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Neurophysiology > Perception of Pain > Flashcards

Perception of Pain Flashcards

1
Q

What does perception of pain depend on?

A

Situation
Emotion
Genetic susceptibility
Previous experience

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2
Q

Which parts of nociceptive nerves detect painful stimuli?

A

Free unspecialised nerve endings with ‘pain channels’ inserted in the membrane

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3
Q

What is the most common pain channel?

A

Transient Receptor Potential family of channels (TRP)

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4
Q

What are pain channels sensitive to?

A 
O2
pH
Osmolarity 
Valinoids (capsicum)
Heat
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5
Q

Name 6 substances that can sensitise pain channels

A 
Substance P
Bradykinins 
Serotonin 
pH
ATP
NO
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6
Q

What s the structure of a pain channel?

A

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

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7
Q

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

A

Allow entry of sodium and calcium causing depolarisation leading to AP

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8
Q

How do CGRP and substance P increase sensitivity to pain?

A

Recruit silent receptors which increase summation in the dorsal horn

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9
Q

How does histamine cause sensitisation?

A

Acts on blood vessels

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10
Q

What is the role of bradykinin in pain?

A

Acts on pain receptors directly and causes an increase in prostaglandins

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11
Q

Why does weight lifting cause muscle ache?

A

Tissue damage produced H+ which causes muscle ache

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12
Q

How do NSAIDS such as aspirin prevent pain?

A

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

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13
Q

Describe A-delta fibres

A

Myelinated
Sharp 1st pain
Detect extreme temperatures

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14
Q

Describe C fibres

A

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

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15
Q

Which neurotransmitters do nociceptive fibres release?

A

Glutamate
Substance P
CGRP

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16
Q

What effect does peripheral neurotransmitter release have?

A

Red flare

Tenderness

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17
Q

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

A

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

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18
Q

Which system is the ascending pain system?

A

Anterolateral

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19
Q

Where does descending pain regulation occur?

A

Periaqueductal gray

20
Q

What information is carried in the paleospinothalamic pathway?

A

Slow burning

21
Q

What information is carried in the neo-spinothalamic pathway?

A

Fast sharp pain

22
Q

Where does the neo-spinothalamic pathway terminate?

A

VPL of thalamus

23
Q

Where does the paleo-spinothalamic pathway terminate?

A

DM and intralaminar nuclei of thalamus

24
Q

Where does the discriminating pathway project?

A

Primary somatosensory cortex

25
Q

Where does the undiscriminating pathway project?

A

Limbic system association cortices

26
Q

What is the role of the spinoreticular pathway?

A

Motor response and ascending arousal

27
Q

Describe the mechanism of wind up

A

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
Q

What is the purpose of wind up?

A

Priority salience
Protection from further injury
Memory

29
Q

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

A

Intensity of C fibre stimuli

30
Q

Describe pain modulation at the dorsal horn

A

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
Q

Name an endogenous substance that can provide descending analgesia

A

Enkephalin

32
Q

Why is the basis behind the high efficacy of opioids?

A

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

33
Q

Name 3 classes of endogenous opioids

A

Endorphins
Encephalins
Dynorphins

34
Q

Name 2 areas of the limbic system involved in pain

A

Cingulate gyrus - activated when we see others in pain

Insula - emotional, motivational and modulatory

35
Q

Give examples of persistent neuropathic pain

A

Causalgia
Phantom limb pain
Carpel Tunnel Syndrome
Peripheral neuropathy

36
Q

What is allodynia?

A

Painful reaction to non-noxious stimuli like light touch

37
Q

What is summation?

A

Repeated low innocuous stimuli causing increasing intensity of response

38
Q

What are dysesthesias?

A

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

39
Q

What causes central maladaption?

A

Increase in NMDA receptors

Descending modulation of inhibitory interneurons leading to reduced inhibition of WDR

40
Q

What is central maladaption?

A

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

41
Q

What is the proposed cause of headache?

A

Irritation of venous sinuses, meninges and capillaries

42
Q

Why do you get a headache after excessive alcohol consumption?

A

Alcohol irritates meninges

Dehydration

43
Q

Why does low CSF cause headache?

A

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

44
Q

Describe the mechanism of referred pain

A

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
Q

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

A

NA

46
Q

Which NT does the PVN and raphe nucleus release?

A

5-HT

Neurophysiology (17 decks)

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