Sensory Systems

Question 1

a stronger stimulus will give a greater amplitude or frequency

Answer 1

greater frequency

Question 2

a longer stimulus will give greater length of signal or greater frequency

Answer 2

greater length

Question 3

which primary afferent fibres signal is fastest

Answer 3

a-beta -thickest and myelinated

Question 4

what do a-beta fibres receive

Answer 4

touch, pressure, vibration and proprioception

Question 5

what do a-delta fibres receive

Answer 5

cold, fast pain and pressure

Question 6

what do c fibres receive

Answer 6

warmth and slow pain

Question 7

which of the 3 fibre types is the biggest and most myelinated

Answer 7

a-beta (hence fastest signal)

Question 8

which fibre is unmyelinated

Answer 8

c fibres (hence slowest signal)

Question 9

which two types mediate pressure

Answer 9

a-delta and a-beta

Question 10

which two types mediate proprioception

Answer 10

a-alpha and a-beta

Question 11

what is the dorsal root ganglion equivalent in the head

Answer 11

cranial nerve ganglia (nuclei)

Question 12

the area a nerve is responsive to stimulus over is its _______ field

Answer 12

receptive

Question 13

a nerve will _____ to send a AP

Answer 13

depolarise

Question 14

a deeper receptor is more/less accurate

Answer 14

less accurate

Question 15

what are the 3 types of primary afferent fibres of cutaneous sensation

Answer 15

A-beta, A-delta and C

Question 16

what are the 2 types of primary afferent fibres of proprioceptin

Answer 16

A-alpha and A-beta

Question 17

what types of sensory nerves that we know about are A-alpha or A-beta

Answer 17

muscle spindles and golgi tendons as in stretch and inverse stretch reflexes

Question 18

afferent fibres of pain

Answer 18

A-delta and C fibres

Question 19

how do all primary afferent fibres enter the spinal cord

Answer 19

through the dorsal root ganglion (or cranial nerve ganglia in head)

Question 20

how do A-alpha and A-beta fibres travel up the spinal cord

Answer 20

they go up the dorsal column, synapse with 2nd order which then cross the midline and project up to the thalamus and so on

Question 21

how do A-delta and C fibres travel up the spinal cord

Answer 21

they are thermo and nociceotive so they synapse and cross over at entry and travel in the spinothalamic tract

Question 22

where does all the sensory information terminate

Answer 22

somatosensory cortex (postcentral gyrus)

Question 23

what happens when a stimulus is held for a long time

Answer 23

they APs stop. they will fire again when the stimulus is removed (like wearing clothes)

Question 24

what pathway feature may explain referred pain

Answer 24

convergence

Question 25

convergence increases/reduces acuity

Answer 25

reduces

Question 26

when you touch an area of skin what is the effect on the surround nerve endings that are not being touched

Answer 26

they receive lateral inhibition

Question 27

benefit of lateral inhibition

Answer 27

gives a sharper cleaner sensory image and borders are more defined

Question 28

explain the gate control theory of pain

Answer 28

when A-alpha/beta neurons are excited and enter the spinal cord they stimulate inhibitory interneurones that release opioids (endorphins) to act on the A-delta/C neurones when the original signals reach the midbrain this inhibition is further stimulated

Question 29

effect of prostaglandins on bradykinin and thus on pain

Answer 29

prostaglandins sensitise nociceptors to bradykinin. bradykinin is released in response to noxious stimuli which stimulates nociceptors. prostaglandins therefore help pain signals be sent

Question 30

when is bradykinin released

Answer 30

when there is a noxious stimulus

Question 31

how do NSAIDs work to block pain

Answer 31

they inhibit cyclo-oxygenase enzyme (which generates prostaglandins) and so desensitise the nociceptor to bradykinin

Question 32

local anaesthetic block which electrolyte responsible for action potentials

Answer 32

Na+ - all axonal transmission is blocked

Question 33

how does TENS work

Answer 33

it stimulates mechanoreceptors at same level as pain and so stimulates the inhibitory opioid pathways blocking 1st to 2nd order neuron synapse

Question 34

what class of analgesics activate descending inhibitory pathways

Answer 34

opiates e.g. morphine

Question 35

what class of analgesics blocks transmitter release in dorsal horn when given epidurally

Answer 35

opiates e.g. morphine

Question 36

which classes of analgesics reduces nociceptor sensitivity

Answer 36

opiates and NSAIDs