Lecture 21 Flashcards
What can loss of pain sensation (due to nerve damage) be a feature of?
Diabetes mellitus and leprosy
How does pain differ from the classical senses?
It is both a discriminitive sensation and a graded motivation (or behavioral drive)
What is allodynia?
Sensitization to normally innocuous stimuli
What is hyperpathia?
Hysterical responses
What is specifity?
Theory holds that pain is a distinct sensation, detected and transmitted by specific receptors and pathways to distinct “pain areas” of the brain
What is convergence?
Theory suggests that pain is an integrated, plastic state represented by a pattern of convergent somatosensory activity within a distributed network (a so-called “neuromotion”)
How are afferents with free nerve endings (nociceptors?) classified?
Classified according to activating stimulus, fiber-type and conduction velocity
- lightly myelinated A-delta fibers, FAST 20 m/s
- mechanosensitive
- mechanothermal - sensitive
Nociceptors repond specifically to pain and are a subset of afferents with free nerve endigs. How is this easly demonstrated for?
Heat responses
i.e. Can find afferents whose activity correlates with pain perception
Clear that thermoreceptor activation has already saturated before pain is perceived
i.e. pain is not due to “ramping up” of normal receptors
What is Fast pain?
“first” pain
Sharp and immediate
Can be mimicked by direct stimulation of A-delta fiber nociceptors
What is Slow pain?
“second” pain
More delayed, diffuse and longer-lasting
Mimicked by stimulation of C fiber nociceptors
How can specifity be demonstrated?
Selectively blocking the fibers in turn
Which fiber is proprioceptive and which fiber is mechanoceptive?
A-delta
A-beta
What are molecular pain receptors?
Specific molecular receptors associated with nociceptive nerve endings are activated by heat (and hot chillis)
How are capsaicin receptors (TRPV1) activated?
Activated in nociceptive A-delta and C fibers at 45 degrees
Activated by capsaicin (a vanilloid which is the active component in chillis)
What are TRPV1 related other TRP receptors activated in?
A-delta fibers alone at even higher thresholds (52 degrees)
What are TRPs?
Respond directly to heat
What does capsaicin mimic?
Endogenous vanilloids released by stressed tissues
- nociceptors may also work by detecting release of chemicals from stressed cells
What are the two components of the central pain pathways?
- Sensory discriminative
- signals location, intensity and type of stimulus - Affective-motivational
- signals “unpleasantness”, and enables autonomic activation, classic fight-or-flight response
What tract does the discriminative pathway use?
Spinothalamic tract (also called anterolateral system) - pain goes through different pathways to reach different tissues
What do spinothalamic projections also preserve?
topography
What does the measurement of activity in the somatosensory cortex indicate?
- That this region does indeed respond to painful stimuli and that response correlates to intensity of pain
- Spatially mapped…
What does the comparison of cortical activation by painful (c fiber) or innocuous mechanical stimuli to skin demonstrate?
Painful stimuli activate the same region of the somatosensory cortex as the non-painful mechanical stimulation applied to the same region of skin
What does the activation of the insula and the cingulate cortex imply?
These regions are connected to the limbic system and known to be involved in the activation of emotional response
Part of the affective-motivational response to pain…
What does the affective-motivational pathways share some paths with?
Anterolateral (spinothalamic) system
