Lecture 1: History of Pain Flashcards
Learning outcomes: To define pain in history and modern times
The word pain is derived from where?
- Latin “poena” and Greek “poine” meaning “penalty” or “punishment”
Homer (7-9th BC) made what distinction between pain?
algos - central pain
odyne - peripheral pain (a painful wound)
Describe Plato, Hippocrates and Aristotle’s definitions of pain
Plato (4th BC): pain is a sensation and corresponds to the illness itself
Hippocrates (4th BC): pain happens to a body, suffering happens to a person (first to advice women giving birth to chew willow leaves - containing salicylic acid)
Aristotle (3rd BC): heart is the seat of feelings and pain was a feeling (his concept predominated for 2000yrs)
What was Galen’s (AD 129-199) role in the history of pain?
- the first physician thinking that pain was a sensation in which the brain & nerves played an important role
- recognised the importance of diagnostic value of pain
- classified forms of pain in terms we use today e.g. temperaments (physical condition of organs: hot or cold and dry or wet) & humours (blood, yellow bile, black bile & phlegm)
Perspective of pain in the middle ages?
- powerful spiritual and religious contexts (was also an important academic issue for physicians)
- analysis & alleviation of pain formed an important part of medicine developing within medieval universities
What were the common attitudes towards pain in western Europe during the middle ages?
- celebration or resigned acceptance of pain (F. Salmon)
: Leonardo da Vinci (1452-1519 AD) realised what regarding pain?
- dissecting and drawing he realized the fine relationship between the spinal cord, peripheral nerves and roots and connections to the brain
- “For Leonardo pain was a sensation mediated by nerves that also carry information about touch” (Perl)
A Vesalius (1514-1564) believed what about the brain and the nervous system?
- that the brain and the nervous system were the site of mind and emotions
What dramatic shift in conceptions in pain was seen in the late nineteenth century?
a ‘ gift from God’ to a physiological conundrum and medical challenge
Renee Descartes (1596- 1640) proposed what regarding pain?
the intensity of pain is directly related to the amount of associated tissue injury (specificity theory)
- Nerves are tubes inside which fine threads transmit sensory stimuli to the brain
CS Sherrington (1857-1952) in 1906 discovered what?
- (specialized nerve cell called) nociceptors whose molecular sensors are activated by harmful chemical or physical conditions
Tying pain only to the stimulus as proposed by R Descartes though does not account for the presence of pain in what situations? Give examples
- for pain without damage (e.g. phantom limb pain)
- or damage without pain (Beecher - WWII soldiers)
- or forms of chronic pain
what are the two main type of nerve fibres involved in the gate control theory of pain?
A-fibres: large diameter & fast-conducting nerve fibers (Aδ & Aβ)
C-fibres: smaller, slow-conducting fibers; they transmit pain signals i.e. open the gate & allow pain signals to reach the brain
What are the key nerve fibers involved in the gate control theory of pain?
A-delta (A-δ) and C-fibers
What is the function of A-delta (A-δ) fibers in the gate control theory?
Transmit sharp, fast pain signals & contribute to opening the pain gate
What is the role of C-fibers in the gate control theory?
- Transmit slow, dull, and aching pain signals.
- They are primarily responsible for keeping the pain gate open
where is the “gate” in the gate control theory of pain located?
- small interneurons in dorsal horn act as gate (which controls amount of excitation of transmission cells)
How does the gate control theory explain pain perception?
- suggests that pain perception depends on balance between A-δ and C-fiber signals, along with emotional and cognitive factors
- A-delta fibers tend to close the gate, while C-fibers tend to open it
What can influence the opening and closing of the pain gate in the gate control theory?
- Factors such as sensory information from A-delta fibers (closing) and C-fibers (opening), emotions, attention, and past experiences can modulate the gate
What role do Alpha-beta (A-β) fibers play in the gate control theory of pain?
- A-β fibers transmit non-painful sensations, such as touch & pressure
- they play crucial role in helping to close the pain gate in the theory
- when activated, they can inhibit the transmission of pain signals, reducing the perception of pain
What is the Gate Control Theory of Pain?
- proposed by Melzack and Wall (1965)
- asserts that non-painful input closes the nerve “gates” to painful input, which prevents pain sensation from traveling to the CNS
What is the gate control theory’s explanation for pain perception?
- Nociceptive stimuli activate primary afferent fibers, signalling transmission cells.
- ↑ transmission cell activity heightens pain perception, while ↓ activity lessens it
- A closed “gate” blocks input to transmission cells, reducing pain sensation, whereas an open “gate” permits input, allowing pain sensation
Who proposed the gate control theory, and what does it reconcile?
-Ronald Melzack and Patrick Wall in 1965.
- It reconciles the specificity and pattern theories of pain perception, providing a neural basis and revolutionizing pain research.
What is the focus of the study conducted by Duan et al. (2014) ?
- focuses on understanding the spinal cord’s role in processing mechanical pain signals
What are nociceptors and Aβ mechanoreceptors?
Nociceptors: Specialized receptors that detect harmful stimuli or pain.
Aβ Mechanoreceptors: Receptors that detect non-painful mechanical stimuli, like touch.
What is the role of inhibitory neurons (INs) in spinal pain processing?
- Inhibitory neurons are involved in gating Aβ inputs, controlling the activation of certain excitatory neurons, and regulating the perception of pain
Which specific excitatory neurons were found to be important for transmitting mechanical pain signals in Duan et al, (2014) study?
- Excitatory neurons expressing somatostatin (SOM) were identified as critical for transmitting mechanical pain signals
What happens when SOM+ excitatory neurons are ablated?
- Ablation of SOM+ excitatory neurons results in the loss of the ability to perceive mechanical pain
Which inhibitory neurons were found to be crucial for gating Aβ fiber inputs in the study?
- Inhibitory neurons expressing dynorphin (Dyn) were identified as crucial for gating Aβ fiber inputs
What is the role of the identified microcircuit in the Duan et al, (2014) study?
-the microcircuit (composed of peripheral mechanical nociceptors, Aβ mechanoreceptors, SOM+ excitatory neurons, and Dyn+ inhibitory neurons) is responsible for both transmitting & regulating mechanical pain signals in the spinal cord.
What did Gasser’s research highlight regarding pain control?
- Gasser’s work emphasized the importance of low-threshold mechanoreceptors in controlling pain by influencing peripheral neuron excitability
What did the study by Foster et al. (2015) establish regarding glycinergic dorsal horn neurons?
- that glycinergic dorsal horn neurons are key components of a spinal gate for pain and itch —> controlling the transmission of nociceptive signals in the spinal cord.
How does the International Association for the Study of Pain (IASP) define pain?
- an aversive sensory & emotional experience
typically caused by/resembling that caused by,
actual or potential tissue injury
What are the 3 components of pain?
- sensory-discriminative
sense of intensity location and duration - affective-motivational
unpleasantness and desire to escape it - cognitive component
involving judgments, beliefs, memories, perception of environment and patient’s own history
How has the treatment of pain changed over time?
- has evolved to include a multidisciplinary approach, combining medical treatment (including drugs & surgery), physical therapy, and psychological approaches like group CBT
What methods have replaced cutting nerves and pathways for pain management?
- Methods for modulating inputs, such as relaxation, hypnosis, acupuncture & the use of pain-management aids like TENS (Transcutaneous Electrical Nerve Stimulation) and heat packs, have replaced invasive procedures
