Week 5 Pain + Temperature + Itch Flashcards

Question

Gate Theory of Pain

Answer 1

-Processing within the spinal cord - Within the spinal cord there are mechano and nociceptive fibres but also populations of interneurons that facilitate or inhibit incoming information -Gate cells and transmission cells within spinal cord When non-nociceptive touch info arrives in the spinal cord, this activates the gate cell, which inhibits the T cell -Lock on gate firm =gate opening inhibited - When pain info arrives in the spinal cord, this inhibits the gate cell, which disinhibits the T cell, allowing the T cells to actively transmit pain -Releases lock on gate=gate opening allowed=pain sensation

Answer 2

- Transmission (T) cells -Transmit pain info onwards, up toward the brain - Gate cells -Work to ‘gate’ the activity of the T cells, tonically inhibit the T cells

Answer 3

- If you can influence the gate you can influence pain perception - uses top down modification + bottom up modifications and exogenous control

Answer 4

o Increase cutaneous sensation to try and shut the gate o From the periphery o Turn on gate cell to stop transmission of pain – provide very stong mechanoreceptive input o Give yourself mechano stimuli -Touch the area that hurts right away -Rub and injury – shuts the gate within spinal cord -Trying to activate gate cell to reduce T cell pathways

Answer 5

o Send a message from the brain to shut the gate o Signal from the brain o Strong central signal telling gate cell to activate and inhibit T cell  Subconsciously – brain initiates top down modification right away  Consciously – central control component, send excitatory signal to gate cell  Activating pathway – people can block the pain, learned to control descending pathways and activate it themselves  Endurance sports – combat signals telling you to stop running  Placebo to treat pain – if you think this will help, maybe activate descending pathways and reduce ascending pain pathway o Might be enough to actually reduce pain perception o Pathway is descending from SI  Descending pathways modulate transmission of ascending pain signals  E-stim of descending path inhibits activity of 2nd order nociceptive neurons (T-cells) and produces analgesia – reduction of pain o Descending path contains enkphalin, endorphin and dynorphins  Endogenous opioids  Relief from pain o Start to train people about the descending pathway to reduce pain  If we can use non-prescription drugs it will be a good thing  Effect is the same – activate descending pathway endogenously as opposed to exogenously using opioids

Answer 6

o Use an exogenous drug to help shut the gate o Descending pathway responds to opiate drugs – exogenous opioids  Activate the same pathway – help shut gate in spinal cord

Answer 7

o Since birth, an inability to feel pain (insensitivity) or lack of responsiveness to pain (indifference) o Sometimes accompanies by Thermoreception deficits o Genetic mechanisms increasingly understood  NaV1.7 mutations  NaV1.9 variants  Difference in sodium channels mean that nociceptors don’t work in the normal way o Peripheral neuropathy  Something going wrong in the peripheral, before the spinal cord

Answer 8

o Nociceptive stimuli are felt in a sensory component but without the affective component there is less/no unpleasantness/suffering  Can feel pain but neutral to it - indifference o Common aetiology  CNS pathology – something noticeably wrong in brain + spinal cord  Surgical brain resectioning  Remove part of cingulate or internal capsule – central components causing pain perception  Opioids, to a degree, also achieve a level of asymbolia  Can become physically dependent – relief from psychological pain  Work at descending pathway – activate receptors in brain to reduce responsiveness to pain in an affective state  Less suffering, don’t really care – helps heal better - Sensory limbic dissociation o Si and SII both go to motor cortex but SII also goes to limbic system – give emotional affective component of touch as well o In pain it is bad, negative emotion associated o If this becomes disconnected then you lose this limbic reaction to sensory information - Pain matrix o Need cingulate, insula, prefrontal and limbic (as well as SI and SII) o They give cognitive components to respond and formulate a plan – also give the qualia ‘this hurts’ o If there is disconnect it removes some of the sense of pain or significance of it

Answer 9

- Alerts you to tissue damage o A warning signal that tissue damage has occurred or is about to occur  Don’t continue with the situation – have hurt your body somehow and need to deal with it o Very difficult to ignore that signal o Initiates an immediate behavioural response -Prompts behavioural change to ensure survival o In you: hyperalgesia  Repetitive application of stimuli results in sensitisation  A warning signal to stop doing this o In you: allodynia  Normal touch stimuli becomes painful  Leads to protection of injured area – allows healing o In others: physical help, attention, empathy  Responses in other – come to help  To help your survival

Answer 10

- We all have different pain thresholds – we all experience pain differently and we all handle pain differently - Partly due to physiology -Partly due to physcholgy

Answer 11

``` o Degree of FNE innervation  More = more sensitive o Number and types of TRP receptors, NaV1 receptors, etc.  Encoded by genes o Skin properties  Have to get through layers of dermis ```

Answer 12

o Selected attention  Attend to the painful sensations and fixate – makes it worse  Makes you have a lower threshold to subsequent stimuli  Don’t pay attention to it – alleviate threshold  If there is something that is more pressing  You don’t pay attention to the pain until afterwards when you are safe, then pain kicks in  Reduce pain perception with distraction  Provide distracting stimuli – draws attention away from pain o Socialreferencing  Inbuilt idea of conforming to social norms  From the moment something painful happens to us as infants – a baby looks to those around them to see how to react  Male – suppress crying from pain more than a female  Societal norms – how we should respond based on age, gender o Emotional state  Mood – nervous, happy, sad  Affects how you perceive pain, how you handle it  Anxious – stimulus is more painful  Fear – expectation of pain will enhance the perception  Look away from the needle or look towards is to know where the pain is coming from  Knowing it and mitigating it helps not feeling the pain as much  For others it will exacerbate the pain due to the fear  Negative affect – bad mood – things are more painful o Noxious stimuli applied following induction of a sad mood are more painful o Pain thresholds generally lower following exposure to negative slide scenes  Mood effect the emotional aspect of pain perception o When in pain you usually feel sad – makes it worse o Personality traits  Lifelong personality differences  Do you carry trait anxiety, neuroticism?  When you do experience pain do you suck it up, go home and cry, make a huge drama  Suppress it or play it up – subconsciously or consciously  Pain elicits behavioural responses in other people – we know this and use this  Catastrophizing chronic pain  Intensification of emotional and cognitive components of pain perception (overwhelmed, judging tasks unachievable)  May elicit social support but is counterproductive ... increases distress and fosters disability  Intensifies affective component o Sensory experience may not change but alters cognitive component  Usually is underlying pain – makes it very well known to other to a greater degree  Munchausen syndrome  Psychiatric syndrome of feigning illness/disease to gain attention  Munchausen-by-proxy transfer to use of children to fulfil psychological need for attention  Nothing is wrong and you know this o Make it up to get behavioural reaction from other o Do the research to feign the right symptoms to get attention in clinical setting

Answer 13

- No obvious bottom-up mechanism – nothing in periphery that should be causing pain - Treating pain is one of the biggest challenges in modern medicine o Nociceptive pain o Neuropathic pain  Can't see what is going on  In peripheral nerves in spinal cord  If something is wrong in the pathway – abnormal activity firing, causes pain o Psychosomatic pain  Nothing cutaneously wrong, or peripherally or centrally  Something psychologically manifesting as physical pain  Treating this is a particularly tough challenge  Historically viewed with scepticism  Finally seeing a shift in medicine: pain can be top-down  If you activate pain matrices in the brain, pain qualia will result  Need to treat this

Answer 14

- Itching = an unpleasant sensation that evokes the desire to scratch - Acute pruritus is useful – tells you something is on the skin - Chronic pruritus can be miserable o Pruriceptive  Something wrong cutaneously  Something causing the itch – bite, rash o Neuropathic  Abnormally firing in the pathway that carries itch o Psychogenic  Something wrong psychologically, manifesting physically as itch o Systemic  Things that go wrong in the body that manifest as itchiness  Renal failure, thyroid, bile  Side effect of itch - Itch appears to stem from activation of specific A delta and C fibres that express certain receptors/combinations of receptors o H1 histamine receptors – activated by histamine o TRPV1 + H1 histamine – activated by capsaicin and histamine o MrgA3 receptors – activated by chloroquine o 5-HT2 serotonin receptors – activated by 5-HT

Answer 15

- Pruritogens (stimuli) activate specific types of receptors on FNEs (A delta and C fibres) - This results in signal transduction - Unique neural relay? o Uses spinothalamic – a shared pathway with nociception and Thermoreception - Unique cortical processing o Pruritogenic stimuli cause activation in  SI  Need to know where you're itching and how much  Is it itch vs mechanoreception or pain  Motor areas  Pre-supplementary motor area, SMA itself, M1 o Makes sense when you think about the response we have  We scratch – definitive loop  The minute we feel itch we scratch and move away  Itch-scratch cycle - Itch is perceptually intriguing o The qualia seems to be easily elicited by the idea of itch o Just the mention of it, verbally, visually – can cause qualia o Is this a blurring of perception and conception? Is it inception – causing it in someone