slower than somatosensation)
c fibres (unmyelintated)
why is localization poor with nociception
there’s large receptive fields with more branching
what are the two aspects of pain
sensory-discriminative: (spinothalamic tract> VPL/VPM in thalamus > primary sensory cortex
affective-motivational: spinothalamic tract > anterior nuclear group in thalamus > insular cortex
what does the Sensory-Discriminative aspect tell us
location and intensity of pain
what does the Affective-Motivational aspect of pain tell us
Unpleasantness of Pain & anxiety
Autonomic activation (fight or flight)
how do the Sensory-Discriminative and Affective-Motivational aspects of pain differ
they go to different places in the thalamus
what is gate control theory?
non nocecptibe info from rubbing hand inhibits pain information or spinothalamic tract which stops the pain from going up into the thalamus
what is the endogenous opioid theory?
natural occuring pain killers that brain sends down to spinal cord to stop pain transmission
what is peripheral sensitization?
Interaction of nociceptors with ‘inflammatory soup’ of substances released due to tissue damage
swelling area around site of damage more susceptible to pain called hyperalgesia
what is central sensitization?
Allodynia (painful sensation to non-painful stimuli) outside zone of terminal branching (of nociceptors) – not due to peripheral mechanisms – must be centrally mediated
why does allodynia happen?
High excitability in dorsal horn
Activity levels in nociceptive afferents that were subthreshold prior to the sensitizing event become sufficient to generate action potentials in dorsal horn neurons, contributing to an increase in pain sensitivity
what causes neuropathic pain
Damage to nerve structures themselves
is pain just a sensory system
no it also activates motivational parts of the CNS
Central sensitization - the perception of pain in response to non-noxious stimuli - is attributable to all of the following except:
-Increased synaptic strength in the dorsal horn
-Release of substance P and histamine from nociceptive afferent terminals
-Progressive increase in the discharge rate of dorsal horn neurons
-Enhancement of postsynaptic potentials from ‘LTP-like’ mechanisms
Increased synaptic strength in the dorsal horn
Nociception and tactile sensation have some similar functional properties. Which of the following statements does NOT reflect a similarity between painful and non-painful afferents?:
Lack of spontaneous activity
Frequency coding
Transduction speed
Transduction mechanism
Transduction speed
true or false:
Central sensitization, including vasodilation and hyperalgesia of the skin surrounding the site of damage, results in part from a decrease in the threshold for discharge of local nociceptors.
false
why can visceral pain be perceived as a pain at a site other than its actual source
It is transmitted with cutaneous afferents from various dermatomes in the dorsal horn
true or false:
The pulvinar and mediodorsal nuclei of the thalamus synapse directly with the sensory cortex as part of the emotional/affective pain pathway
false
true or false:
Somatosensation is a faster process than nociception.
true
true or false:
Endogenous opioids modifies the activity of C-polymodal fibres by decreasing their ability to transmit pain ‘signals’ to the sensory cortex.
true
