Pain Flashcards
What is the IASP definition of pain (2020)?
An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage
Why is pain response/experience different for every being?
Differs due to the context, their cognitive set, their mood and their brains chemicals and structure
(Also more basically - trauma, early life experiences and genetics)
What is nociception?
The neuronal process of encoding noxious stimuli (neural processing of pain). Nociceptive pain is pain caused by the activation of nociceptors.
Nocioception includes the reception, conduction and CNS processing of nerve of nerve signals that arise due to this activation.
What is a noxious stimulus?
Stimulus that’s damaging or threatens to damage normal tissues.
What is the difference between somatic and visceral pain?
Somatic : pain experienced from skin, muscle, bone damage/disease
Visceral : pain experienced because or organ pain (abdominal or thoracic)
What is wind-up?
Frequency-dependant increase in the excitability of spinal cord neurone, evoked by electrical stimulation of afferent C-fibres (spinal cord wound up by too many signals that then get confused for pain - common with chronic pain)
What is neuropathic pain?
Pain caused by a lesion or disease of the somatosensory nervous system - contrasts with nociceptive pain
Once pain signals travel onto the spinal cord what happens to them?
The either travel to the cortex in the brain or the limbic part of the brain
What is the cortex in the brain responsible for?
Picking up signals from sensitive parts of the body so it can identifying where the pain signals are coming from and the intensity of these signals
What is the limbic brain responsible for?
Emotions, response to threats, feelings, behaviour, mood ie. the affective aspects of pain
What effect do the ascending and descending pathways to the limbic system have on pain?
They can enhance or reduce pain by increasing or decreasing the pain signals travelling to the brain
This is unconscious and which is conscious out of pain and nociception?
Pain = conscious (perception of what’s happening in higher centres)
Nociception = unconscious (neural processing of stimuli)
What are nociceptors?
Pain receptors found as non-encapsulated nerve endings
What are the 3 possible pain stimuli?
- mechanical
- thermal
- chemical
What are the two pain fibre nociceptors?
A-delta fibres
C fibres
Where do the nociceptor fibres travel to once activated?
They travel up to the dorsal root ganglion and then into the grey matter of the spinal cord in organised layers, they then reach the brain
Which has myelinated fibres and which does not out of A and C?
How does this affect the fibre?
A is myelinated = fast conduction and well localised resulting in immediate sharp pain
C is unmyelinated = slow and not well localised resulting in a dull aching pain
Why is pain treatment often described as multimodal?
Lots of different chemicals involved in the pain response so multiple drugs my need to be used to target all of the chemicals
What are the two important ascending pathways in pain transmission?
- Spino(cervico)thalamic tract (major pain transmission pathway)
- Spinoreticular tract
What is the pathway of the spino(cervico)thalamic tract in humans and non-carnivores?
The first order neurone (primary afferent fibre) synapses at dorsal horn of the spinal cord, these synapse/connect with second order neurones (projection neurones) which cross over and ascend in the spinothalamic tract, the third order neurones arise in the contralateral thalamus and ascend to the cortex
(show by red pathway)
What does the spino(cervico)thalamic tract pick up on?
It is a primary pain pathway and picks up on touch and superficial pain
It is also highly discriminatory (has a high degree of somatotrpy- pin points pains location)
What is different in carnivores spino(cervico)thalamic tract?
They have 4 neutrons instead of 3 because they have 2 spinal projection neurones
(1 for the pelvic limb and 1 for the thoracic limb)
What is the pathway of the spinoreticular tract?
Primary afferent enters the spinal cord and diverges cranially and caudally spreading over several segments allowing intersegmental reflexes. The second-order afferents in the dorsal horn project to the reticular formation (the a few pass to the thalamus)
(blue pathway)
What information is passed to the brain by the spinoreticular tract and what does it activate?
Visceral sensations and deep pain that cannot be directly located/poorly localised due to the low ratio of A-delta fibres to C
Activates the limbic system which is what triggers an emotional response
Does pain in the head have to travel down and then back up via the spinal cord?
No, there are still 3 neurones but they enter the pins and course along the medulla
Why are there non-conscious responses to pain?
(like respiratory change or increase in epinephrine)
Ascending pathways connect to sub-cortical regions of the brain and the hypothalamus
Where are the 3 main places in which pain can be modulated?
- Peripheral modulation
2.Dorsal horn modulation (spinal cord)
3.Suprasegmental modulation (brain)
How does periphery modulation work?
How do anti-inflammatory drugs achieve this?
When chemicals released body tries to suppress the to reduce expression
Anti-inflammatory drugs achieve this by blocking receptors, stopping signal transmission
What are the conditions allodynia and hyperalgesia?
When intense pain is caused by very little stimulation
What is the purpose of the inhibitory interneurons that can be found between A-delta fibres and C fibres?
They can be stimulated to block the pain or they can be facilitated which lets the pain pass through - this is the ‘gate control’ theory of pain
How can A-delta fibres inhibit pain?
Stimulating A-delta fibres/large diameter fibres (this could be done by rubbing where you banged yourself) tells the inhibitory interneuron not to let the pain through.
A-delta are thick fibres = touch, vibration, pressure
C fibres are thin fibres = pain
What does a TENS-machine do?
Stimulates the A-delta fibres which inhibits the interneurons preventing pain transmission
Where does chronic pain usually originate from and what are the two cells involved in this called?
The dorsal horn
- Nociceptive specific neurones (NS)
- Wide dynamic range neurones (WDR)
Why is ketamine used for chronic pain?
Ketamine stops ‘wind up’
Ketamine works on the MNDA receptor by preventing activation, these are found in the WDR neurones in the dorsal horn which are involved in ‘wind up’.
What are the two nuclei in the brain that are responsible for suprasegmental modulation and what do they do?
Periaquaductal grey nuclei (PAG) - Responsible for the release of endorphins
Nucleus raphe magnus nuclei (NRM) - Responsible for the release of endorphins, serotonin, noradrenalin. Mood and well-being. Pain modulation.
Where do the descending pathways originate from?
Where suprasegmental modulation occurs
What are some paradoxical effects mediated through the ANS that pain can give rise to?
Neuroendocrine eg. impaired immune system
Cardiovascular eg. fatigue
Respiratory eg. decrease in lung volume
GIT & Urinary eg. decrease in bowel motility = constipation
MSK eg. immobility and fatigue
Psychological eg. fear
What is the fundamental must have of any pain scale?
Validity
(provides the evidence that the tool/questionnaire measures what it was designed to measure)
What are some examples of chronic pain questionnaires?
- Helsinki chronic pain index
- GuvQuest
- Liverpool osteoarthritis in dogs (LOAD e)
How is chronic pain multifactorial?
What is the main system involved in chronic pain?
Can show up in posture, mood, movement
Limbic system
In older animals, what syndrome can commonly be mistaken for pain?
Cognitive Dysfunction Syndrome
What should you do if you are in doubt about an animal is pain, or whether they are in pain, or how much pain they are in?
Give an analgesic and then after a few weeks re-asses
Is pain scoring used in large animals like cattle?
What are some of the issues with treating pain in cattle?
No, not often used
Few analgesics available, only 1 class so not often used clinically
