pain overall Flashcards
(24 cards)
Definition of pain
The subjective conscious appreciation of a stimulus that is causing, or threatening to cause, tissue damage. Pain exists in your cerebral cortex!!
Nociception definition
The physical process of detection and transmission of damaging or potentially damaging (noxious) stimuli
Nociceptors definition
Structures/Receptors which detect noxious stimuli – peripheral tissues
Algesia definition
The induction of a condition leading to nociception and pain
Analgesia definition
Reduction or prevention of either nociception or pain without loss of consciousness
types of pain
- Acute - short term - Local inflammatory changes, intensity affected by inflammatory mediators
- chronic - progressive - Peripheral and central sensitizations
3 different levels of pain procession
- Nociception
- Peripheral activation and release of pain mediators - Pain gating
- Dorsal horn of the spinal cord - Pain perception
- The brain (thalamus, limbic and cortical systems)
What are the two routes for pain signal transmission?
ascending pathway: pathway that goes upward carrying sensory information from the body via the spinal cord towards the brain
- Conveys pain stimuli from
spinal cord to higher brain
centres
descending pathways: neural pathways that goes downward from the brain to the reflex organs via the spinal cord
- Neurons that can affect or
alter neuronal signals in
ascending pathway
How Nociceptors are stimulated
High mechanical stimulation, thermal stimulation, Low pH
Chemicals (often from inflammatory response)
Released by tissue damage
- Bradykinin,
- histamine (itch)
Sensitivity of these channels affected by
- Bradykinin (up)
- Prostaglandins (up)
- Opioids (down)
What are the two types of pain?
fast/first pain - small myelinated adelta fibres
- usually transient, a sensation
of sharp, well localised pain
- triggers reflex to move away
from source of pain
slow/second pain - non-myelinat6ed C fibres
- less easily localised low conduction velocities cause a dull burning pain
Ascending pain pathways - spinothalamic tract
Sensory input from first order afferent neuron enters spinal cord via dorsal horn
Synapses with second order neuron (crosses)
Travels through medulla to thalamus
Synapses with third order neuron in thalamus
Third order neuron extends to primary somatosensory cortex
What is allodynia?
Pain to a non-noxious stimulus (When you feel pain even if there is no stimulus, so you feel pain when you usually wouldnt at all)
What is hypergalgesia
Increased pain to a mildly noxious stimulus, can be peripheral or central. (When you feel greater pain after a stimulus then usual. You feel pain when usually it would only be a tingle, usually during an injury)
What happens during peripheral sensitisation?
Increased sensitivity of nociceptors
What happens during central sensitisation?
Increased transmission in spinal cord
- increased stimulation in the primary afferent fibre leads to an even larger action potential in the second neurone.
Repeated stimulation increases the amplitude of the synaptic potential
Caused by NMDA glutamate receptors
Neurokinin receptors (C fibres)
Can be prevented by
Reducing peripheral stimulation
can can we inhibit that central stimulation?
Gate theory
- some second order neurones can be excited by c fibres and non-pain sensory fibres (A-alpha or A-beta e.g mechano-receptors)
- also connected via a inhibitory neuron - excited by sensory nerve fibre and can suppress nociceptive/pain signals
What analgesics to use for peripheral pain?
Non-opioid
Aspirin
Paracetamol (acetaminophen),
NSAID : ibuprofen, naproxen, diclofenac –
(All anti-pyretic – only NSAID and aspirin anti-inflammatory)
NSAID and aspirin
Inhibit COX/COX2 (Catalyses generation of PGE2 from arachidonic acid)
Paracetamol less clear
What group of signalling molecules do NSAIDs prevent being generated?
Postaglandins
What are the 3 main types of opiod receptors?
mu, kappa and delta
How do opiods inhibit nociception (peripheral)?
Opioids open K channels
K-efflux
hyperpolarisation
or
Opioids close Ca-channels
reduced Ca-signalling
reduced excitability
How do opiods inhibit the ascending pain pathway?
Inhibit excitation in periphery
- Inhibits ascending pathway
Inhibit transmission in Dorsal horn
- Inhibits ascending pathway
Activate descending pathway
- Inhibits ascending pathway
List the main opiod drugs
opiates:
- morphine
- codeine
synthetic:
- heroin
- oxycodone
- methadone
- pethidine
- pentazocine
- fentanyl
- buprenorphine
antagonist:
- naloxone/naltrexone
Whats the most common receptor targeted for opiods?
Mu
What are the opiod effects at different receptors?
Respiratory centre (medulla)
- Respiratory depression
- can occur at therapeutic dose
GI tract
- reduced mortility
- constipation
cough centre of medulla
- depression of cough reflex
chemoreceptortrigger zone (medulla)
- nausea, vomiting
- usually transient
pupillary constriction
- occulomotor nucleus - pinpoint pupils
- diagnostic in induced coma
