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BDS1 BAMS: Locomotor System > Pain and Nociception > Flashcards

Pain and Nociception Flashcards

1
Q

What is pain?

A

An unpleasant sensory and emotional experience associated with actual or potential tissue damage and described in terms of such damage

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2
Q

Which nerve fibres mediate nociceptive pain?

A

Adelta and C fibres
Adelta = sharp stabbing pain
C = dull, aching pain

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3
Q

What is the adaptive/biologically useful role of noiceptive pain?

A

Protective function

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4
Q

When is noiceptive pain elicited?

A

When intense/noxious stimuli threaten to damage normal tissue

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5
Q

What is nociceptive pain characterised by?

A

High threshold and limited duration

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6
Q

What are the 2 types of clinical pain?

A

Acute and chronic clinical pain

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7
Q

Describe acute clinical pain

A

Acute clinical pain results from soft tissue injury or inflammation. Serves as a protective function

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8
Q

Describe chronic clinical pain

A

A sustained sensory abnormality > 3 months. Result of an ongoing peripheral pathology e.g. chronic inflammation, peripheral nerve injury. Pain is maladaptive -> offers no survival advantage . Pain induction might be spontaneous or evoked

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9
Q

What is tactile allodynia?

A

Painful sensation to a previously innocuous stimulus

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10
Q

How many pairs of nerves are in the cervical segment of the spinal cord?

A

8

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11
Q

How many pairs of nerves are in the thoracic segment of the spinal cord?

A

12

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12
Q

How many pairs of nerves are in the lumbar segment of the spinal cord?

A

5

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13
Q

How many pairs of nerves are in the sacral segment of the spinal cord?

A

5

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14
Q

How many pairs of nerves are in the coccygeal segment of the spinal cord?

A

1

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15
Q

How many spinal cord segments are there?

A

31

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16
Q

The location of pain can be useful in differential diagnosis. Why is the location of pain potentially misleading?

A
  • Referred pain
  • This is pain felt in one part of the body but the pathology is elsewhere
  • Pain tends to be referred to sites of common embryological origin
  • Referral due to a convergence of inputs in the CNS
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17
Q

Where does pain tend to refer from?

A

From an internal organ to a superficial area e.g. skin

Tends to be referred to sites of common embryological origin

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18
Q

Provide an example of referred pain

A

Ischaemic pain e.g. angina, can be referred to the left arm

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19
Q

What are pain receptor endings?

A

Free nerve endings

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20
Q

What type of fibres are cutaneous and subcutaneous mechanoreceptors?

A

ABeta afferents

21
Q

Nociceptor endings display sensitisation. What does this mean?

A

Nerve fibres have a set period of time that they are able to generate action potentials. Adapts to stimulus despite continuous tissue damage

22
Q

What is the pathway for nociception for the body (not the face)?

A

Spinothalamic pathway

23
Q

What is the pathway for nociception for the face?

A

Anterior (ventral) trigeminothalamic tract

24
Q

Describe the spinothalamic tract

A
  • Primary sensory neuron projects from the periphery to the dorsal horn of the spinal cord
  • 2nd order projection neuron projects from dorsal horn to the antero-lateral funiculus, then continues on to the spinal lemniscus in the thalamus.
  • 3rd order projection neuron: from thalamus to sensory cortex
25
Q

Describe the anterior (ventral) trigeminothalamic tract

A
  • Pain receptors: free nerve endings extend into the dentine
  • Free nerve fibres project via C or Adelta fibres in trigeminal nerve to spinal nucleus in the spinal cord
  • Synapse onto 2nd order projection neurons - send axons to opposite side of the body up through brainstem to thalamus
  • 3rd order projection neurons: from thalamus to the sensory cortex
26
Q

Briefly describe the spinothalamic tract

A
  • primary sensory neuron from the periphery projects to dorsal horn of the spinal cord (Adelta and C fibres)
  • 2nd order projection neuron projects from the dorsal horn to the antero-lateral funiculus and continues up the spinal cord, through the brainstem and synapses in the spinal lemniscus in the thalamus
  • 3rd order projection neuron projects from thalamus to sensory cortex
27
Q

Briefly describe the anterior (ventral) trigeminothalamic tract

A
  • primary sensory neuron from the tooth (free nerve fibres that project into dentine) - Adelta and C fibres
  • Synapses with 2nd order projection neuron in the spinal nucleus of the spinal cord
  • 2nd order projection neuron crosses over to opposite side of the body and continues up through the brainstem and to the thalamus where it synapses with 3rd order projection neuron
  • 3rd order projection neuron from thalamus to sensory cortex
28
Q

At which level do axons cross over to the opposite side of the body in the spinothalamic tract?

A

Level of the spinal cord (2nd projection neuron projects from the dorsal horn to the opposite side of the spinal cord (the antero-lateral funiculus) and continues up to the spinal lemniscus in the thalamus where it synapses with 3rd order projection neuron

29
Q

At which level do axons cross over to the opposite side of the body in the anterior (ventral) trigeminothalamic tract?

A

At the level of the spinal nucleus of the spinal cord

30
Q

What does the SCN9A gene encode?

A

The alpha-subunit of the voltage-gated Na+ channel, Nav1.7

31
Q

Where is the voltage-gated Na+ channel (Nav1.7) strongly expressed?

A

In nociceptive afferents (receptor endings)

32
Q

What does a mutation in the SCN9A gene (SCN9-/-) cause?

A

Loss of Nav1.7 function (voltage-gated Na+ channel) -> inability to experience pain, but sensory and motor tests normal

33
Q

What are some of the psychological factors that can affect pain perception?

A

Sex, age, cognitive level, previous pains, family, culture

34
Q

What are some of the situational factors that can affect pain perception?

A

Expectation, control, relevance

35
Q

What are some of the emotional factors that can affect pain perception?

A

Fear, anger, frustration

36
Q

What is the gate control theory of pain?

A
  • In-built systems help us control our perception of pain
  • e.g. rubbing hand following a slap, decreases pain
  • Noxious stimulus activates Adelta/C fibres -> projects along spinothalamic pathway
  • Side branch at the dorsal horn of spinal cord: rubbing hand activates the inhibitory interneuron population. Blocks activity of secondary neurons. Information not conveyed by spinothalamic pathway. Blocks pain perception
37
Q

Explain how to gate control theory of pain can block pain perception

A
  • Noxious stimulus activates Adelta/C fibres -> projects along spinothalamic pathway
  • Side branch at dorsal horn of spinal cord: rubbing hand will active inhibitory interneuron population. Blocks activity of secondary neuron. Information not conveyed spinothalamic pathway => blocks pain perception
38
Q

What is descending modulation of nociceptive input?

A
  • ‘Supraspinal loop’ contributes to the modulation of nociceptive afferent input
  • Serotonergic and noradrenergic descending projections from the periaquaductal grey (PAG) and medullary raphe nuclei
  • Direct inhibition of projection neurons and/or activation of enkephalin-containing interneurons reduces activity in nociceptive circuits
39
Q

Where do descending serotonergic and adrenergic neurons project from?

A

From the periaqueduct grey (PAG) and medullary raphe nuclei

40
Q

What do serotonergic and noradrenergic descending projections from the PAG and medullary raphe nuclei do in the ‘supraspinal loop’?

A
  • Direct inhibition of projection neurons and/or activation of enkephalin-containing interneurons
  • This reduces activity in nocieptive circuits
41
Q

What is the supraspinal loop also known as?

A

Descending modulation of nociceptive input

42
Q

What does the supraspinal loop do?

A

Contributes to the modulation of nociceptive afferent input

43
Q

What are the 5 cardinal signs of inflammation?

A

Rubor (redness), tumor (swelling), calor (heat), dolor (pain), loss of function

44
Q

What is the white reaction?

A
  • Red line where the stimulus has occurred = red reaction
  • Whitening of the skin = wheal (this region is oedematous/swollen). Surrounds the red line
  • Flare = reddened area surrounding the wheal
45
Q

Describe the triple response

A
  • K+ and prostaglandins released by tissue damage
  • Activators for receptive endings in noiceptive terminals
  • Plasma: releases bradykinins
  • Platelets: release serotonin
  • Spinothalamic pathway is activated
  • Receptive endings in skin also release CRGP and substance P
  • CGRP and Substance P activate local mast cells
  • Local mast cells degranulate and release histamine
  • Histamine acts on receptive nerve endings to reinforce that there is trauma within that region
  • CGRP also causes dilation of blood vessels (flare region)
  • Substance P causes extravasation and oedema (wheal region)
46
Q

Briefly describe the triple response

A
  • Red reaction (where the stimulus has been applied e.g. scratch on skin)
  • Wheal = whitening of skin, surrounds red line. Area is oedematous/swollen.
  • Flare = reddened area surrounding the wheal
  • Tissue damage released K+ and prostaglandins, plasma releases bradykinin, and platelets release 5-HT
  • Receptive endings in skin released CGRP and Sub P
  • CGRP and Sub P activate local mast cells, which release histamine. Histamine acts on receptive endings, reinforces that there is trauma in that region.
  • CGRP causes dilation of blood vessels (flare region)
  • Sub P causes plasma extravasation and oedema (wheal region)
47
Q

What is dermatographia?

A

Exaggerated triple response

48
Q

How do local anaesthetics work?

A
  • Block Na+ channels -> block generation at the source

- Can also get anaesthetics that interfere with other components of the spinothalamic pathway

BDS1 BAMS: Locomotor System (7 decks)

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