Lecture 25 - Pleasure and Pain I Flashcards Preview

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Flashcards in Lecture 25 - Pleasure and Pain I Deck (35):
1

Aspects of the pain experience
1)
2)
3)

1) Pain is always subjective
2) It is an experience
3) Relationship between pain and tissue damage is variable

2

Way that touch and joint sense are projected to the brain
1)
2)

1) Receptors in skin project to dorsal column nuclei.
2) Dorsal column nuclei project to the thalamus via the Medial lemniscus

3

Way that nociceptive signals project to the brain
1)
2)

1) Receptors in the skin project to neurons in the dorsal horn
2) Receptors in the dorsal horn project to thalamus, via the spinothalamic tract

4

Example of nociceptors that project to the dorsal column

GIT nociceptors

5

Cutaneous mechanoreceptors
1)
2)
3)
4)
5)

1) Hair follicles
2) Meissner corpuscle
3) Pacinian corpuscle
4) Merkel cell-neurite complex
5) Ruffini corpuscle

6

Skin stimulus detected by Meissner corpuscle

Dynamic deformation. Objects slipping over skin.

7

Skin stimulus detected by Pacinian corpuscle

Vibration

8

Skin stimulus detected by Merkel cell-neurite complex

Indentation depth. For fine tactile discrimination.

9

Skin stimulus detected by Ruffini corpuscle

Stretch.

10

Two types of C-fibre mechanoreceptors

1) LTM, responsible for pleasant contact.
2) Polymodal nociceptor (with Adelta fibres)

11

Example of a transducer in polymodal nociceptors

TRPV1

12

TRPV1

A cation channel (Ca2+, Na+) in Adelta and C-fibres (nociceptors)

13

Four functional types of nociceptors

1) Thermal (Adelta fibre)
2) Mechanical (Adelta fibre)
3) Polymodal (C-fibre)
4) Silent (C-fibre)

14

Things that polymodal C-type fibres can detect
1)
2)
3)
4)

1) Noxious heat
2) Noxious cold
3) Peptidergic receptors (noxious peptides)
4) Nonpeptidergic

15

Ion channel types in nociceptive neurons
1)
2)
3)
4)
5)

1) Transient Receptor Potential channels (EG: TRPV1)
2) Voltage-gated Na+ channels
3) Hyperpolarisation-activated cation channels
4) K+ channels
5) Voltage-gated Ca2+ channels

16

Functional difference between Adelta and C fibres

Adelta are larger, myelinated, faster conducting.
C-fibres are smaller, unmyelinated, slower conducting

17

Silent nociceptors

C-fibres.
Not active in normal tissues. Activated when a tissue is damaged.

18

Nociceptors in hairy skin

Adelta, C

19

Nociceptors in glabrous skin

Only C-fibres

20

Pain that Adelta are responsible for

Sharp pain

21

Pain that C-fibres are responsible for

Slow, burning pain

22

Differential projection of Adelta and C-fibres into the spinothalamic tract
1)
2)

1) C-fibres project to superficial layers (layers I and II)
2) Adelta project to deeper layers (IV, V)

23

Proportion of neurons in the dorsal horn that project to the brain

5-10%

24

Evidence that nociceptor activation doesn't have to result in emotional response to pain

Reflex pathways of the dorsal horn

25

What can lead to referred pain?

Two nociceptive inputs converging on the one spinal circuit

26

Primary hyperalgesia

Tissue is damaged, leading to release of factors (EG: prostaglandin, bradykinin from mast cells).
This leads to nociceptors being easier to depolarise.

27

Allodynia

Sensation of pain from light touch

28

Difference between primary and secondary hyperalgesia

Primary occurs in the tissues that were damaged.
Secondary occurs in undamaged tissues surrounding damaged tissues

29

Area responsible for sensory aspect of pain

Projections to primary somatosensory cortex

30

What correlates with phantom limb pain?

Functional remodelling in brain of somatosensory cortex (detected with fMRI)

31

Non-somatosensory parts of brain that are activated in nociception

Prefrontal cortex, anterior cortex, singulate cortex.

32

Example of pain not correlating with tissue damage

Hot/cold grill results in sensation of burning heat

33

Affective-motivational pain pathway

1) Anterolateral system
2) Middle thalamic nuclei
3) Insular cortex and anterior singulate gyrus

34

Sensory-discriminative pain pathway
1)
2)
3)

1) Anterolateral system
2) Ventral posterior nucleus
3) Somatosensory cortex (S1, S2)

35

Outcome of the complex network of centres stimulated by nociception in the brain.

Experience of pain is modulated by emotional factors
Positive emotion reduces unpleasantness of pain
Lack of attention to pain reduces intensity of pain