The pain experience 1: Peripheral mechanisms

Question 1

what is the role of the nociceptive system?

Answer 1

to signal threat or the occurrence of injury

Question 2

what is the anatomy of nociceptors?

Answer 2

Free nerve ending attached to either Aδ or C fibres

Question 3

are Aδ fibre nociceptors myelinated?

Answer 3

yes

Question 4

what kind of pain do Aδ fibre nociceptors give?

Answer 4

Fast, sharp pain that’s easily localised

Question 5

what are the 2 types of Aδ fibre nociceptors

Answer 5

Aδ mechanical nociceptors
Aδ polymodal nociceptors

Question 6

what do Aδ mechanical nociceptors respond to?

Answer 6

strong mechanical stimuli

Question 7

what do Aδ polymodal nociceptors respond to?

Answer 7

all types of noxious (damaging) stimuli

Question 8

are C-fibre nociceptors myelinated?

Answer 8

no

Question 9

what kind of pain do C-fibre nociceptors give?

Answer 9

Slow, burning pain that’s poorly localised and longer lasting

Question 10

what is the one type of C-fibre nociceptors?

Answer 10

polymodal C-fibre nociceptors

Question 11

what do polymodal C-fibre nociceptors respond to?

Answer 11

all types of noxious (damaging) stimuli

Question 12

what is graded potential?

Answer 12

local change in membrane potential. this is caused by a small stimulus causing depolarisation but not meeting the threshold potential

Question 13

how does a mechanical stimulus cause an action potential?

Answer 13

mechanically sensitive ion channels

Question 14

how does thermal a stimulus cause an action potential?

Answer 14

Lots of channel types that respond to different temperatures e.g. TPRV1 channels open if >43c, TRPM8 channels open if <28c

Question 15

how does a chemical stimulus cause an action potential?

Answer 15

local tissue damage produces algogenic (pain formation) substances. These can activate or sensitise (smaller stimulus has bigger response) nociceptive nerve endings

Question 16

name 7 algogenic substances

Answer 16

ATP
H+
K+
histamine
serotonin
bradykinin
prostaglandins

Question 17

what causes the algogenic substance ATP to be released?

Answer 17

mechanical cell damage

Question 18

how does the algogenic substance ATP cause depolarisation?

Answer 18

activates Na channels P2X3

Question 19

what causes the algogenic substance H+ to be released?

Answer 19

Low pH conditions e.g. lactic acid produced during exercise

Question 20

how does the algogenic substance H+ cause depolarisation?

Answer 20

Activates TRPV1 receptor and acid sensing ion channel (ASIC) that are Na+ permeable

Question 21

what causes the algogenic substance K+ to be released?

Answer 21

mechanical cell damage

Question 22

what is histamine released by?

Answer 22

mast cells

Question 23

does histamine sensitise or activate nociceptive nerve endings ?

Answer 23

sensitise in low conc.
activate in high conc.

Question 24

what is serotonin released by?

Answer 24

mast cells and platelet aggregation

Question 25

does serotonin sensitise or activate nociceptive nerve endings?

Answer 25

sensitise in low conc.
activate in high conc.

Question 26

what is bradykinin?

Answer 26

Potent algogenic substance that sensitises or activates

Question 27

what are prostoglandins?

Answer 27

Lipid released by tissue damage cause pain and inflammation

Question 28

do prostaglandins sensitise or activate nociceptive nerve endings?

Answer 28

sensitise

Question 29

where is substance P released from?

Answer 29

nerve endings as a result of the axon reflex

Question 30

what does substance P do?

Answer 30

vasodilation, increase in vascular permeability, mast cell degranulation

Enhances activity of TRP1 and P2X3 nociceptors

Question 31

what is hyperalgesia?

Answer 31

exaggerated response to a noxious/nociceptive stimulus

Question 32

what is allodynia?

Answer 32

pain produced by a stimulus that would not normally cause pain e.g. sunburn, tender tooth

Question 33

what are analgesics?

Answer 33

medications that relieve pain e.g. Aspirin

Question 34

how do analgesics work?

Answer 34

Cox inhibtors which stops the production of prostaglandins reducing pain and inflammation

Question 35

where is the site of receptors for touch in the mouth?

Answer 35

PDL

Question 36

where is the site of receptors for pain in the mouth?

Answer 36

dentine/pulp
PDL

Question 37

where is the site of receptors for cold in the mouth?

Answer 37

gingiva
dentine/pulp

Question 38

what are the afferent nerves in the pulp?

Answer 38

Aδ myelinated afferents
C-fibre unmyelinated afferents
Aβ myelinated afferents

Question 39

name this zone of the pulp

Answer 39

pulp core

Question 40

name this zone of the pulp

Answer 40

cell rich zone

Question 41

name this zone of the pulp

Answer 41

cell free zone of Weil

Question 42

name this zone of the pulp

Answer 42

odontoblast layer

Question 43

name this zone of the pulp

Answer 43

plexus of Raschkow

Question 44

what causes pulpal pain?

Answer 44

substance P
C-fibres

Question 45

what are the 3 theories of dentine sensitivity?

Answer 45

dentine is innervated
odontoblast receptor theory
hydronamic theory

Question 46

what is the odontoblast receptor theory?

Answer 46

Communication between odontoblasts and primary afferents

Question 47

what is the hydronamic theory?

Answer 47

Fluid flow in dentinal tubules results in action potentials in pulpo-dentinal nerves

Question 48

how does fluid flow cause dentinal pain in the hydronamic theory?

Answer 48

Stretch sensitive ion channels in nerve endings

ATP released from odontoblasts (P2X3 channels)