PAIN- Ballyk lecture Flashcards
what is algesia?
Sensitivity to pain
what is analgesia?
Absence of sensitivity to pain
What is hyper/hypoalgesia?
Increased or decreased sensitivity to pain
what is allodynia?
Pain sensation elicited by a normal non painful stimulus
What is dysesthesia?
Abnormal unpleasant sensation
What is nociceptive pain?
Normal pain functioning system
- Tissue damage
- Inflammatory pain
What is neuropathic pain?
Pain-reporting system is malfunctioning - perceive pain but no damage
- post-herpetic neuralgia
- central pain
- phantom limb pain
- diabetic neuropathy
What are the three types of nociceptors?
- Thermal (Adelta)
- Mechanical (A delta)
- Polymodal (C fibers)
Describe characteristics of thermal Nociceptors
- Respond to >45 and <5 degree temps
- Adelta fibers
- Fast pain (well-localized, not distressing)
- part of cutaneous nerve
Describe characteristics of Mechanical nociceptors
- Respond to intense pressure, nociceptive mechanical stimulus, pinch, pin prick
- HIGH threshold mechanoreceptors
- Adelta
Describe characteristics of polymodal nociceptors
- respond to mechanical, thermal or chemical stimuli
- DIFFUSE pain not well-localized, aching burning, SLOW Pain, distressing
- C fibers
What 2 things happen when a noxious stimulus is applied?
- Withdrawal reflex
2. Perception of pain - (post central gyrus)
2 mechanisms that inflammation results from
- Neurogenic inflammation (axon reflex)
2. Tissue damage
During the inflammatory event are pain signals sent to CNS?
YES, and nociceptors are sensitized
What are 3 things characterize inflammation?
- Redness
- swelling
- warmth
Neurogenic inflammation (axon reflex) characterized by
- C fiber transmit signals
- CGRP and Substance P are released from peripheral nerve
- change in blood vessels
- Mast cells release histamine
- platelets release 5-HT - serotonin
What are the effects on blood vessels after neurogenic inflammation?
- Vasodilate
- Increase permeability - plasma extravasation
- Release bradykinin -
What 3 things are released during an axon reflex that ACTIVATE nociceptors?
ALL ACTIVATE NOCICEPTORS
- Histamine
- Serotonin (platelets)
- Bradykinin (plasma)
What 3 things are released during an axon reflex FROM DAMAGED CELLS? SENSITIZE NOCICEPTORS
- K+ - sensitizes nociceptors
- Prostaglandins -
- Leukotrienes
What is released from the axon?
Substance P - also sensitizes
What does sensitization do?
Decreases activation threshold
Where does primary hyperalgesia occur?
In the skin region that is damaged
where does secondary hyperalgesia occur?
Adjacent region of the skin that was not damaged
What is mechanical hyperalgesia?
hyperalgesia to a mechanical stimulus that would not normally be painful
What is thermal hyperalgesia?
Hyperalgesia to a temperature that would not normally produce pain
What is the pain we feel due to?
sensitization of C fibbers by prostaglandins
3 effects of PGE2
- has no effect on its own
- enhances responses to Bradykinin
- produced from arachidonic acid by COX
Pain due to tissue damage is decreased by NSAIDs how?
- Analgesic effects
- Antipyretic effects
- anti-inflammatory effects
How do NSAIDs work?
Block COX, so block PGE2 synthesis
4 examples of NSAIDs
- ibuprofen
- indomethacin
- Naproxen
- Aspirin
What are the two ways in which inputs are integrated in the dorsal horn in nociception?
- Referred pain (convergent afferents from viscera)
2. Gate-control theory (inhibition from touch afferents)
How does referred pain work?
First order sensory neurone from 1) body wall 2) viscera (afferents) converge onto second order spinal neurons!
How does inhibition from touch afferents work?
1) First order neurone (C-fiber or Adelta pain fiber) ACTIVATES/OPENS the gate to STT
2) Abeta fiber activates inhibitory interneurons - collaterals, inhibit SECOND order neuron cLOSE the gate
What is the basis of the transcutaneous electrical stimulation for pain relief?
Inhibition from touch afferents
What is the function of the periaqueductal Grey Matter?
1) descending input to the dorsal horns
2) Release of enkephalins, endogenous opioids from dorsal horn interneurons
Enkephalins act on specific opioid receptors to inhibit pain 2 ways…
1) Inhibit NT release from the FIRST ORDER afferent nerve terminal
2) hyper polarize the post-synaptic SECOND order neurons
How do exogenous opioids act?
- Inhibit pain transmutation by binding.activating opioid receptors in first order and second order dendrite/cell body
What is responsible for the emotional response to nociception?
- SECOND order neurons in SL synapse onto
- THIRD order neurons in thalamus (RETIC?) project to
- Cingulate gyrus
NOT POST CENTRAL GYRUS
Does neuropathic pain activate nociceptors?
NO
When does neuropathic pain occur?
Damage to nerves/neural tissue in PNS, CNS (by injury or diseasE)
What 3 things may be involved with neuropathic pain?
- Allodynias
- Dysesthesias
- Hyper algesias
Give examples of neuropathic pain
- Peripheral damage
a) Diabetic neuropathy
b) Trigeminal neuralgia
c) Post-herpetic neuralgia - CNS damage
a) Post-stroke pain
b) brachial plexus avulsion pain
c) spinal injury pain
