Pathophysiology of Pain Flashcards

1
Q

Define Pain

A

An unpleasant sensory experience associated with tissue damage
It is not a stimulus, it is a final interpretation of nociception in the brain

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2
Q

What nerve fibres carry nociception?

A

Adelta - Small Myelinated - Fast Pain

C - Unmyelinated - Slow/delayed Pain

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3
Q

What are Rexed Layers?

A

Rexed divided the spinal cord into 10 layers based on their cytoarchitecture

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4
Q

What are the 3 types of neurons in the spinal cord and what rexed layer are they found?

A

Low Threshold Mechanoreceptive Neurons - Layer 3/4 - Abeta fibres

Nociceptive Specific Neurons - Layer 1/2 - Adelta/C fibres

Wide Dynamic Range (WDR) neurons - Layer 5 - respond to both noxious and non-noxious stimuli

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5
Q

What tracts do pain fibres travel up?

A

Spinothalamic Tract, divided in two:

  • Lateral STT carries fast and slow pain + Temp
  • Anterior STT Carries crude touch

The STT arises in Rexed LAmina 2 & 5

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6
Q

Where do the fibres in the Spinothalamic Tract go?

A

Ventral STT -> Medial Thalamic Nuclei -> Limbic System (emotional response to pain & desc. control)

Lateral STT -> Ventroposterior Thalamic Nuclei -> Primary Somatosensory cortex (spatial & intensity discrimation of pain)

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7
Q

Explain the descending pathways of pain?

A

Periacqueductal grey (PAG) matter activates a descending noradrenergic system to the dorsal horn where it gates pain using endogenous opioids

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8
Q

What are the categories of pain sensitization?

A

Peripheral
Segmental Central
Suprasegmental Central

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9
Q

What are the types of peripheral pain sensitization?

A
  • Hyperalgesia (Increased neuronal response to pain signals)
  • Spontaneous Pain (Spontaneous activity in nociceptive nerve fibres)
  • Allodynia
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10
Q

What is Allodynia?

A

Sensitization of the nociceptors themselves

So the nociceptor threshold lowers causing it to trigger signals for stimuli that arnt normally considered noxious

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11
Q

What is hyperalgesia?

A

Exaggerated response of the neurons to already painful stimuli
I.e. the stimulus-response curve shifts left, your perception of pain increases

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12
Q

What are the types of Segmental Central Sensitization?

A

Wind up - Increased response through the 1-2nd order synapse

Classical - Opening up of new synapses

Long-Term Potentiation

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13
Q

How does Wind up sensitization work?

A

Homosynaptic Activity-Dependant Progressive increase in Neuronal Response.

Over the course of the stimulus the active synapses become more responsive, this terminates with the stimulus

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14
Q

How does Classical Sensitization work?

A

If the stimulus is intense enough then it opens up new synapses, thus increases the active pain fibres.

Can outlast the stimuli as maintainable by a low intensity stimulus

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15
Q

How does longterm potentiation work?

A

We dont really know but it involved already activated synapses (unlike classical) and very intense stimuli

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16
Q

Pain conditions such as fibromyalgia and the painful symptoms of depression are caused by what?

A

Its believed the pain is sourced from supra-segmental pain sensitization in the thalamus & Cortex

17
Q

Whats the difference between chronic and acute pain?

A

In acute pain theres usually obvious damage and the pain resolves with healing, Its serving a protective function. Nociceptive

In chronic pain it lasts beyond the period of healing, It has no protective function and actually degrades health and function. Nociceptive and/or Neuropathic

18
Q

Whats the difference between Nociceptive & Neuropathic pain?

A

Nociceptive:

  • Localised to site of injury
  • Throb/ache/stiff
  • Responds to conventional analgesics
  • May be chronic e.g. osteoarthritis

Neuropathic:

  • Causes by lesion or dysfunction of somatosensory nervous system
  • E.g. Neuroma caused by nerve damage, stroke or MS
  • Pain found at region supplied y nerve not necessarily region of injury
  • Almost always chronic
19
Q

What are the categories of pain management?

A
  • Transduction
  • Transmission
  • Perception
  • Descending Modulation
20
Q

Whats involved in pain management through Transduction?

A

NSAIDs
Ice
Rest
Local Anaesthetics

21
Q

What methods are there for pain management through transmission?

A
  • Nerve blocks e.g. General Aneasthetics
  • Drugs e.g. Opiods or Anticonvulsants
  • Surgery e.g. Cordotomy
22
Q

How do we manage perception of pain?

A
  • Cognitive Behavioral Therapy
  • Distraction
  • Relaxation
  • Education

Also for people with missing limb pain we can use Graded Motor Imagery & Mirror Box Therapy

23
Q

How do we control pain through descending modulation?

A
  • Placebos
  • Drugs e.g. Opiods and antidepressants
  • Surgery e.g. Spinal Cord Stimulation