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Flashcards in Perception of Pain Deck (46):
1

What does perception of pain depend on?

Situation
Emotion
Genetic susceptibility
Previous experience

2

Which parts of nociceptive nerves detect painful stimuli?

Free unspecialised nerve endings with 'pain channels' inserted in the membrane

3

What is the most common pain channel?

Transient Receptor Potential family of channels (TRP)

4

What are pain channels sensitive to?

O2
pH
Osmolarity
Valinoids (capsicum)
Heat

5

Name 6 substances that can sensitise pain channels

Substance P
Bradykinins
Serotonin
pH
ATP
NO

6

What s the structure of a pain channel?

6-unit transmembrane protein with a basket of regulatory complexes in the cytoplasm

7

What effect do extreme temperatures have on Transient Receptor Potential Vanilloid (TRPV) channels?

Allow entry of sodium and calcium causing depolarisation leading to AP

8

How do CGRP and substance P increase sensitivity to pain?

Recruit silent receptors which increase summation in the dorsal horn

9

How does histamine cause sensitisation?

Acts on blood vessels

10

What is the role of bradykinin in pain?

Acts on pain receptors directly and causes an increase in prostaglandins

11

Why does weight lifting cause muscle ache?

Tissue damage produced H+ which causes muscle ache

12

How do NSAIDS such as aspirin prevent pain?

Inhibit COX enzyme which is involved in the production of prostaglandin E2

13

Describe A-delta fibres

Myelinated
Sharp 1st pain
Detect extreme temperatures

14

Describe C fibres

Unmyelinated
Secondary slow pain
Burning or aching pain
Thermal and chemical stimuli

15

Which neurotransmitters do nociceptive fibres release?

Glutamate
Substance P
CGRP

16

What effect does peripheral neurotransmitter release have?

Red flare
Tenderness

17

What are the 3 physiological signs of pain and what is their physiological cause?

Calor (heat) - local hyperaemia
Rubor (redness) - local hyperaemia
Tumour (swelling) - plasma extravasation

18

Which system is the ascending pain system?

Anterolateral

19

Where does descending pain regulation occur?

Periaqueductal gray

20

What information is carried in the paleospinothalamic pathway?

Slow burning

21

What information is carried in the neo-spinothalamic pathway?

Fast sharp pain

22

Where does the neo-spinothalamic pathway terminate?

VPL of thalamus

23

Where does the paleo-spinothalamic pathway terminate?

DM and intralaminar nuclei of thalamus

24

Where does the discriminating pathway project?

Primary somatosensory cortex

25

Where does the undiscriminating pathway project?

Limbic system association cortices

26

What is the role of the spinoreticular pathway?

Motor response and ascending arousal

27

Describe the mechanism of wind up

When WDR fire at high frequency, they open NMDA channels
Calcium influx increases number of Na channels and blocks K channels
Resting potential closer to threshold
==> more sensitive cell (amplifies pain signal)

28

What is the purpose of wind up?

Priority salience
Protection from further injury
Memory

29

Which directly causes the variation in cell sensitivity by WDR neurones?

Intensity of C fibre stimuli

30

Describe pain modulation at the dorsal horn

Strong activation
- C fibres stimulate WDR neurones and inhibit the inhibitory interneuron

Weak activation (i.e. when you rub a bump)
- AB fibres activate inhibitory interneuron and WDR neurons
-Inhibitory interneuron inhibits WDR neurons which prevents sensitisation

31

Name an endogenous substance that can provide descending analgesia

Enkephalin

32

Why is the basis behind the high efficacy of opioids?

Can act simultaneously at all levels of the pain pathway via the endogenous opioid system

33

Name 3 classes of endogenous opioids

Endorphins
Encephalins
Dynorphins

34

Name 2 areas of the limbic system involved in pain

Cingulate gyrus - activated when we see others in pain
Insula - emotional, motivational and modulatory

35

Give examples of persistent neuropathic pain

Causalgia
Phantom limb pain
Carpel Tunnel Syndrome
Peripheral neuropathy

36

What is allodynia?

Painful reaction to non-noxious stimuli like light touch

37

What is summation?

Repeated low innocuous stimuli causing increasing intensity of response

38

What are dysesthesias?

Burning or shooting pain without stimulation which can sometimes be associated with thalamic syndrome

39

What causes central maladaption?

Increase in NMDA receptors
Descending modulation of inhibitory interneurons leading to reduced inhibition of WDR

40

What is central maladaption?

Long term changes in the structure of synapses in the dorsal horn of spinal cord leading to sensitisation

41

What is the proposed cause of headache?

Irritation of venous sinuses, meninges and capillaries

42

Why do you get a headache after excessive alcohol consumption?

Alcohol irritates meninges
Dehydration

43

Why does low CSF cause headache?

Brain settles onto the base of the skull causing deformation of dura

44

Describe the mechanism of referred pain

Pain signals and cutaneous signals enter spinal cord at same point
Cross talk in dorsal horn can cause signals from viscera to get picked up by ascending neurons that are mapped to the dermis

45

Which NT does the PAG release to modulate pain in the dorsal horn?

NA

46

Which NT does the PVN and raphe nucleus release?

5-HT