Physiology Of Pain 1 Flashcards
Classifications of Pain
Nociceptive
Inflammatory
Neuropathic
What is pain
Unpleasant sensory experience associated with tissue damage
via A delta and C fibres
What is a nociceptor
First order neuron of spinothalamic tract
Pseudo unipolar (central and peripheral axon)
primary sensory
What do A alpha and beta fibres fibres detect?
-comment on diameter and myelin content
Detect light touch and proprioception
Myelinated
Large diameter
Which fibres detect sharp pricking pain?
-comment on this fibre’s diameter and myelin content
A Delta fibres Detect light touch, temperature and noiception, sharp 'pricking' pain thinly myelinated medium diameter low in viscera
Which fibres detect slow, dull aches and burning pains?
-comment on this fibre’s myelin content and diameter
C fibres Detects temperature, noiception Unmyelinated Small diameter Slow burning pains, itch, dull ache
What channel is activated by high temperature?
TRPV1
CHILLI is an agonist of which channel
TRPV1
Where does the spinothalamic tract synapse in the dorsal horn
Substantial gelatinosa
How does stress induced analgesia occur?
PAG neurons excite RVM, which inhibits the spinothalamic tract
Opioids
Found in both CNS and PNS
Inhibitory- so act on inhibitory metabotropic receptors
How does ATP directly activate nociceptors?
Binds to purinergic receptors (p2X)
How does H+ directly activate nociceptors?
Binds to acid sensing ion channels
What is referred pain?
convergence of visceral and cutaneous nociceptor on same second order neurons in spinal cord
Why is pain felt in upper left arm after an MI?
convergence on 2nd order neuron from visceral nociceptor from heart and cutaneous nociceptor from skin over left arm
How does stress induced analgesia occur?
PAG (Periaqueductal gray matter) excite RVM (Rostral Ventromedial medulla) neuones, which inhibit (or excite) the spinothalamic tract
What is allodynia?
Non-noxious stimuli produce a painful responce
What is hyperalgesia?
Noxious stimuli produce an exaggerated pain response
What is peripheral sensitization
Increase in responsiveness of peripheral ends of nociceptors
driven by tissue injury or inflammation
Bradykinin and NGF reduce the threshold of heat activated (TRPV1)
Prostaglandins reduces threshold of sodium channels
Describe the mechanism of action of Bradykinin
Binds to receptor (metabotropic-GPCR)
Activation of protein kinase phosphorylates TRPV1 (this phosphorylation reduces threshold of channel so it fires more easily)
