Peter's Physiology 7 - Pain and Thermosensation

Question 1

What is pain?

Answer 1

An unpleasant sensory and emotional experience, associated with actual tissue damage or described in terms of such damage (although pain may be perceived in the absence of tissue/ organ damage)

Question 2

What type of pain is a pin prick and visceral distension examples of?

Answer 2

Nociceptive (acute) pain

Question 3

What type of pain is sunburn and an inflamed wound examples of?

Answer 3

inflammatory (prolonged) pain

Question 4

What type of pain is IBS, fibromyalgia, arthritis, cancer and AIDs examples of?

Answer 4

Pathological (neurogenic) pain

Question 5

What are the specific peripheral primary sensory afferent neurones that are normally activated preferentially by intense stimuli (e.g. thermal, mechanical, chemical) that are noxious, or damaging?

Answer 5

Nociceptors

Question 6

Where are nociceptor cell bodies located?

Answer 6

in the dorsal root ganglia and trigeminal ganglia

Question 7

What type of primary afferent fibres are nociceptors?

Answer 7

A delta and C fibres (NB not all A delta and C fibres are nociceptors)

Question 8

What type of noxious stimuli do A delta fibres respond to?

What type of pain does this mediate?

Answer 8

Mechanical and thermal stimuli

First/ fast pain

Question 9

Which of A delta and C fibres are unmyelinated?

Answer 9

C fibres

A delta fibres are thinly myelinated

Question 10

what type of noxious stimuli do C fibres respond to?

What type of pain does this mediate?

Answer 10

All types of noxious stimuli - polymodal

Second/ slow pain

Question 11

What is the phrased used to describe the fact the rate of action potential discharge from nociceptors correlates with the intensity of the applied stimulus ?

Answer 11

Frequency coding

Question 12

What is another name for type I A delta fibres?

Answer 12

High threshold mechanoreceptors

Question 13

What are type 1 A delta fibres activated by?

Answer 13

Strong mechanical stimuli/ noxious heat (threshold >53 degrees C)

Question 14

What happens to type I A delta fibres in response to prolonged stimuli?

Answer 14

Sensitisation occurs - threshold for activation by heat or mechanical stimuli falls

Question 15

What do type II A delta fibres respond to?

Answer 15

Noxious mechanical stimuli and also noxious heat (threshold of 43-47 degrees C), sensitive to capsaicin

Question 16

Which type of A delta fibres mediate first pain to intense mechanical stimuli?

Answer 16

Type I

Question 17

Which type of A delta fibres mediate first pain to heat?

Answer 17

Type II

Question 18

What are the 4 sub-classes of C fibres?

Answer 18

C - MH
C - M
C - H
C - MiHi (silent)

Question 19

What do C - MH fibres respond to?

Answer 19

Noxious mechanical stimuli
Noxious heat (threshold 39 - 51 degrees C)

Question 20

What type of C fibres are sensitive to capsicain?

Answer 20

C-MH
C-H
C-MiHi

Question 21

Do C-MH fibres show sensitisation to repeated stimuli?

Answer 21

Yes

Question 22

What functions does C-MH fibres have?

Answer 22

Contributes to heat pain

Location of stimulus

Question 23

What type of stimuli do C-M fibres respond to?

Answer 23

Noxious mechanical stimuli

Question 24

What type of stimuli do C-H fibres respond to?

Answer 24

Noxious heat (threshold 42 - 48 degrees C)

Question 25

What function does C-H fibres mediate?

Answer 25

Heat hyperalgesia

Question 26

What does C-H fibres acquire in the context of inflammation?

Answer 26

Sensitivity to mechanical stimuli

Question 27

Describe the function of C - MiHi fibres?

Answer 27

Normally insensitive to both mechanical and heat stimuli but acquires sensitivity following sensitisation by inflammatory mediators

Question 28

What is released from the peripheral terminal of nociceptors?

Answer 28

Molecules that influence local tissue environment e.g. substance P causing vasodilation and extravasation of plasma proteins, calcitonin gene related peptide causing vasodilation)

Question 29

Where are primary afferent cell bodies located (apart from in the trigeminal system)?

Answer 29

In the dorsal root ganglia

Question 30

What is the name for the 10 layers of grey matter in the spinal cord which are defined by their cellular structure?

Answer 30

Laminae of rexed

Question 31

Which laminae of rexed do the primary afferent axons terminate in?

Answer 31

I - V

Question 32

What laminae of Rexed do nociceptive C- and A-delta fibres mostly terminate in?

Answer 32

Superficially in laminae I and II (also V for A-delta fibres

Question 33

What do nociceptive specific cells synapse only with in the spinal cord?

Answer 33

C and A-delta fibres

Question 34

What is the input to proprioeceptive cells in the spinal cord?

Answer 34

Only A-beta fibres

Question 35

What do wide dynamic range neurones receive input from in the spinal cord?

Answer 35

All 3 types of fibres (thus respond to a wide range of stimuli)

Question 36

Name the 3 divisions of the trigeminal nerve?

Answer 36

``` V1 = ophthalmic V2 = maxillary V3 = mandibular ```

Question 37

Where are soma of the trigeminal nerves located?

Answer 37

Trigeminal sensory ganglion

Question 38

Where do trigeminal nerve fibres carrying info about general tactile stimuli synapse onto second order neurones?

Answer 38

In the chief sensory nucleus

Question 39

Where do trigeminal nerve fibres carrying info about pain and temperature synapse onto second order neurones?

Answer 39

Spinal nucelus

Question 40

Where do second order neurones in the trigeminal system project to in the thalamus and via what?

Answer 40

Decussate and project via the trigeminal lemniscus to the ventroposteriomedial (VPM) nucleus of the thalamus

Question 41

Describe the route of third order trigeminal neurones from the thalamus?

Answer 41

Project via thalamocortical neurones to the cortex

Question 42

Primary neurotransmitter used in the neurotransmission between the primary afferent and second order neurone in the dorsal horn (or spinal nucleus of the TG system)?

Answer 42

Glutmate

Question 43

In the dorsal horn (or spinal nucleus of the TG system) what does activation of glutamate receptors on second order neurones cause?

Answer 43

Membrane depolarisation (fast e.p.s.p.), opening of voltage-gated Na+ channels, action potential

Question 44

In the dorsal horn (or spinal nucleus of the TG system) what the of receptors are activated by glutamate?

Answer 44

Primary postynapti AMPA receptors with NMDA receptor participation

Question 45

In the dorsal horn (or spinal nucleus of the TG system), apart from glutamate, what other neurotransmitters are involved? (particularly during high frequency stimulation)

Answer 45

Peptides (substance P and CGRP)

Question 46

In the dorsal horn (or spinal nucleus of the TG system) what does peptide release cause?

Answer 46

A slow and prolonged e.p.s.p.facilitating activation of NMDA receptors be relieving voltage-dependent block by Mg2+

Question 47

What are the names of the 2 distinct types of sensitisation of the nociceptive pathway following tissue damage?

Answer 47

Peripheral sensitisation | Central sensitisation

Question 48

What mediates peripheral sensitisation?

Answer 48

Nociceptors at the site of injury/ tissue inflammation

Question 49

What mediates central sensitisation?

Answer 49

An increase in CNS neurone activity and propeties

Question 50

What does peripheral sensitisation cause? | How? (2)

Answer 50

Primary hyperalgesia Reduced threshold Amplified response

Question 51

What does central sensitisation cause? | How? (2)

Answer 51

Secondary hyperalgesia and allodynia Recruitment of novel inputs to nociceptive pathways Abnormal processing of sensory input

Question 52

What is required for maintenance of peripheral sensitisation?

Answer 52

Ongoing peripheral pathology

Question 53

What type of sensitisation causes pain that persists after tissue healing?

Answer 53

Central sensitisation

Question 54

What type of sensitisation is the main cause of heat sensitivity?

Answer 54

Peripheral sensitisation

Question 55

What type of sensitisation is the main cause of mechanical sensitivity?

Answer 55

Central sensitisation

Question 56

Where does visceral pain originate from?

Answer 56

Nociceptors covering tissues or walls of hollow organs

Question 57

What type of stimulus cause visceral pain? (4) | What type of stimulus do not cause visceral pain? (2)

Answer 57

Stretching, twisting, inflammation and ischaemia | Not cutting or burning

Question 58

Describe visceral pain?

Answer 58

Poorly localised | Dull, aching, throbbing character

Question 59

What pathways do visceral afferents follow before entering the dorsal horn?

Answer 59

Sympathetic pathways

Question 60

What type of neurones do visceral afferents converge on in the spinal cord?

Answer 60

Spinothalamic neurones

Question 61

Along with visceral afferents, what also converges onto spinothalamic neurones in the spinal cord? What does this describe?

Answer 61

Skin afferents | Referred pain

Question 62

What laminae do visceral nocicpetors terminate in?

Answer 62

Laminae I and V

Question 63

What is referred visceral pain often associated with?

Answer 63

Autonomic features e.g. nausea, vomiting, sweating, pallor

Question 64

Dermatome of referred pain from gallbladder?

Answer 64

C4

Question 65

Dermatomes of referred pain from heart?

Answer 65

T1-5

Question 66

Character of viscerosomatic pain?

Answer 66

Sharp and well localised

Question 67

How does viscerosomatic pain occur?

Answer 67

When inflammatory exudate from a diseased organ contacts a somatic (body wall) structure e.g. parietal peritoneum

Question 68

What 2 tracts does the anterolateral system comprise of?

Answer 68

``` Spinothalamic tract (STT) Spinoreticular tract (SRT) ```

Question 69

How do second order nociceptor neurones ascend the spinal cord?

Answer 69

In the anterolateral system

Question 70

What type of nociceptive neurones are transmitted by the spinothalamic tract?

Answer 70

Fast fibre A-delta | WDR neurones

Question 71

Where do nociceptive projection neurones originating from lamina I (fast fibre Adelta pain) terminate?

Answer 71

Posterior nucleus of the thalamus

Question 72

Where do protection neurones originating from lamina V (WDR neurones) terminate?

Answer 72

Posterior and ventroposterior nucleus of the thalamus

Question 73

For pain perception (location, intesity) from the spinothalamic tract, what must occur?

Answer 73

Simultaneous firing in both pathways

Question 74

What type of neurones does the spinoreticular tract mostly transmit?

Answer 74

Slow C-fibre pain

Question 75

What do second order neurones within the spinoreticular tract connect with?

Answer 75

Reticular nuclei in the brainstem

Question 76

What are signals int he spinoreticular tract responsible for?

Answer 76

Autonomic responses to apin, arousal, emotional responses, fear of pain

Question 77

Which out of the spinothalamic pathway and the spinoreticular pathway are classified as slow and fast?

Answer 77

``` STT = fast SRT = slow ```

Question 78

In the spinothalamic tract, where are signals from the thalamus relayed to? By what?

Answer 78

Relayed by thalamuocrotical neurones to the primary sensorimotor cortices

Question 79

What does the spinothalamic tract act as? By doing what?

Answer 79

Acts as a warning system by signalling the exact location and severity of the injury and duration of pain Also analyses the features of the pain

Question 80

Where does the spinoreticular pathway signal to? | Via what?

Answer 80

Intralaminar nuclei of the thalamus indirectly through the brainstem reticular formation via reticulothalamic tracts Signals from the thalamus are then relayed by the thalamuocrotical neurones to limbic areas of the forebrain

Question 81

Is pain and nociception the same?

Answer 81

No - pain is awareness of suffering -> nociception may occur in the absence of pain and vice versa

Question 82

How can pain evoked by activity in nociceptors be reduced?

Answer 82

By simultaneous activity in LTMs (Abeta-fibres)