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The Nervous System: Physiology > Physiology and Pathophysiology of Pain > Flashcards

Physiology and Pathophysiology of Pain Flashcards

1
Q

Define pain

A

An unpleasant sensory and emotional experience which we primarily associate with tissue damage
It is not a stimulus but a final product of compact information processing network

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2
Q

How is tissue damage detected

A

By specialised transducers with nociceptors connected to A delta and C primary afferent fibres

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3
Q

What is the function of A delta and C primary afferent fibres

A

Free nerve endings that conduct pain as first order neurone from peripheral nerve to the spinal cord

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4
Q

how are nerve fibres classified

A

Based on the diameter and conduction velocity

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5
Q

How are A delta fibres classified

A

Lightly myelinated

Medium diameter

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6
Q

What are A delta fibres responsible for

A

Fast pain
First pain
Sharp pain

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7
Q

How are C fibres classified

A

Un-myelinated

Small diameter

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8
Q

What is the property of C fibres

A

Slow conductors

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9
Q

What is C fibres responsible for

A

Dull pain

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10
Q

What do A delta and C fibres respond to

A

Thermal
chemical
mechanical
Noxious stimuli

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11
Q

What is the pathway of the first order of neurones of A delta and C fibres

A

travel through peripheral nerves, through cell body in dorsal root ganglion and synapse in the spinal cord dorsal column

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12
Q

What are the 3 sensory neurones that receive input in the spinal cords dorsal horn

A

Nocioceptive specific
-receive input from C and A delta fibre

Low threshold
mechanoreceptive
-Receive input from A beta fibres

wide dynamic range -receive input from main A beta
-But respond to both noxious and non noxious stimuli via interneurones

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13
Q

What do the interneurones influence in the dorsal horn on the nociceptive fibres

A

Is where first order neurones synapse for nociceptive fibres so influence the projection of neurones and afferent input

as either inhibits or exhibits projection of neurones

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14
Q

When nociceptive fibres synapse in the dorsal horn and become second order neurone their axons continue as tracts, what is the major ascending tract for nociceptive fibres

A

Spinothalmic tract receives A delta and C fibres

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15
Q

What is the pathway of second order neurone noceceptive fibres

A

Follows spirothalmic tract and crosses over to contralateral side to either lateral or ventral spinothalmic tract then sends impulses to thalamus

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16
Q

What is the function of the lateral spinothalmic tracts

A

Conveys fast and slow pain

  • pain
  • temperature sensations
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17
Q

What is the function of the ventral spinothalmic tracts

A

Convey sensation of simple touch

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18
Q

Where does the lateral spinothalmic tract synapse in the thalamus

A

ventroposterior thalamic nuclei

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19
Q

Where does the ventral spinothalmic tract synapse in the thalamus

A

the medial thalamic nuclei

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20
Q

What is the purpose of synapsing in the thalamus

A

as acts as a second relay station which further connects
cortex
limbic system
brain stem

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21
Q

Where does pain perception occur

A

in the somatosensory cortex

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22
Q

the connection between different brain centres to perceive pain is seen as a pain matrix divided into

A

Lateral aspect of pain matrix

Medial aspect of pain matrix

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23
Q

What is the lateral aspect of the pain matrix composed of

A

Somatorsensory cortex

ventralposterioir nuclei of thalamus

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24
Q

What is the function of the lateral aspect the pain matrix

A

Is the sensory discriminative part of nocieoception

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25
Q

What is the medial aspect of the pain matrix composed of

A 
(limbic system)
amygdala 
hippocampus 
cigluate cortex insula 
prefrontal cortex
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26
Q

What is the function of the medial aspect of pain matrix

A

cause feedback and forward with brain stem centres, for affective emotional components as well as descending control of pain

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27
Q

What occurs once the lateral spinothalmic tract terminates in ventroposterior thalamic nuclei

A

nuceli primarily feeds into somatosensory cortex to facilitate the spatial temporal and intensity discrimination of painful stimuli

give pain perception

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28
Q

What occurs when the Ventral spinothalmic tract terminates in the medial thalamic nuclei

A

Projects to the cortical regions such as anterior cingulate and insular cortex as well as other parts of the limbic system

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29
Q

With the brains perception of pain, we involve learning via the limbic system

How do we know the limbic system is connected to behaviours

A

as behavioural state influence the firing in medial thalamus

30
Q

How does the anterior cingulate in the limbic system contribute to pain

A

may contribute to the affective component of pain experience and modulate the autonomic and motor components of pain.

31
Q

How do we respond to the pain

A

via a descending pathway from brain to dorsal horn through periaqueductal grey matter pathway

32
Q

What is the cause peripheral sensitisation

A

a subjective experience to changes in nociceptors

either by decreases threshold for response, or the range as which stimuli become noxious changes giving an exaggerated response

33
Q

What is three types of peripheral sensitisations

A

Hyperalgesia

allodynia

spontaneous pain

34
Q

What occurs in hyperalgesia

A

an exaggerated response to normal and supernormal stimuli, resulting i increased perception of pain or even perception of non noxious stimuli as noxiou

35
Q

When does hypergesia occur

A

Occurs when there is tissue injury and inflammation, and due to any stimulation thermal or mechanical

36
Q

What are the different types o hypergesia

A

Primary hypergesai - is hypergesis at the site of injury

Secondary hypergesia - hyergesia to the surrounding uninjured tissue

37
Q

What occurs in allodynia

A

is a decreased threshold for response,

due to increased response of neurone following normally non painful stimulation

38
Q

What is involved in allodynia

A

Both peripheral and central mechanism are involved

Peripheral changed occur in the nociceptors because of inflammatory mediators and inherent changes

39
Q

What occurs in spontaneous pan

A

spontaneous activity in nerve fibres mainly due to nerve injuries

40
Q

How and where does central sensitisation occurs

A

Response of second order neurones in the CNS to normal input in both noxious and non noxious

Happens at the level of the spinal cord and acts as a tandem

41
Q

What is the three main components in central sensitisation

A

Wind Up

Classical

Long tem potentiation

42
Q

What occurs in wind up central sensitisation

A

Wind-up is literally winding up the response to the input. So the wind-up happens only in neurons taking part in the synapses with primary afferent input, progressively increasing the response of the neurones

=homosynaptic activity dependant

43
Q

What is the length of wind up in central sensitisation

A

manifests over the course of stimuli and terminates with stimuli (activity dependant)

44
Q

What mediates the mechanism of wind up

A

Mediated by neurotransmitters
Substance P
CGRP

45
Q

What occurs in classical central sensitisation

A

Involves the opening of new synapses (silent nocieoceptors)

so the new synapses which were silent will receive input and record the nociceptors

= hetrosynpatic activity dependant plasticity

46
Q

What triggers classical central sensitisation and how long does it last

A

Occur with all stimuli but the intensity has to be strong to elicit this response,

so has immediate onset with appropriate stimuli and can outlast the initial stimuli duration

once activated, can be maintained even at low levels of ongoing stimuli

47
Q

What is an examples of classical central sensitisation

A

NMDA receptor activation by glutamate is known to trigger a series of chamges resulting in classical central sensitization

48
Q

What is a clinical result of classical central sensitisation

A

Secondary hyperalgesia

where the area surrounding the injury site is also painful and where the touch also becomes painful

49
Q

What occurs in long term potentiation central sensitisation

A

Involves mainly the activated synapses

Occurs primarily for very intense stimuli

the mechanism involves both AMPA and NDMA receptor activation by glutamate

50
Q

Suprasegmental central sensitisation can clinically result in

A

Fibromyalgia

chronic wide spread pain

painful physical symptoms of depression/anxiety

51
Q

Explain gat control theory on pain

A

The gate control theory of pain asserts that non-painful input closes the “gates” to painful input, which prevents pain sensation from traveling to the central nervous system. Therefore, stimulation by non-noxious input is able to suppress pain.

52
Q

What opens the gate in gate control theory

A

The “gate” is opened by the activity of pain signals traveling up small nerve fibers

53
Q

what closes the gate in gate control theory

A

closed by activity in larger fibers or by information coming from the brain

54
Q

How do we control pain

A 
through descending
Peraqueductal grey (PAG) rosteroventromedial medulla (RVM) complex that exhibits gate theory control
55
Q

What is PAG

A

is the primary control center for descending pain modulation. It has enkephalin-producing cells that suppress pain in a noadrengeric system

56
Q

How does PAG exhibit gate control theory

A

The descending pathway, activates enkephalin-releasing neurons that project to the raphe nuclei in the brainstem and release serotonin

serotonin then descends to the dorsal horn of the spinal cord where it forms excitatory connections with the “inhibitory interneurons”

the activated interneurons inhibit incoming C and A-delta fibers activation of the second-order neuron that is responsible for transmitting the pain signal up the spinothalamic tract to the ventroposteriolateral nucleus (VPL) of the thalamus

The nociceptive signal was inhibited before it was able to reach the cortical areas that interpret the signal as “pain”

57
Q

What is the function of the rostral ventral medulla

A

sends descending inhibitory and excitatory fibers to the dorsal horn spinal cord neurone

so preceding nociceptive input or inhibiting nociceptive input

58
Q

Characteristics of acute pain

A

Physiological

presence of noxious stimuli

severe protective function

usually noceioceptive

usually obvious tissue damage

increased nervous system activity

pain resolves upon healing

59
Q

characteristics of chronic pain

A

Pathological

presence of noxious stimuli is not essential

does not serve any purpose - usually no protective function

nociceptive, neuropathic or mixed

pain for 3- 6months of more

pain beyond period of healing

degrades health and function

60
Q

Define noceioceptive pain

A

A sensory experience that occurs when specific peripheral sensory neurones (nociceptors) respond to noxious stimuli

61
Q

Characteristics of nociceptive pain

A

Painful region is typically localised t the site on injury
often

described as throbbing, aching or stiffness

Usually time limited and resolves when damaged tissue heals

response to conventional analgesics

62
Q

Define neuropathic pain

A

pain initiated or caused by a primary lesion or dysfunction in somatosensory nervous system

63
Q

Define characteristics of neuropathic pain

A

The pain region may not necessarily be the same as the sit of injury

Mostly always a chronic condition

Poorly responds to conventional analgesics

64
Q

Examples of neuropathic pain

A

postherpeutic neuralgia PHN

Post stroke pain

65
Q

Examples of noceoceptive pain

A

Acute

  • bone fracture
  • burns
  • brusises

chronic
- osteoarthritis

66
Q

What does treatment of pain depend upon

A

Location pathway point of pain

67
Q

What is the treatment If pain is due to transduction pathway

A

NSAIDS
ice
Rest
LA blockers

68
Q

What is the treatment If pain is due to Transmission pathway

A

Drugs:
opiods
anticonvulsants

Surgery:
-DREZ
(creates an opening in the spine and expose the spinal cord to asses the dorsal nerve route)

  • Cordotomy
    (Cutting selected nerves disables pain-conducting tracts in the spinal cord, effectively blocking pain sensation)
69
Q

What is the treatment If pain is due to perception pathway

A 
Education 
Cognitive behavioural therapy 
Distraction 
Relaxation 
Grader motor imagery 
Mirror box therapy
70
Q

What is the treatment If pain is due to descending modulation pathway

A

Placebos

Drugs:
opioids
antidepressants

Surgery:
cord stimulation

The Nervous System: Physiology (15 decks)

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