Somatosensation and Pain

Question 1

What does the limbic system play a key role in?

Answer 1

regulating emotions, memory and behaviour

Question 2

What does the limbic system include?

Answer 2

• amygdala
• hippocampus
• hypothalamus

Question 3

What is the role of the amygdala?

Answer 3

• processes emotions like fear, anger and pleasure
• helps recognise emotional cues
• triggers fight or flight response

Question 4

What is the role of the hippocampus?

Answer 4

declarative memory i.e. crucial for forming and retrieving memories linked to emotions to contextualise emotional experiences based on past events

Question 5

What is the role of the hypothalamus?

Answer 5

regulates emotional responses by controlling autonomic functions like heart rate, blood pressure, and hormone release, which are linked to emotional states

Question 6

How does pain serve as a critical protective mechanism?

Answer 6

it alerts the body to potential or actual harm

Question 7

What are the 3 main components of pain?

Answer 7

1. sensory-discriminative aspect
2. affective-motivational aspect
3. cognitive-evaluative aspect

Question 8

What does the sensory-discriminative aspect of pain involve?

Answer 8

the physical sensation of pain, including its intensity, location, quality and duration

Question 9

What is the mechanism of the sensory-discriminative aspect of pain?

Answer 9

pain signals are initiated by nociceptors and are transmitted through peripheral nerves to the spinal cord and then to the brain, where they are processed primarily in the somatosensory cortex, allowing the individual to localise and describe the pain

Question 10

What does the affective-motivational aspect of pain refer to?

Answer 10

the unpleasant emotional and psychological responses associated with pain, such as fear, anxiety, and the urge to escape the painful stimulus regulated by the limbic system

Question 11

What does the cognitive-evaluative aspect of pain involve?

Answer 11

the interpretation and meaning assigned to the pain experience, including beliefs, attitudes, and expectations about pain, as well as coping strategies

Question 12

What is nociceptive pain?

Answer 12

pain that results from actual or potential tissue damage, typically protective in nature, often described as sharp, aching, or throbbing

Question 13

Give an example of nociceptive pain

Answer 13

pain from a cut, burn, or broken bone

Question 14

What is neuropathic pain?

Answer 14

(often chronic) pain caused by damage to or dysfunction of the nervous system itself, described as burning, shooting, or electric shock-like

Question 15

Give an example of neuropathic pain

Answer 15

pain from diabetic neuropathy, shingles or nerve compression

Question 16

What is inflammatory pain?

Answer 16

pain associated with inflammation, which occurs when the body’s immune response triggers the release of chemicals that sensitise nociceptors

Question 17

Give an example of inflammatory pain

Answer 17

pain from rheumatoid arthritis

Question 18

What is chronic pain?

Answer 18

pain that persists for longer than 3-6 months, often resulting from ongoing tissue damage, nervous system dysfunction, or sensitisation

Question 19

Give an example of chronic pain

Answer 19

chronic back pain, fibromyalgia, migraine headaches

Question 20

What is pain intensity?

Answer 20

the sensory dimension of the pain experience, which often translates into the quantity of the pain experienced

Question 21

What is pain unpleasantness?

Answer 21

the emotional dimension of the pain experienced, or the extent to which the pain is considered uncomfortable or bothering

Question 22

What happened to neural activity in the ACC when pain unpleasantness was decreased via hypnosis?

Answer 22

it also decreased

Question 23

What happens when pain signals reach the ACC?

Answer 23

they trigger emotional and behavioural responses aimed at avoiding or escaping the painful stimulus

Question 24

What does activity in the ACC correlate to?

Answer 24

the subjective feeling of how unpleasant the pain is, rather than just the intensity of the pain stimulus

Question 25

What is allodynia?

Answer 25

pain to a normally non-painful stimulus

Question 26

What are possible mechanisms of touch allodynia?

Answer 26

• peripheral sensitisation
• central sensitisation
• disinhibition
• aberrant sprouting
• altered brain processing
• involvement of glial cells

Question 27

When does peripheral sensitisation occur?

Answer 27

when PNS nociceptors become more sensitive and responsive to stimuli

Question 28

What is the mechanism of peripheral sensitisation?

Answer 28

after tissue injury or inflammation, nociceptors can lower their threshold for activation, meaning that even light touch can activate them and send pain signals to the brain (inflammatory mediators can also contribute to this)

Question 29

What is the result of peripheral sensitisation?

Answer 29

increased sensitivity of primary afferent neurons (especially Aδ and C-fibres)

Question 30

What is central sensitisation?

Answer 30

increased responsiveness of CNS neurons, particularly in the dorsal horn of the spinal cord, to normal or subthreshold sensory input

Question 31

What are the 3 mechanisms of central sensitisation?

Answer 31

• increased synaptic efficiency (repeated stimulation of nociceptors → increased neurotransmitter release and activation of NMDARs in dorsal horn neurons → LTP)
• loss of inhibitory control (inhibitory interneurons become less effective through loss of GABA or glycinergic inhibition)
• spinal cord rewiring (Aβ fibres synapse on neurons that normally transmit pain signals)

Question 32

What is disinhibition?

Answer 32

a reduction in the inhibitory control that normally prevents non-painful stimuli from being perceived as painful

Question 33

What is the mechanism of disinhibition?

Answer 33

destruction of inhibitory interneurons, such as those in lamina II of the dorsal horn, leads to a loss of inhibition on pain-processing neurons

Question 34

Give an example of disinhibition

Answer 34

the loss of dynorphin-expressing neurons, which inhibit pain pathways, can result in increased excitability of pain-transmitting neurons → touch allodynia

Question 35

What is aberrant sprouting?

Answer 35

abnormal growth of CNS nerve fibres e.g. after injury, Aβ fibres may sprout and form new synaptic connections with neurons in the dorsal horn that usually receive input from nociceptive fibres

Question 36

How can altered brain processing cause touch allodynia?

Answer 36

brain regions e.g. somatosensory cortex and ACC may become hyperactive or reorganised which amplifies the perception of touch leading to the sensation of pain even in response to light touch

Question 37

How can glial cells cause touch allodynia?

Answer 37

after injury or inflammation, glial cells can become activated and release pro-inflammatory cytokines and chemokines that enhance the excitability of pain-processing neurons and enhance the central sensitisation

Question 38

What is LTP?

Answer 38

a form of synaptic plasticity that makes these neurons more responsive to incoming signals

Question 39

What are the 6 steps of long-term modulation of spine plasticity?

Answer 39

1. nociceptive afferent, on intense activation by peripheral damage, releases relative excessive glutamate at glutamatergic synapse on 2nd order neurons
2. glutamate combines with NMDARs, which facilitates the rise in calcium in the 2nd order neurons
3. calcium phosphorylates AMPARs which increase the excitability of the receptor
4. elevated calcium also triggers translocation of AMPARs to the membrane, which increases the excitability of the 2nd order neurons
5. postsynaptic messengers travelling from the synapse to the nucleus of the 2nd order neuron trigger calcium signalling in the nucleus and activation of CREB-dependent genomic programmes
6. this about long-term modulation of spine structure and density

Question 40

Give examples of touch allodynia

Answer 40

• sprained ankle
• sunburn
• neuropathy