The pain experience 1: Peripheral mechanisms Flashcards
what is the role of the nociceptive system?
to signal threat or the occurrence of injury
what is the anatomy of nociceptors?
Free nerve ending attached to either Aδ or C fibres
are Aδ fibre nociceptors myelinated?
yes
what kind of pain do Aδ fibre nociceptors give?
Fast, sharp pain that’s easily localised
what are the 2 types of Aδ fibre nociceptors
Aδ mechanical nociceptors
Aδ polymodal nociceptors
what do Aδ mechanical nociceptors respond to?
strong mechanical stimuli
what do Aδ polymodal nociceptors respond to?
all types of noxious (damaging) stimuli
are C-fibre nociceptors myelinated?
no
what kind of pain do C-fibre nociceptors give?
Slow, burning pain that’s poorly localised and longer lasting
what is the one type of C-fibre nociceptors?
polymodal C-fibre nociceptors
what do polymodal C-fibre nociceptors respond to?
all types of noxious (damaging) stimuli
what is graded potential?
local change in membrane potential. this is caused by a small stimulus causing depolarisation but not meeting the threshold potential
how does a mechanical stimulus cause an action potential?
mechanically sensitive ion channels
how does thermal a stimulus cause an action potential?
Lots of channel types that respond to different temperatures e.g. TPRV1 channels open if >43c, TRPM8 channels open if <28c
how does a chemical stimulus cause an action potential?
local tissue damage produces algogenic (pain formation) substances. These can activate or sensitise (smaller stimulus has bigger response) nociceptive nerve endings
name 7 algogenic substances
ATP
H+
K+
histamine
serotonin
bradykinin
prostaglandins
what causes the algogenic substance ATP to be released?
mechanical cell damage
how does the algogenic substance ATP cause depolarisation?
activates Na channels P2X3
what causes the algogenic substance H+ to be released?
Low pH conditions e.g. lactic acid produced during exercise
how does the algogenic substance H+ cause depolarisation?
Activates TRPV1 receptor and acid sensing ion channel (ASIC) that are Na+ permeable
what causes the algogenic substance K+ to be released?
mechanical cell damage
what is histamine released by?
mast cells
does histamine sensitise or activate nociceptive nerve endings ?
sensitise in low conc.
activate in high conc.
what is serotonin released by?
mast cells and platelet aggregation
does serotonin sensitise or activate nociceptive nerve endings?
sensitise in low conc.
activate in high conc.
what is bradykinin?
Potent algogenic substance that sensitises or activates
what are prostoglandins?
Lipid released by tissue damage cause pain and inflammation
do prostaglandins sensitise or activate nociceptive nerve endings?
sensitise
where is substance P released from?
nerve endings as a result of the axon reflex
what does substance P do?
vasodilation, increase in vascular permeability, mast cell degranulation
Enhances activity of TRP1 and P2X3 nociceptors
what is hyperalgesia?
exaggerated response to a noxious/nociceptive stimulus
what is allodynia?
pain produced by a stimulus that would not normally cause pain e.g. sunburn, tender tooth
what are analgesics?
medications that relieve pain e.g. Aspirin
how do analgesics work?
Cox inhibtors which stops the production of prostaglandins reducing pain and inflammation
where is the site of receptors for touch in the mouth?
PDL
where is the site of receptors for pain in the mouth?
dentine/pulp
PDL
where is the site of receptors for cold in the mouth?
gingiva
dentine/pulp
what are the afferent nerves in the pulp?
Aδ myelinated afferents
C-fibre unmyelinated afferents
Aβ myelinated afferents
name this zone of the pulp
pulp core
name this zone of the pulp
cell rich zone
name this zone of the pulp
cell free zone of Weil
name this zone of the pulp
odontoblast layer
name this zone of the pulp
plexus of Raschkow
what causes pulpal pain?
substance P
C-fibres
what are the 3 theories of dentine sensitivity?
dentine is innervated
odontoblast receptor theory
hydronamic theory
what is the odontoblast receptor theory?
Communication between odontoblasts and primary afferents
what is the hydronamic theory?
Fluid flow in dentinal tubules results in action potentials in pulpo-dentinal nerves
how does fluid flow cause dentinal pain in the hydronamic theory?
Stretch sensitive ion channels in nerve endings
ATP released from odontoblasts (P2X3 channels)
