Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOM30001 - Frontiers in Biomedicine > Lecture 26 - Pain & Pleasure I > Flashcards

Lecture 26 - Pain & Pleasure I Flashcards

1
Q

State the IASP definition of Pain

A

“Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

List some features of the pain experience

How is pain experienced?

How can this experience be affected?

How is pain expressed?

A
  • Always subjective (no objective measure)
  • Extent of the tissue damage can be a poor indicator of the pain being experienced
    • The relationship between tissue damage and pain is variable
  • Pain is only experienced when nociceptive signals form the tissue reach the conscious brain
    • Pany cognitive factors can thus affect the pain experience
      • Culture
      • Beliefs
      • Past experience
      • The situation
  • Pain is expressed in behaviour
    • This is how one expresses pain to others
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the ‘pain pathway’

Describe endogenous inhibition of this pathway

Summarise exogneous inhibition of various points along this pathway

A
  1. Free nociceptor nerve endings in the tissue
    • TRPV1
      • Capsaicin
    • TRPV3
      • Mustard
  2. Action potential transmission along axon
    • Voltage gated Na+ channels
  3. Cell body in dorsal root ganglion
  4. Synapse on neuron in dorsal horn of spinal cord
    • Glutamate onto NMDA & AMPA receptors
  5. 2° neuron ascends several spinal segments
  6. Decussation
  7. Ascends up lateral spinothalamic tract
  8. Synapse on thalamus
  9. Third order projections to:
    • Post central gyrus
    • Peri-aquaductal grey (PAD)

Descending pain control pathway:

  • Projections from PAD release inhibitory neurotransmitters onto first synapse in the Rexed lamina
    • Noradrenaline (NA)
    • Serotonin (5-HT)
  • These projections are stimulated by endogenous opioids
  • “Walking wounded”

Gate theory of analgesia

  • Mechanoreceptors inhibit the first synapse in the spinal cord by releasing inhibitory neurotransmitters
    • GABA
    • Glycine

Exogenous inhibition:

  • Exogenous opioids activate the PAD
  • TCA (tricyclic antidepressants), such as Amitryptyline inhibit uptake of NA and 5-HT at first synapse
  • Deep brain stimulation activates the PAD
  • NSAIDs inhibit the generation of prostaglandins
  • Local anaesthetic inhibits voltage gated Na channels, thus inhibiting neural transmission of nociceptors
  • Ketamine inhibits NMDA receptors in first synapse
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe how cognition can affect perception of pain

A

Pain is processed by certain areas in the brain:

  • Amygdala etc.

that contribute psychological components to the experience of pain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe pain as a sensory experience

A

Once nociceptor signals reach the thalamus, there are thrid order projections to the post-central gyrus (ie somatosensory cortex)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe the sensory pathway of visceral pain

A
  1. Nociceptor free nerve endings in organs
  2. Cell body in dorsal root ganglion
  3. First synapse in spinal cord
  4. Ascends up a few segments
  5. Decussation
  6. Ascends in dorsal columns
    • Like somatosensory neurons
    • As opposed to nocicpetors from skin which ascend in lateral spinothalamic tracts
  7. Synapse on thalamus
  8. Thrid order projections to Insular cortex
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

List the various aspects of sensation in the skin

A
  1. Hair follicles

– Aβ fibres –

  1. Meissner corpuscle
    • Dynamic deformation (slipping)
  2. Pacinian corpuscle
    • Vibration
  3. Merkel cell
    • Indepntation depth
  4. Ruffini corpuscle
    • Stretch

– **C-fibres **–

  • Free nerve endings, no specialised terminals
  1. Touch
    • Pleasant touch
    • Low threshold
    • Sensory + pleasure
  2. Nociception
    • When intensity of stimulus is noxious

– Aδ fibres –

  1. Nociception
    • Sensory + affective
    • Noxious pain / itch
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

List tissues in which nociceptors are found

A
  • Skin
  • Joints
    • Within the joint, the nociceptors has simple nerve terminals, like in the skin
    • Mechanosensors in the joint have more specialised terminals, as in the skin
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Compare sensory transmission to noxious and mechanical stimuli

A

Mechanical stimulus:

  • eg touching an object
  • Aα fibres fire at a constant rate while the object it being touch
  • Stop firing once the stimulus is removed

Noxious stimulus

  • eg flame on finger
  • Aδ fibre fires at an increasing rate while the stimulus is present
  • Firing continues once the stimulus is removed, tissue damage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe detection of pain by eating chillies

A
  • Chili contains capsaicin
  • Capsaicin activates TRPV1 channels on the free nerve endings of nociceptors (Aδ fibres)
  • Aδ fibre fires
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Outline the functional nociceptor classes

A
  1. Thermal
    • Aδ fibres
    • TRPV1 channel (and others)
      • Sensitive to heat
    • TRPM8 channel (and others)
      • Sensitive to cold
      • Activated by Menthol
  2. Mechanical
    • Aδ fibres
  3. Polymodal
    • C fibres
  4. Slient
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Outline the various channels present on nociceptors

A
  1. Peripheral terminal
    • TRPs
      • Transient receptor potential channels
      • Sensitive to pressure, heat, cold, molecules etc.
      • Na+ and Cl- channels once activated: initiate action potentials
  2. Peripheral axon
    • **Nav: **voltage gated sodium channels
    • **Kv: **voltage gated potassium channels
    • **HCN: **hyperpolarisation activated cation channels
  3. Central axon and synapses
    • **Cav2.2: **voltage gated calcium channel
    • Cav3.2
    • Control the exocytosis of synaptic vesicles containing neurotransmitters, thus controlling the synapse
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Which type of fibres are nociceptors?

Give features of each

Describe nerve propagation in each

A

Aδ fibres

  • Lightly myelinated
  • Pain, temperature
  • Sharp, acute pain
  • *

C fibres

  • Unmyelinated
  • Pain, temperature, itch
  • Slow, burning pain
  • *
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the name for non-hairy skin?

A

Glaborous skin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where do second order pain neurons ascend in the spinal cord?

A

In the spinothalamic tract

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe spinal reflexes

What has this got to do with pain?

A

Nociception without pain

  1. Stimulus: stretch on tibialis
  2. Activation of nociceptive fibres
  3. Synapse on interneurons
  4. Activation of motor neurons for tibialis
  5. Contraction of tibialis
17
Q

Describe referred pain

A
  1. Activation of nociceptors in viscus
  2. Neural transmission to spinal cord and up to brain
  3. Thalamus
  4. Projections to post-central gyrus
  5. Perception of pain in the skin supplied by the same nerve root
18
Q

What is hyperalgesia?

Outline the mechanism

A

Decreased pain threshold following injurous stimulus

Mechanism:

  • Peripheral sensitisation
    1. Tissue damage
    2. Release of prostaglandins, bradykinin etc.
      • Diffuse into surrounding, undamaged tissue aswell
    3. These molecules bind to GPCRs
    4. Phosphorylation of TRPs
    5. Decreased threshold of TRPs in peripheral terminals in damaged tissues and surrounding, non-damaged tissue
  • Central sensitisation
    • Upregulation of NMDA and AMPA
    • Nociceptors in far reaching non-damaged tissue now sensitised (lower threshold)
19
Q

Differentiate between primary and secondary allodynia and hyperalgesia

What brings about each?

A

Primary allodynia/hyperalgesia

  • Brought about by peripheral sensitisation
    • ie increased TRP channel sensitivity
  • Lower intensity noxious stimuli will elicit pain

Secondary allodynia/hyperalgesia

  • Brought about by central sensitisation
  • Innocuous stimuli will elicit pain
20
Q

When does secondary hyperalgesia occur?

A

Sustained exposure to noxious stimulus

21
Q

Where is the somatosensory cortex?

A

Post-central gyrus

22
Q

Describe pain in phantom limbs

What has fMRI told us about this?

A

Pain experienced in a limb that has been amputated

fMRI:

  • Areas of the brain that map the amputated limb are active whilst the pain is being experienced in the phantom limb
  • Areas that map the ‘phantom limb’ are re-mapped and expanded in response to the loss of sensory input from the limb
23
Q

Outline how attention and mood affect experience of pain

A
  1. Attention
    • Intensity predominantly attenuated when distracted from pain
    • Unpleasantness reduced to a lesser degree
  2. Mood
    • Predominantly affects the affective component of pain
    • Unpleasantness diminished when in good mood
    • Also intensity, to a more marginal extent
24
Q

Which molecules can activate TRPV1 channels?

What happens after activation?

A
  • Capsaicin

Molecules released by damaged tissues:

  • H+
  • Lipids

After activation:

  • Conformational change in the receptor
  • Na+ and Ca2+ ions move through the channel into the cell
25
Q

What determines the functional class of the nociceptor?

A

The channels present on the neuron

  • eg TRPV1 present on heat encoding nociceptors
26
Q

Compare the speed of propagation of pain and somatosensation signals to the brain

A

Propagation from end of toe to brain:

Pain:

  • 1-2 seconds
  • Lightly myelinated axons of A-delta fibres

Somatosensation

  • 1-2 milliseconds
  • Heavily myelinated somatosensor neurons
27
Q

Describe the anatomical distribution of the first synapse of nociceptive signals

A

The first synapse occurs in the dorsal horn of the spinal cord

  1. C fibres
    • Project to superficial laminae (I and II)
  2. Aδ fibres
    • Project to deeper laminae, as well as superficial laminae (to a certain extent)
28
Q

List areas of the brain that are involved in pain perception, besides the 1° and 2° somatosensory cortex

What is the general role of these areas in pain?

A
  • Prefrontal cortex
    • Higher brain function
    • Non-sensory functions, eg cognition, emotion
  • Insula
  • Posterior parital cortex
  • Anterior cingulate gyrus

Role:

  • Contribute to the ‘affective’ components of the pain experience (as opposed to the sensory components)
29
Q

Describe the thermal grill illusion of pain

A

Thermal grill:

  • Alternating warm and cool bars

Results:

  • When bars are experienced individually, they are not noxious
  • When hand is placed on the grill, the individual experiences burning pain (noxious heat)

Brain imaging:

  • Area of anterior cingulate gyrus active during noxious heat stimulus also active when hand on grill.
  • This area is not active when experiencing cool or warm stimuli

Explanation:

  • Cool stimulus:
    • Upon cool stimulus, both ‘cool’ and ‘noxious cold’ sensors are activated
    • ‘Cool’ receptors inhibit ‘noxious cold’ nociceptors
    • Insula inhibition of anterior cingulate
    • Experience of only coolness (not cold pain)
  • Thermal grill
    • Activation of variety of sensors:
      • Cool
      • Noxious cold
      • Warm
    • ‘Warm’ and ‘cool’ sensors negate each other
    • Noxious cold sensors activate anterior cingulate
    • Experience of cold pain
30
Q

What is responsible for the ‘affective’ component of pain?

What does this account for?

A

Nociceptor projections to non-somatosensory areas of the brain:

  • Insular cortex
  • Anterior cingulate cortex

Furthermore, there is interaction of these areas with others:

  • Reticular formation
  • Hypothalamus
  • Amygdala

This accounts for experience of pain being dependent on factors such as mood and attention.

BIOM30001 - Frontiers in Biomedicine (35 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions