BMS11004 WEEK 11 - TUESDAY Flashcards
pain, nociceptors, afferent fibres, tracts
define specificity theory
pain is a distinct sensation, detected/transmitted by specific receptors to distinct brain area
define convergence theory
pain is integrated, plastic state represented by pattern of convergent somatosensory activity within distributed network (neuromatrix)
what type of fibre (a, b, y) are lightly myelinated nociceptors, what modality are they, how fast
Aδ (alpha delta)
fast (20m/s)
mechanosensitive, mechanothermal-sensitive
what type of fibre (a, b, y) are unmyelinated nociceptors, what modality are they, how fast
C fibre
slow (2m/s)
polymodal= mechanical, thermal, chemical
when are nociceptors most easily demonstrated
in heat response- find afferent whose activity correlate with pain perception
what fibre types mediates fast pain
sharp, immediate
mimicked by direct stimulation of Aδ (delta) fibre nociceptors
what fibre types mediates slow pain
diffuse, delayed, long-lasting
mimicked by stimulating C fibre nociceptors
when you cut yourself, what nociceptors activate
first sharp pain = Aδ
replaced by long dull pain = C fibres
what are molecular pain receptors
specific molecular receptors associated with nociceptive nerve endings and activated by heat, hot chillis
capsaicin receptor (TRPV1) is a specific molecular receptor. describe what fibres it is activated in, how
activated in nociceptive Aδ and C fibres at 45c by capsaicin (vanilloid, active component in chilli)
name the 2 ways that molecular receptors can respond in pain
responds to heat directly and fire
capaicin can bind and cause it to fibre
name the 2 components of central pain pathways
sensory discriminative - signals location, intensity, stimulus type (involve spinothalamic tract)
affective motivational- signal unpleasant, enables fight/flight autonomic response
what is spinothalamic tract also known as
anterolateral system
explain topological maps of pain
topologically represented in cortex, region responding to painful stimulus and response correlates to pain intensities
explain what brain areas are linked to affective-motivational response to pain
insula, cingulate cortex (limbic system)
explain topographical maps of affective-motivational pathway, and locations
little mapping
share pathways with anterolateral system
neurons in paracrachial nucleus respond from any body surfaces
what is hyperalgesia
increased response to painful stimuli (hypersensitivity of damaged skin to normally tolerable pain stimulus eg: pin prick)
what is allodynia
painful response to normally innocuous stimulus (painful sensitivty of subburnt skin to brush)
what is hyperalgesia due to, and peripheral effects
lowered nociceptor threshold
damaged tissue releases inflammatory substances, affecting nerve function, attract mast cell, neutrophils, increase blood flow
what are prostaglandins (inflammatory response in hyperalgesia)
lower threshold for AP generation
in analgesic painkillers
what is hyperpathia
variant of hyperalgesia/allodynia
due to fibre/axonal loss/damage
cause raised detection threshold, when exceeded causes explosive pain
can occur when central pathway damaged- shingles, diabeters, MS, stroke
when is neuropathic pain experienced
post amptutation
what can phantom limb pain suggest regarding central representations
illusion of limb being present
suggest central representation of body isnt passive, and occur when born without limb suggesting central map pre-formed
what is referred pain
due to damage in viscera, perceived as coming from specific location according to location of organ eg: heart attack in shoulder
reflect convergence of visceral afferent onto pathway as cutaneous afferent in CNS
useful in clinical diagnosis
what does stimulation of PAG do
activates brainstem nuclei modulating activity in dorsal horn neurons
activating enkephalin releasing interneurons, presynaptically inhibiting nociceptive fibres
why does rubbing injury (modulation) work
locally inhibit mechanoreceptive (A-beta fibres) of nociceptive (C fibres) in spinal cord
suggests pain perception due to integration of convergent sensory info
