sensory systems

Question 1

what does meissner’s corpuscle sense

Answer 1

light touch

Question 2

what does merkle’s corpuscle sense

Answer 2

touch

Question 3

what does paciniain corpuscle sense

Answer 3

deep pressure

Question 4

what does ruffini’s corpuscle sense

Answer 4

warmth

Question 5

sensory signal transduction

Answer 5

all sensory receptors transduce their adequate stimulus into a depolarisation
–> receptor (generator) potential

Question 6

what does receptor (generator) potential evoke

Answer 6

firing of action potentials for long distance transmission

Question 7

what does sensory signal transduction give info on

Answer 7

modality, intensity and location of stimulus

Question 8

primary afferent fibres: A-beta

Answer 8

touch, pressure, vibration

large, myelinate

Question 9

primary afferent fibres: A-delta

Answer 9

cold, fast pain, pressure

small myelinated

Question 10

primary afferent fibres: C

Answer 10

warmth, slow pain

unmyelinated

Question 11

which primary afferent fibres mediate proprioception

Answer 11

A-alpha and A-beta

muscle spindles, golgi tendon organs etc

Question 12

what do primary afferent fibres enter spinal cord via

Answer 12

dorsal root ganglia

or cranial nerve ganglia for head

Question 13

mechanoreceptive fibres

Answer 13

A-alpha
A-beta

project striaght up ipsilateral columns, synapse in cunate and graciel nucleu
2nd order fibres decussate in brainstem + project

Question 14

thermoreceptive + nociceptive fibres

Answer 14

A-delta
C

synapse in dorsal horn
2nd order fibres decussate in spinal cord
project up through contralateral spinothalamic tract

Question 15

damage to dorsal columns

Answer 15

loss touch, vibration, proprioception below lesion on ipsilateral side

Question 16

damage to anterolateral quadrant

Answer 16

loss of nociceptiev and temp sensation below lesion on contralateral side

Question 17

ultimate termination of sensory info

Answer 17

somatosensory cortex (S1) of poscentral gyrus

endings are grouped according to location of receptors –> sensory homunculus

Question 18

types of processing in sensory pathways

Answer 18

adaptation 
convergence
lateral inhibition 
not all info reaches brain 
perception

Question 19

convergence

Answer 19

saves on neurones
reduces acuity
underlies referred sensations

Question 20

lateral inhibition

Answer 20

activation one sensory fibre causes synaptic inhibition of its neighbours
gives better boundary definition, cleans up sensory info

Question 21

what are nociceptors activated by

Answer 21

low pH
heat
local chemical mediators: bradykinin, histamine, prostaglandins

Question 22

gate control theory of pain

Answer 22

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

Question 23

NSAIDs

Answer 23

NSAIDs are analgesics because they inhibit cyclo–oxygenase which converts arachindonic acid to prostaglandins

(prostaglandins sensitise nociceptors to bradykinin)

Question 24

local anaesthetics

Answer 24

block Na+ action potential and so all axonal transmission

Question 25

opiates

Answer 25

reduce sensitivity of nociceptors
block transmitter release in dorsal horn
activate desc inhibitory pathways