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NEURO > Physiology and pathology of pain > Flashcards

Physiology and pathology of pain Flashcards

1
Q

what is pain

A

an unpleasant sensory and emotional experience which we primarily associate with tissue damage or describe in terms of such damage or both

NOT A STIMULUS

final product of complex-information processing network

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2
Q

what is the brief pathway of pain

A

Step 1. Periphery

  • Detection
  • Transmission to spinal cord (first order neurons)

Step 2. Spinal cord

  • Processing
  • Transmission to brain (Thalamus) (second order neurons)

Step 3. Brain
- Perception, learning, response

Step 4. Modulation
- Descending tracts

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3
Q

what is nociception

A

the detection of tissue damage by specialised transducers connected to A-delta and C fibres

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4
Q

what are the structure and function of nociceptors

A

free nerve endings of A-delta and C fibres

respond to thermal, chemical and mechanical noxious stimuli

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5
Q

where are the primary afferent/1st order neurons for pain found and where do they synapse

A

cell body in dorsal root ganglion

synapse at spinal cord

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6
Q

what are the 4 sensory primary afferents and what are their characteristics

A

Aa + AB

  • myelinated
  • large diameter
  • proprioception, light touch

Adelta

  • lightly myelinated
  • medium diameter
  • heat, pain - fast

C

  • unmyelinated
  • small diameter
  • innocuous temp, pain - slow
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7
Q

what is the different between A-delta and C pain primary afferents

A

A-delta

  • fast pain
  • the immediate sharp pain

C

  • slow pain
  • later dull pain

e. g. someone pinches you
- immediate sharp pain - A-delta

  • as the sharp pain fades and transforms into a dull pain - C fibres
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8
Q

what neurons receive input from first order synapses and where are they found

A

Nociceptive specific - input from A-delta and C

Low Threshold Mechanoceptive - input from Aa

Wide Dynamic Range - Ab and interneurons

found in the spinal dorsal horn

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9
Q

what is the major ascending tract for nociception

A

lateral spinothalamic tract

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10
Q

where does the lateral spinothalamic tract go to

A

thalamus - acts as a second relay station

ventroposterior thalamic nuclei

medial thalamus

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11
Q

where does the thalamus connect to

A

cortex
limbic system
brainstem

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12
Q

where does pain perception occur

A

somatosensory cortex

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13
Q

where is the affective and emotional component of pain as well as the descending control of pain located

A

brainstem centres

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14
Q

what is the descending pathway for pain

A

brain - dorsal horn

through peri aqueductal grey matter

noradrenergic system

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15
Q

what does the descending pathway usually do to the pain signal

A

decreases it

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16
Q

what is hyperalgesia

A

the increased perception of pain or the perception of non-noxious stimuli as noxious

caused by an exaggerated response to normal and supernormal stimuli

happens when there is tissue injury or inflammation

17
Q

what is the difference between primary and secondary hyperalgesia

A

primary - hyperalgesia occurring at the site of injury

secondary - hyperalgesia occurring in the surrounding uninjured tissue

18
Q

what is allodynia

A

decreased threshold for response to pain

i.e. light touch perceived as painful

19
Q

how does spontaneous pain occur

A

spontaneous activity of the nerve fibres - mainly during nerve injury

20
Q

what is the gate control theory of pain

A

Adelta/C fibres excite projection neurons
= pain

Ab fibres excite inhibitory interneurons

inhibitory interneurones inhibit the projection neurons
= decreased perception of pain

21
Q

what is central sensitisation and what are the components

A

the response of second order neurons in the CNS

acts at the level of the spinal cord

  1. wind up
  2. classical
  3. long term potentiation
22
Q

what occurs in wind up sensitisation

A

involves only activated synapses

progressively increases response of neurons - to make the area more sensitive

only over the course of the stimulus - terminates with the stimulus

23
Q

what occurs in classical sensitisation

A

the opening up of new synapses (silent nociceptors) if intensity strong enough

allows for secondary hyperalgesia (surrounding area) and can outlast initial stimuli duration

once activated can be maintained by low intensity stimuli

24
Q

what occurs during long term potentiation

A

involves mainly activated synapses

occurs primarily for very intense stimuli

strengthening of synapses

25
Q

what are the characteristics of acute pain

A

<1 month

obvious tissue damage

increased nervous system activity

resolves upon healing

serves a protective function

26
Q

what are the characteristics of chronic pain

A

> 3-6 months

beyond expected period of healing

no protective function

degrades health and function

27
Q

what are some of the difference between acute and chronic pain

A

acute

  • physiological
  • noxious stimuli
  • serves protective function
  • usually nociceptive

chronic

  • pathological
  • noxious stimuli not essential
  • does not serve a purpose
  • nociceptive and/or neuropathic
28
Q

what is nociceptive pain

A

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

eg fracture, burns, bruises

29
Q

what are the characteristics of nociceptive pain

A

localised at site of injury

throbbing, aching, stiffness

time limited, resolves when damage heals

can be chronic - e.g. osteoarthritis

tends to respons to conventional analgesics

30
Q

what is neuropathic pain

A

Pain initiated or caused by a primary lesion or dysfunction in the somato-sensory nervous system

31
Q

what are the characteristics of neuropathic pain

A

pain may not be in the region of the site of injury

pain occurs in the neurological territory of the affected structure - e.g. nerve, root, spinal cord, brain

almost always chronic

responds poorly to conventional analgesics

32
Q

what are transduction associated pain reliefs

A

transduction = when peripheral terminals of nociceptive C fibers and A-delta fibers are depolarized stimuli

NSAIDS
Ice
REST
Local anaesthetic blocks

33
Q

what are transmission associated pain reliefs

A

transmission = impulse from the spinal cord to the brain stem and thalamus via nociceptive ascending pathways

Nerve blocks
Drugs - opioids
Surgery - DREZ, cordotomy

34
Q

what are perception of pain reliefs

A 
Education 
Cognitive behavioural therapy
Distraction
Relaxation
Graded motor imagery
Mirror box therapy (eps in phantom limb pain)
35
Q

what are descending modulation pain reliefs

A

placebos
drugs - opioids, antidepressants
surgery - spinal cord stimulation

NEURO (51 decks)

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