Lecture 1: History of Pain

Question 1

The word pain is derived from where?

Answer 1

• Latin “poena” and Greek “poine” meaning “penalty” or “punishment”

Question 2

Homer (7-9th BC) made what distinction between pain?

Answer 2

algos - central pain
odyne - peripheral pain (a painful wound)

Question 3

Describe Plato, Hippocrates and Aristotle’s definitions of pain

Answer 3

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)

Question 4

What was Galen’s (AD 129-199) role in the history of pain?

Answer 4

• 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)

Question 5

Perspective of pain in the middle ages?

Answer 5

• 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

Question 6

What were the common attitudes towards pain in western Europe during the middle ages?

Answer 6

• celebration or resigned acceptance of pain (F. Salmon)

Question 7

: Leonardo da Vinci (1452-1519 AD) realised what regarding pain?

Answer 7

• 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)

Question 8

A Vesalius (1514-1564) believed what about the brain and the nervous system?

Answer 8

• that the brain and the nervous system were the site of mind and emotions

Question 9

What dramatic shift in conceptions in pain was seen in the late nineteenth century?

Answer 9

a ‘ gift from God’ to a physiological conundrum and medical challenge

Question 9

Renee Descartes (1596- 1640) proposed what regarding pain?

Answer 9

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

Question 10

CS Sherrington (1857-1952) in 1906 discovered what?

Answer 10

• (specialized nerve cell called) nociceptors whose molecular sensors are activated by harmful chemical or physical conditions

Question 11

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

Answer 11

• for pain without damage (e.g. phantom limb pain)
• or damage without pain (Beecher - WWII soldiers)
• or forms of chronic pain

Question 12

what are the two main type of nerve fibres involved in the gate control theory of pain?

Answer 12

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

Question 13

What are the key nerve fibers involved in the gate control theory of pain?

Answer 13

A-delta (A-δ) and C-fibers

Question 14

What is the function of A-delta (A-δ) fibers in the gate control theory?

Answer 14

Transmit sharp, fast pain signals & contribute to opening the pain gate

Question 15

What is the role of C-fibers in the gate control theory?

Answer 15

• Transmit slow, dull, and aching pain signals.
• They are primarily responsible for keeping the pain gate open

Question 16

where is the “gate” in the gate control theory of pain located?

Answer 16

• small interneurons in dorsal horn act as gate (which controls amount of excitation of transmission cells)

Question 17

How does the gate control theory explain pain perception?

Answer 17

• 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

Question 18

What can influence the opening and closing of the pain gate in the gate control theory?

Answer 18

• Factors such as sensory information from A-delta fibers (closing) and C-fibers (opening), emotions, attention, and past experiences can modulate the gate

Question 19

What role do Alpha-beta (A-β) fibers play in the gate control theory of pain?

Answer 19

• 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

Question 20

What is the Gate Control Theory of Pain?

Answer 20

• 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

Question 21

What is the gate control theory’s explanation for pain perception?

Answer 21

• 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

Question 22

Who proposed the gate control theory, and what does it reconcile?

Answer 22

-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.

Question 23

What is the focus of the study conducted by Duan et al. (2014) ?

Answer 23

• focuses on understanding the spinal cord’s role in processing mechanical pain signals

Question 24

What are nociceptors and Aβ mechanoreceptors?

Answer 24

Nociceptors: Specialized receptors that detect harmful stimuli or pain. Aβ Mechanoreceptors: Receptors that detect non-painful mechanical stimuli, like touch.

Question 25

What is the role of inhibitory neurons (INs) in spinal pain processing?

Answer 25

- Inhibitory neurons are involved in gating Aβ inputs, controlling the activation of certain excitatory neurons, and regulating the perception of pain

Question 26

Which specific excitatory neurons were found to be important for transmitting mechanical pain signals in Duan et al, (2014) study?

Answer 26

- Excitatory neurons expressing somatostatin (SOM) were identified as critical for transmitting mechanical pain signals

Question 27

What happens when SOM+ excitatory neurons are ablated?

Answer 27

- Ablation of SOM+ excitatory neurons results in the loss of the ability to perceive mechanical pain

Question 28

Which inhibitory neurons were found to be crucial for gating Aβ fiber inputs in the study?

Answer 28

- Inhibitory neurons expressing dynorphin (Dyn) were identified as crucial for gating Aβ fiber inputs

Question 29

What is the role of the identified microcircuit in the Duan et al, (2014) study?

Answer 29

-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.

Question 30

What did Gasser's research highlight regarding pain control?

Answer 30

- Gasser's work emphasized the importance of low-threshold mechanoreceptors in controlling pain by influencing peripheral neuron excitability

Question 31

What did the study by Foster et al. (2015) establish regarding glycinergic dorsal horn neurons?

Answer 31

- 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.

Question 32

How does the International Association for the Study of Pain (IASP) define pain?

Answer 32

- an aversive sensory & emotional experience typically caused by/resembling that caused by, actual or potential tissue injury

Question 33

What are the 3 components of pain?

Answer 33

- 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

Question 34

How has the treatment of pain changed over time?

Answer 34

- has evolved to include a multidisciplinary approach, combining medical treatment (including drugs & surgery), physical therapy, and psychological approaches like group CBT

Question 35

What methods have replaced cutting nerves and pathways for pain management?

Answer 35

- 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