Sensory Systems and the pathophysiology of pain Flashcards
nociceptors respond to
pain/ damaging stimulus
two types of receptors
physiological (sensory)
pharmacological (protein)
all sensory receptors TRANSDUCE their adequate stimulus into a depolarisation called the
receptor potential
the size of the receptor potential encodes the
intensity of the stimulus
receptor potential evokes what?
AP firing
the frequency of AP firing also encodes for the
intensity of the stimulus
receptive field encodes the
location of the stimulus
APs are transmitted to the CNS via
axons
cutaenous sensation is mediated by what 3 types of primary afferent fibres?
large myelinated
small myelinated
unmyelinated
unmyelinated fibres detect
warmth and ‘slow’ pain
small myelinated fibres detect
‘fast’ pain and pressure
large myelinated fibres detect
touch, pressure and vibration
the transmission of sensory information is via what three types of fibres?
mechanoreceptors
thermoreceptors
nocireceptors
afferent neuron from pain and temperature (nocireceptive and thermoreceptive) travel up what?
the contralateral spinothalamic tract
receptors for body movement, limb positions, fine touch discrimination and pressure (mechanoreceptors) all travel up via what?
dorsal column
damage to dorsal columns causes loss of
touch
vibration
proprioception
(below lesion on ipsilateral side)
damage to the anterolateral (contralateral spinothalamic) tract causes of loss
nociceptive and temperature sensation below lesion on contralateral side
signal transduction in nociceptors is activated by
low pH
heat
local chemical mediators (bradykinin, histamine, prostaglandins)
what is gate control theory?
non-painful input closes the nerves ‘gates’ to painful input, which prevents pain sensation from traveling to the CNS
activity of Aalpha/beta fibres activates what in gate theory?
inhibitory interneurons
inhibitory interneurons release opioid peptides (endorphins) that inhibit
transmitter release
‘closing the gate’
local anaesthetics block Na+ and therefore
block APs and axonal transmission
NSAIDs - basically block the production of
prostaglandins
so work well against pain associated with inflammation
prostaglandins act on voltage gated sodium channels to allow for
depolarisation
and therefore AP firing
opiates do what 2 things to stop pain
reduce sensitivity of nociceptors
block transmitter release in the dorsal horn
activate descending inhibitory pathways
what is nociception?
the detection of tissue damage by A delta and C fibres
C fibres are myelinated or unmyelinated?
unmyelinated
Dorsal column carries what kind of signals?
Aalpha or Abeta axons
non-nociceptive mechanoreceptors
the spinothalamic tract is the major ascending tract for
nociception
what is central sensitisation?
the response of 2nd order neurons in the CNS to normal input both noxious and non-noxious
(noxious = painful/harmful)
what is nociceptive pain?
a sensory experience that occurs when specific peripheral sensory neurons (nociceptors) respond to noxious stimuli
what is neuropathic pain?
pain initiated or caused by a primary lesion or dysfunction in the somato-sensory system
what are the 3 main components of central sensitization?
wind up
classical
long term potentiation
wind up only takes place in
activated synapses
classical involves the
opening up of new synapses
long term potentiation involves mainly the
activated synapses (for intense stimuli)
