sensory systems including pain Flashcards
what is each type of sensory information associated with?
a specific receptor type responding to a specific sensory modality
what is the receptive field?
the specific area over which a sensory receptor will respond to a stimulus
what does a meissners corpuscle sense?
light touch
what does a merkles corpuscle sense?
touch
what does a free nerve ending sense?
pain
what does a pacinian corpuscle sense?
deep pressure
what does a ruffini corpuscle sense?
warmth
what do all sensory receptors do to their adequate stimuli?
transduce them into depolarisation - which is the generator potential
what encodes the intensity of a stimulus?
the size of the receptor potential
what does the receptor potential evoke?
firing of action potentials for long distance transmission
what does the frequency of action potentials encode?
intensity of stimulus
what determines the acuity of a stimulus?
density of innervation and size of receptive field
what 3 types of primary afferent fibres mediate cutaneous sensation?
large myelinated fibres
small myelinated fibres
unmyelinated fibres
what type of information do large myelinated fibres convey?
touch
pressure
vibration
what type of information do small myelinated fibres convey?
cold
fast pain
pressure
what type of information do unmyelinated fibres conve/y
warmth
slow pain
what fibres mediate proprioception?
2 types - large myleinated and A alpha
where do all afferent fibre types enter the spinal cord?
via the dorsal root ganglia (or cranial nerve ganglia for head)
how do mechanoreceptive (large myelinated) fibres project to the brain?
through ipsilateral dorsal columns
where do the mechanoreceptive fibres decussate?
brainstem
where do the mechanoreceptive fibres synapse?
in the cuneate and gracile nuclei
where do mechanoreceptive fibres project to after they decussate?
thalamus, reticular formation and cortex
where do the thermoreceptive and nociceptive fibres (short myelinated and unmyelinated)synapse?
dorsal horn
where do the thermoreceptive and nociceptive fibres decussate?
in the spinal cord
how do the mechanoreceptive and nociceptive fibres project to the brain?
through the controlateral spinothalamic tract
where do the mechanoreceptive and nociceptive fibres project to within the brain?
thalamus, reticular formation and cortex
what is the result of damage to the dorsal column?
loss of touch
vibration
proproception below the lesion on the IPSILATERAL side
what is the result of damage to the anterolateral quadrant (spinothalamic)
causes loss of nociceptive and temperature sensation below the lesion on the contralateral side
where is the ultimate termination point for sensory signals?
somatosensory cortex of the post central gyrus
how are the nerve ending grouped in the post central gyrus?
according to the location of the receptors
what are 3 ways that help process information in sensory pathways?
adaptation
convergence
lateral inhibition
what is convergence?
when different neurones synapse in the same place?
what are some of the effects of convergence?
saves on neurones
reduces acuity
may underlie referred pain
what is lateral inhibition?
when activation of one sensory input causes synaptic inhibition of its neighbours
what is the effect of lateral inhibition?
gives better definition of receptive field boundaries
cleans up sensory information
what can activate signal transduction in nociceptors?
low pH, Heat
local chemical mediators (bradykinin, histamine, prostaglandins)
in the gate control theory of pain, what do inhibitory interneurones release?
opioid peptides which inhibit transmitter release from pain fibres
what can activate inhibitory interneurones in the gate control theory?
mechanoreceptive fibres
nucleus raphe magnus
pari-aqueductal grey matter
how are NSAIDS analgesic?
they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglanidins (prostaglandins sensitise nociceptors to bradykinin)
how are local anaesthetics analgesic?
they block the Na+ action potential and therefore block all axonal transmission
how are opiates analgesic?
they reduce the sensitivity of nociceptors
block transmitter release in the dorsal horn
and they activate descending inhibitory pathways
