Touch and pain part 2

Question 1

Congenital insensitivity to pain

Answer 1

Genetic condition in which you are born without nociceptors in body

Question 2

Consequence of congenital insensitivity to pain

Answer 2

No nociceptor means no feeling of pain : very problematic because pain is designed to protect us from injuries
- Prone to injuries, especially during childhood
- Most of the time, injuries affect body extremities

Question 3

Types of congenital insensitivity to pain

Answer 3

There is a cluster of patients in Quebec that have the second type of congenital insensitivity to pain, many who died young or have missing libs

Question 4

Usually genes that are associated with congenital insensitivity to pain will affect all____ ______ fibers, which are important for autonomic activity (heart rate, skin temperature, etc.)

Answer 4

small unmyelinated

Question 5

Limbic touch

Answer 5

Pleasant touch, kind of opposite of pain, emotional response

Question 6

Limbic touch is associated with…

Answer 6

Certain type of C-fibers (same for pain) sensitive to low intensity mechanical stimulation

Question 7

Patient with loss of tactile fibers in the body

Answer 7

• Cannot perceive anything with touch
• No largely myelinated fibers necessary to perceive touch
• Thermal sensation is preserved (difference threshold is kept) because small diameter fibers for temperature and pain are unaffected

Question 8

Limbic touch for patient with loss of tactile fibers

Answer 8

dissociation between the sensation and the emotion that is associated with it
- E.g stimulation perceived as lower, but says the sensation is as pleasant as control

Question 9

Limbic touch has these 2 types of receptors

Answer 9

1. Tactile receptors : sensation intensity encoding (brushing itself)
2. “Pleasantness” receptors : (small diamseter unmyelinated c-fibers) will encode the pleasantness of the brushing

Question 10

____ tactile fibers do not synapse in the dorsal horn in the spinal cord

Answer 10

Most

Question 11

Pathway of pain perception

Answer 11

1. The nociceptors enter the spinal cord and will make the first synapse in the dorsal horn of the spinal cord
2. The second neuron in the spinal cord, the spinal prediction neuron. will cross directly to the other side of the spine
3. The signal will ascend to the thalamus where there will be a second synapse
4. The signal will go from the thalamus to the cerebral cortex

Question 12

2 types of spinal projection neurons

Answer 12

1. Nociceptive specific :
   - Only responds to nociceptive information (stimulus in the noxious range)
2. Wide dynamic range
   - Most common kind of spinal projection neuron
   - Gradually increases its firing as a function of the intensity of the stimulus, and will respond even if the stimulation is in the non noxious range
   (Supports intensity theory)

Question 13

Pattern theories of pain

Answer 13

What matters is not necessarily the type of neuron that is activated, but the pattern of activity across a large position of neurons

Question 14

Ronald Melzak and Patrick Wall : Gate control theory

Answer 14

Explains why when you are in pain, gently stroking the injured body part slightly reduces pain

Question 15

neuron T in Gate control theory

Answer 15

Spinal transmission neuron in the dorsal horn of the spinal cord sending the information to an action system : the brain
- receives input from both C-fibers (nociceptive fibers) and A-fibers (tactile fibers)

Question 16

Central control in Gate control theory

Answer 16

the brain, which controls the gate system

Question 17

Inhibitory interneuron in the substantia gelatinos (dorsal horn of the spinal cord)

Answer 17

SG (-) neuron always inhibits the T neuron at baseline

Question 18

When only C fibers are activated (nociceptive) in Gate control theory

Answer 18

• The T neuron is activated
• At baseline, the SG (-) neuron always inhibit the T neuron, but because the SG neuron is inhibited (-) by activated C fibers, it won’t inhibit the T neuron;
• Therefore : more activation

Question 19

When only A-fibers are activated (touch) in Gate control theory

Answer 19

• The T transmission neuron is activated
• At baseline, the SG neuron always inhibit the T neuron without fibers activation, but because the inhibitory SG neuron is activated by A fibers, it increases the inhibition coming from the SG neuron even more
  Conclusion : the T transmission neuron is more activated by nociceptive C fibers than by tactile A fibers.

Question 20

When fibers C and A are active at the same time in Gate control theory

Answer 20

The pain is reduced because the total amount of activity is less than what you would get from just the activation of C fibers. Inhibitory interneuron is activated by A fibers counteracting the inhibition of the inhibition caused by C-fibers, reducing the activity of the T transmission neuron.

Question 21

When fibers C and A are active at the same time in Gate control theory, the T transmission neuron is ___less/more activated than when it’s just the C fibers.

Answer 21

Less ( NO reducing of inhibition that takes place when only the C fibers are activated)

Question 22

When fibers C and A are active at the same time in Gate control theory, the T transmission neuron is ___less/more activated than when it’s just the A fibers.

Answer 22

More

Question 23

Phenomenon being explained by gate control theory is associated with _______ neurons

Answer 23

wide dynamic range
- wide dynamic range neuron would respond just a little to non noxious tactile simulation
- It would respond a lot to noxious mechanical simulation.
- When the two are present (non noxious and noxious), it would have a medium response (less painful)

Question 24

Link between Pattern Theory and Gate Control Theory

Answer 24

What matters is not whether c-fibers are activated vs nothing, or a-fibers vs nothing, but rather the combination of activity across all fibers (if both a and c activated at the same time, pain is inhibited)

Question 25

Transcutaneous Electrical Nerve Stimulation (TENS)

Answer 25

- Administer a low intensity electrical current to the body part that hurts - Electrical current will be associated with a buzzing tactile sensation that masks the pain

Question 26

Chronic pain

Answer 26

Pain in absence of any body injury

Question 27

Opioids are powerful painkillers because they are good at ...

Answer 27

blocking transmission of nociception at the spinal cord level

Question 28

Action of opioids at the pre-synaptic neuron

Answer 28

- Activation of mu opioid receptors prevents calcium from entering into the synaptic terminal, which reduces the release of neurotransmitters into the synaptic cleft.

Question 29

Action of opioids at the postsynaptic neuron

Answer 29

Activation of mu opioid receptors results in the opening of potassium calcium channels resulting in the leaving of potassium out the neuron, which hyperpolarizes the membrane and makes it more difficult to depolarize.

Question 30

Placebo analgesia

Answer 30

May be associated with release of endogenous opioids

Question 31

Naloxone

Answer 31

- Works by blocking the mu opioid receptors - Preventing receptors from being activated by opioids - Reverses the placebo analgesia

Question 32

Pain tolerance is increased with an opioid placebo; what about with Naloxone ?

Answer 32

Naloxone by itself does not affect pain **Conclusion** : placebo analgesia is mediated by the release of endogenous opioids because naloxone blocking the opioids can reverse the process and abolish the placebo effect - Part of placebo is that is is as if you're really receiving the drug, but it's the nervous system that releases the opioids.

Question 33

Referred pain

Answer 33

- When a nociceptive signal is coming from a certain internal body organ but you do not feel pain in this organ - You rather feel the pain in another seemingly unrelated skin area

Question 34

What causes referred pain ?

Answer 34

1. Our nociceptive system is bad at detecting the location of pain when it happens in an internal organ (in the viscera) 2. Information from the internal organs will enter the spinal cord at different segments of it and sometimes will coincide with nociceptive information coming from a patch of skin

Question 35

In a heart attack, pain is felt to be spreading to the inside of the left arm. Why is that ?

Answer 35

Information from the heart enters the heart at the same level as information about that specific left arm dermatoma When you have a heart attack, you have an abnormally large nociceptive response : - massive release of neurotransmitter coming from the heart nociceptor in the dorsal horn of the spinal cord will cause a spillover effect where the spinal projection neuron, which is normally receiving information from the skin, will also get activated and will send that information to the brain : usually this activation means there is pain on the skin so this is what the brain will assume (on a less frequent occasion, it comes from the heart).

Question 36

Main difference between the tactile pathway (dorsal column pathway) and the pain pathway (spinothalamic tract)

Answer 36

- Pain information crosses over directly to the other side of the spinal cord then ascends to the thalamus and cortex - Touch information remains on the same side of the spinal cord and it only crosses over at the brainstem

Question 37

Brown-Séquard Syndrome

Answer 37

- Common in people with spinal cord lesions - dissociation between tactile deficits on one side and thermoalgesic deficits on the other side.

Question 38

Consequences of Brown-Séquard Syndrome

Answer 38

Results : - Loss of tactile sensation on same side as lesion (under lesion), however thermoalgesic (temperature and pain) sensation is preserved there - On the other side of the body : opposite dissociation, preserved tactile sensation, but loss in temperature and pain

Question 39

Pain modulation

Answer 39

- transmission of nociception in the spinal cord is not a one-way phenomenon - Information gets transmitted from the brain, but the brain can also modulate the transmission of nociception to the brain

Question 40

The ascending pathway

Answer 40

Spinothalamic pathway

Question 41

The descending pathway

Answer 41

- From brain to spinal horn of the spinal cord : brainstem plays an important rule in this (modulating nociception at the level of the spinal cord) - Helps cope with pain over time

Question 42

Conditioned pain modulation

Answer 42

- When pain inhibits pain - E.g. compare heat pain threshold on right hand before and after subjecting the left hand to painfully cold water - Result : increase in the pain threshold (person is less sensitive to pain after cold water immersion, not lukewarm)

Question 43

What causes conditioned pain modulation ?

Answer 43

As the pain ascends to the brain, it sends projections to the brainstem, triggering descending inhibitory controls - when those descending modulatory controls are activated, it's the whole body that is affected by them. - Allows you to cope with pain

Question 44

Fibromyalgia

Answer 44

- chronic pain disorder characterized primarily by widespread musculoskeletal pain, - accompanied by symptoms such as fatigue, cognitive disturbances ("fibro fog"), and sleep disruptions. - The condition involves increased sensitivity to pain, often described as widespread tenderness and heightened responsiveness of the nervous system.

Question 45

fibromyalgia is thought to result from abnormal pain processing within the central nervous system : ______descending/ascending inhibitory controls (inhibit pain throughout the body) have a deficit

Answer 45

Descending

Question 46

Condition A : asked to enter arm in a bath of painfully cold water from fingertips to shoulders Condition B : asked to remove full arm in cold water, fingertips at the end Which condition should produce the least pain in the fingertips? the increasing session or decreasing session ?

Answer 46

Condition B (decreasing) begins with more pain overall. This means that it is going to produce more pain inhibition. Therefore, there is less pain at the end of condition B (on the fingertips) than at the beginning of condition A (on the fingertips).

Question 47

Nociceptive flexion reflex (NFR)/the withdrawal reflex

Answer 47

- An involuntary spinal reflex triggered by potentially harmful (nociceptive) stimuli, such as heat or mechanical pressure. - It involves rapid contraction of flexor muscles to withdraw the affected limb from the source of pain, while simultaneously causing extension of muscles in the contralateral limb to maintain balance and stability (crossed-extension reflex).

Question 48

The NFR is widely used in pain research as an objective measure of ...

Answer 48

Spinal nociceptive processing and pain sensitivity (anything that influences the amplitude of this reflex can be interpreted as having an effect on the transmission of nociception at the level of the spinal cord)

Question 49

Study : Look at different kinds of pictures evoking emotions (pleasant, erotic, unpleasant, gore) , while receiving electric choc to the foot : measured the reflex with EMG What were the results of this ?

Answer 49

- increase in pain ratings for unpleasant pictures compared to neutral, reduction in pain for pleasant pictures compared to neutral. Amplitude of the nociceptive reflex showed a similar effect. - Effect was stronger when looking at unpleasant pictures

Question 50

Link between music and pain

Answer 50

Emotions induced by music create an analgesic effect, associated with spinal nociception