sensory systems Flashcards
what does meissner’s corpuscle sense
light touch
what does merkle’s corpuscle sense
touch
what does paciniain corpuscle sense
deep pressure
what does ruffini’s corpuscle sense
warmth
sensory signal transduction
all sensory receptors transduce their adequate stimulus into a depolarisation
–> receptor (generator) potential
what does receptor (generator) potential evoke
firing of action potentials for long distance transmission
what does sensory signal transduction give info on
modality, intensity and location of stimulus
primary afferent fibres: A-beta
touch, pressure, vibration
large, myelinate
primary afferent fibres: A-delta
cold, fast pain, pressure
small myelinated
primary afferent fibres: C
warmth, slow pain
unmyelinated
which primary afferent fibres mediate proprioception
A-alpha and A-beta
muscle spindles, golgi tendon organs etc
what do primary afferent fibres enter spinal cord via
dorsal root ganglia
or cranial nerve ganglia for head
mechanoreceptive fibres
A-alpha
A-beta
project striaght up ipsilateral columns, synapse in cunate and graciel nucleu
2nd order fibres decussate in brainstem + project
thermoreceptive + nociceptive fibres
A-delta
C
synapse in dorsal horn
2nd order fibres decussate in spinal cord
project up through contralateral spinothalamic tract
damage to dorsal columns
loss touch, vibration, proprioception below lesion on ipsilateral side
damage to anterolateral quadrant
loss of nociceptiev and temp sensation below lesion on contralateral side
ultimate termination of sensory info
somatosensory cortex (S1) of poscentral gyrus
endings are grouped according to location of receptors –> sensory homunculus
types of processing in sensory pathways
adaptation convergence lateral inhibition not all info reaches brain perception
convergence
saves on neurones
reduces acuity
underlies referred sensations
lateral inhibition
activation one sensory fibre causes synaptic inhibition of its neighbours
gives better boundary definition, cleans up sensory info
what are nociceptors activated by
low pH
heat
local chemical mediators: bradykinin, histamine, prostaglandins
gate control theory of pain
acitivy of A-alpha/beta fibres activate inhibitory interneurones which release endorphines which inhibit transmitter release from A-delta/C fibres
same inhibitory pathways are activated from desc pathways from peri-aqueductal grey matter and nucleus raphe magnus
NSAIDs
NSAIDs are analgesics because they inhibit cyclo–oxygenase which converts arachindonic acid to prostaglandins
(prostaglandins sensitise nociceptors to bradykinin)
local anaesthetics
block Na+ action potential and so all axonal transmission
opiates
reduce sensitivity of nociceptors
block transmitter release in dorsal horn
activate desc inhibitory pathways
