Sensory Systems (Including Physiology of Pain) Flashcards Preview

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Flashcards in Sensory Systems (Including Physiology of Pain) Deck (34):
1

sensory receptors respond to stimulus over a specific area, what is the area called?

receptive field

2

what do sensory receptors transduce their adequate stimulus into?

a depolarisation, the receptor (generator) potential

3

what encodes the intensity of the stimulus

size of receptor potential
then frequency of action potentials

4

what does the receptor potential evoke?

firing of action potentials for long distance transmission

5

what encodes the location of the stimulus?

receptive field

6

what is proportional to duration of a series of action potentials?

stimulus duration

7

what determines acuity?

Density of innervation, and size of receptive fields

8

what are 3 types of primary afferent fibres that mediate cutaneous sensation?



C

9

describe Aβ fibres

large myelinated (30-70m/s) touch, pressure, vibration

10

describe Aδ fibres

small myelinated (5-30m/s) cold, “fast” pain, pressure

11

describe C fibres

unmyelinated fibres (0.5-2m/s) warmth, “slow” pain

12

what are 2 types of primary afferent fibres that mediate proprioception & mechanoreception?

Aα & Aβ

13

what are 2 types of primary afferent fibres that mediate thermoreception & nociception ?

Aδ & C

14

describe the pathway of mechanoreceptive fibres

project straight up through ipsilateral dorsal columns
synapse in cuneate & gracile nuclei
the 2nd order fibres cross over midline in the brain stem

15

describe the pathway of thermoreceptive & nociceptive fibres

synapse in the dorsal horn
the 2nd order fibres cross over the midline in the spinal cord
project up through the contralateral spinothalamic (anterolateral) tract

16

where do the Primary afferent fibres project in the brain?

reticular formation, thalamus and cortex

17

what is affected when there is damage to dorsal columns?

causes loss of touch, vibration, proprioception below lesion on ipsilateral side

18

what is affected when there is damage to anterolateral quadrant?

causes loss of nociceptive & temperature sensation below lesion on contralateral side

19

where is the ultimate termination of sensory information?

sensory homunculus
in the somatosensory cortex (S1) of the postcentral gyrus

20

what is neural/sensory adaption?

change over time in the responsiveness of the sensory system to a constant stimulus
ie action potentials stop firing after putting on clothes

21

what is the difference between fast and slow adaptation?

Fast adaptation occurs immediately after stimulus presentation i.e., within 100s of milliseconds.
Slow adaptive processes that take minutes-days

22

what is neural convergence?

One postsynaptic cell receives convergent input from a number of different presynaptic cells (saves on neurones but reduces acuity, may underlie referred pain)

23

describe lateral inhibition

activation of one sensory fibre causes synaptic inhibition of its neighbours
gives better definition of boundaries
cleans up sensory information

24

what is chronic and phantom limb pain due to?

neural plasticity

25

what are nociceptors activated by?

low pH, heat (via ASIC, TRPV1 etc)
local chemical mediators (eg bradykinin etc)

26

what are the two ways the body inhibits pain?

Segmental controls
Descending controls

27

what activates the inhibitory interneurones in segmental controls?

activity in Aα/β fibres

28

describe how Inhibitory interneurones inhibit pain

release opioid peptides (endorphins) that inhibit transmitter release from Aδ/C fibres, hence “closing the gate”

29

what activates the Inhibitory interneurones in decending controls?

descending pathways from brain:
Peri-aqueductal grey matter (PAG) Nucleus raphe magnus (NRM)

30

how do Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit pain?

prostaglandins sensitise nociceptors to bradykinin

NSAIDS block prostaglandins so bradykinin signal stays small

31

how are NSAIDS anti-inflammatory?

they inhibit cyclo-oxygenase which converts arachidonic acid to prostaglandins

32

how do Local anaesthetics inhibit pain?

block Na+ action potential and therefore all axonal transmission
(why area affected is numb)

33

how do Trans cutaneous electric nerve stimulation (TENS) inhibit pain?

increases activity in Aα/β fibres (segmental control activated)

34

how do Opiates (eg morphine)
inhibit pain?

reduce sensitivity of nociceptors
block transmitter release in dorsal horn (hence epidural administration)
activate descending inhibitory pathways