somatosensory function Flashcards
nociceptors: explain the physiological function of nociceptors
what does nociception provide, and what does the brain perceive this as
information about noxious (unpleasant or harmful) stimuli, which the brain perceives as pain
difference between nociceptive stimuli and pain
nociceptive stimuli can be measured, pain is subjective
suscpetibility of pain to contextual influences vs other modalities
pain is much more susceptible
where are nociception sensory neurone cell bodies
in peripheral nervous system (dorsal root ganglion for body or trigeminal ganglia for face)
what are the 2 nociception axon types
AB, C
what are AB nociception axon types used for, and features of transmission
mechano- or thermoreceptor; faster, produces sharp pain, leads to avoidance
what are C nociception axon types used for, and features of transmission
chemoreceptor (eg. bradykinin, histamine); produces dull aching pain, leads to guarding to allow recovery
size of nociception receptive fields
usually large
what is nociception intensity coded by
frequency of firing
basic central spinothalamic tract pathway: what is information conveyed via
VPL (ventral posterolateral) and VPM (ventral posteromedial) nuclei of thalamus
basic central spinothalamic tract pathway: where is information conveyed to and why
SI and SII cortex, for analysis of localisation and intensity of the noxious stimulus
collateral branches to brainstem of spinothalamic tract pathway: where is information conveyed to and why
forebrain structures, for perception of pain (afferent pathway)
collateral branches to periaqueductal grey of midrain of spinothalamic tract pathway: function
inhibit pain (central inhibition pathway)
in central spinothalamic pathway, where is somatotropic organisation maintained
through entire pathway from dermatomes to cortex
where does decussation of the pathway for information coming from the body occur
in spinal cord
where does decussation of the pathway for information coming from the head occur
in brainstem
afferent pain pathway (spinothalamic tract/spinal lemniscus) from face
face nociceptor-> primary sensory neurone -> through posterior pons down to medulla oblongata-> lateral synapse and decussation as secondary sensory neurone -> pass up through pons and midbrain -> thalamus -> tertiary sensory neurones -> somatosensory cortex
afferent pain pathway (spinothalamic tract/spinal lemniscus) from upper limbs
upper limb nociceptor -> primary sensory neurone -> posterior cervical cord-> synapse and decussation as secondary sensory neurone -> up spinothalamic tract through medulla oblongata, pons and midbrain -> thalamus -> tertiary sensory neurones -> somatosensory cortex
afferent pain pathway (spinothalamic tract/spinal lemniscus) from lower limbs
lower limb nociceptor -> primary sensory neurone -> posterior lumbar cord-> synapse and decussation as secondary sensory neurone -> up spinothalamic tract through medulla oblongata, pons and midbrain -> thalamus -> tertiary sensory neurones -> somatosensory cortex
where do spinothalamic tract axons send collateral branches to
brainstem (reticular formation), thalamus (intralaminar nuclei), hypothalamus and some cortex (e.g. cingulate gyrus, insula)
2 effects of axon collateral branches sent from spinothalamic tract
triggers increase in awareness, registers unpleasantness of stimulus i.e. pain
nociceptive dysfunction: effect of pathway disruption on pain and injury predisposition
may reduce pain, but predisposes to increased injury
nociceptive dysfunction: 3 changes which may exacerbate pain
windup in dorsal horn, thalamic syndrome, phantom pain
nociceptor fibres: Ad effect and stimuli (type 1 and type 2)
mediate sharp, intense or fast pain; type 1: noxious mechanical; type 2: noxious heat
nociceptor fibres: C fibres effect and stimuli
mediate dull, aching or second pain; noxious thermal, mechanicl and chemical stimuli
spinal cord nociceptive process: first synapse of pain pathway neurotransmitter
glutamate
sensory component of pain tract
lateral spinothalamic tract
emotional component of pain tract
spinoreticular tract (passes through parabrachial area)
functional MRI cerebral signature of pain: cortex
SI, SII, insula cortex, anterior cingulate cortex, prefrontal cortex
functional MRI cerebral signature of pain: other brain areas
amygdala, cerebellum, brainstem
nociceptive vs neuropathic pain
nociceptive: noxious stimulation of a nociceptor; neuropathic: lesion or disease of somatosensory system; can be mixed e.g. osteoarthritis and lower back pain
effect of peripheral sensitisation to pain (“inflammatory soup”)
decrease thresholds to peripheral stimuli at site of injury
3 effects of central sensitisation to pain (“inflammatory soup”)
decrease thresholds to peripheral stimuli at adjacent site of injury, expansion of receptive field, spontaneous pain
define hyperalgesia, with reference to primary and secondary; effect on normal pain response sigmoid curve
increased pain from stimulus that normally provokes pain (usually thermal or mechanical); primary occurs at area of injury or noxious chemical, secondary occurs around that primary area (shift to left vs normal pain response, at higher stimulus and pain intensity)
define allodynia; effect on normal pain response sigmoid curve
pain due to stimulus that does not normally invoke pain (shift to left vs normal pain response, at lower stimulus and pain intensity)
3 neuropathic pain sensory profiles
sensory loss, thermal hyperalgesia, mechanical hyperalgesia
descending control and chronic pain: inhibition vs facilitation endogenous drugs
inhibitory (protective): noradrenaline; facilitatory (harmful): serotonin
state of descending control in chronic pain patients
impaired
neuromodulation in chronic pain patients: what is done and how does it work
non-invasive primary motor cortex stimulation, activating endogenous analgesic systems in brain (periaqueductal grey and anterior cingulate cortex)
