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MSK > Pain physiology > Flashcards

Pain physiology Flashcards

1
Q

What are the three classifications of pain?

A

Nocioceptive
Inflammatory
Pathological

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2
Q

What is the definition of pain?

A

An unpleasant sensory and emotional experience.

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3
Q

What are nocioceptors?

A

Peripheral primary specific sensory afferent neurones activated by intense noxious stimuli e.g. Chemical, thermal, mechanical etc.

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4
Q

Are nocioceptors first or second order neurones?

A

First order

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5
Q

What kind of neurones do nocioceptors relay information to and where are they?

A

Second order neurones in the CNS

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6
Q

Is nocioceptive pain adaptive or maladaptive?

Why?

A

Adaptive as it is an early warning system that detects and minimises contact with damaging stimuli.

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7
Q

Is nocioceptive pain high or low threshold?

A

High threshold, it is provoked only by intense stimuli.

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8
Q

What happens when a nocioceptor is activated by noxious stimuli?

A

It overrides other CNS activities and initiates a withdrawal reflex. It also initiates an emotional response that allows us to remember this and avoid the stimuli in future.

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9
Q

Is inflammatory pain adoptive or maladaptive?

A

It is adaptive and protective

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10
Q

What other two things can inflammatory pain result in?

A

Pain hypersensitivity and allodynia (innocuous stimuli now elicit pain)

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11
Q

What is the benefit of inflammatory pain?

A

Assists in healing of damages area by: discouraging physical contact and movement.

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12
Q

Is inflammatory pain high or low threshold?

A

Low threshold in order for tenderness to promote healing.

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13
Q

What is adaptive pain?

A

Helpful pain that will encourage behaviour that aids healing.

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14
Q

Is pathological pain adaptive or maladaptive?

A

Maladaptive, it has no protective function

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15
Q

What are the two categories of pathological pain?

A

Neuropathic and dysfunctional.

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16
Q

What is neuropathic pain?

A

Caused by damage or disease affecting the somatosensory nervous system.

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17
Q

What two things is pathological pain associated with?

A

Spontaneous pain and pain hypersensitivity.

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18
Q

What is dysfunctional pain?

A

A pain where there is no obvious neural lesion or inflammatory pain.

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19
Q

What causes congenital insensitivity to pain?

A

Rare condition resulting in loss of function mutations e.g. Missense in gene that encodes Na channels that are highly expressed in nocioceptive neurones

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20
Q

What are the symptoms of CIP?

A

Lip and tongue injury, bruises and cuts, multiple scars, bone fractures, joint deformity and premature mortality.

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21
Q

What are the two subtypes of nocioceptor?

A 
A delta (incomplete figure of 8 sign)
C-fibres
22
Q

What type of stimuli do A delta nocioceptors respond to?

A

Mechanical and thermal stimuli.

23
Q

Are A delta nocioceptors myelinated?

A

Yes but only thinly

24
Q

What type of pain do A delta nocioceptors mediate?

A

First or fast pain e.g. Stabbing prickling sensations.

25
Q

Are c fibres myelinated?

A

No they are unmyelinated so have slower conduction velocity.

26
Q

What type of stimuli do C fibre nocioceptors respond to?

A

All types of stimuli collectively.

27
Q

What type of pain do C fibres mediate?

A

Second or slow pain e.g. Burning, throbbing cramping aching sensations.

28
Q

How does a stimulus in sensory neurones illicit an action potential?

A

They open ion channels in the nerve terminal.

29
Q

What is the potential created by stimuli at a sensory nerve terminal called?

A

Depolarising receptor or generator potential.

30
Q

What affects the generator potential amplitude?

A

The intensity of the stimulus, the generators potential is graded to this.

31
Q

What effect does the generator potential amplitude have on the resulting action potential?

A

Action potential are triggered at a frequency proportional to the amplitude of the receptor potential.

32
Q

Where do nociceptor nerves enter the spinal cord?
Where are their cell bodies?
What happens to the after they enter the spinal cord?

A

Enter through the dorsal horn
Bodies in the dorsal root ganglion or trigeminal ganglion.
They cross over the spinal cord and ascend to brain up the anterior horn.

33
Q

What is a subset of C fibres that have afferent and efferent functions?

A

Peptidergic polymodal nociceptors.

34
Q

What peptides do afferent peptidergic polymodal nociceptors release in the dorsal horn?

A

Substance P and neurokinin A

35
Q

What substances do efferent peptidergic polymodal nociceptors release?

A

Inflammatory mediators e.g. Calcitonin gene-related peptide (CRGP), substance P etc.

36
Q

What can chemical release from efferent peptidergic polymodal nociceptors contribute to?

A

Neurogenic inflammation.

37
Q

What does release of substance P cause?

A

Vasodilation and extravasation of plasma proteins
Release of histamine from mast cells
Sensitises surrounding nociceptors

38
Q

What does CRGP do?

A

Induces vasodilation

39
Q

What stimuli can trigger release of chemicals from petidergic nociceptor efferents?

A

Tissue damage or inflammatory mediators.

40
Q

What is the primary transmitter released from the primary afferent in the dorsal horn?

A

Glutamate

41
Q

What is the name for the area in the dorsal horn where primary afferent axons terminate?

A

Laminae of rexed

42
Q

Where do nociceptive C and A delta fibres mostly terminate?

A

Superficially in laminae 1 and 2 (and also 5 for A delta)

43
Q

What do nociceptive specific cells synapse with?

A

C and Adelta fibres.

44
Q

What type of cells only receive input from Abeta fibres?

A

Proprioceptive

45
Q

What type of neurones receive input from C fibres Adelta and Abeta fibres?

A

Wide dynamic range neurones.

46
Q

Where do second order neurones ascend the spinal cord?

A

In the anterolateral system

47
Q

What does the anterolateral system in the spine mostly consist of?

A

The spinothalmic tract and the spinoreticular tract.

48
Q

What types of neurones does the spinothalmic tract project?
What lamina do they come from?
Where does it terminate?

A

Fast fibre Adelta neurones
Lamina 1
Posterior nucleus of the thalamus

WDR neurones
Lamina 5
Terminates in posterior and ventroposterior nucleus of the thalamus.

49
Q

What does pain proprioception require?

A

Simultaneous firing of both pathways in the spinothalmic tract

50
Q

What does the spinoreticular tract mostly transmit?

A

Slow C fibre pain neurones

51
Q

Where does the spinoreticular tract connect to in the brain?

A

Reticular nuclei in the brain stem (periaqueductal grey - PAG) and parabrachial nucleus (PBN)

52
Q

What responses to pain is the spinoreticular tract involved in?

A

Autonomic responses e.g. Emotional arousal, fear etc.

MSK (10 decks)

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