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pain and nociception Flashcards

1
Q

define pain

A

pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage

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2
Q

describe physiological responses to pain

A
  • increased HR
  • increased BP
  • increased RR
  • decreased gastric motility
  • decreased BF to viscera, skin and kidneys
  • nausea
  • pallor
  • dilated pupils
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3
Q

define pain threshold

A

the point at which a stimulus is perceived as pain

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4
Q

define pain tolerance

A

duration or intensity of pain that an individual will tolerate before initiation of overt pain response

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5
Q

situations that decrease ones tolerance to pain

A
  • repeated exposure
  • fatigue
  • anger
  • sleep deprivation
  • boredom
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6
Q

situations that increase ones tolerance to pain

A
  • alcohol consumption
  • medication
  • hypnosis
  • warmth
  • distracting activities
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7
Q

age and perception of pain

A

newborns = less sensitive to pain

children= lower threshold than adults

adults = threshold tends to increase with ageing

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8
Q

define analgesia

A

absence of pain in response to stimulation that would normally be painful

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9
Q

define anaesthesia

A

absence of ALL sensory modalities

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10
Q

define hyperalgesia

A

an increased response to a stimulus that is normally painful

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11
Q

define allodynia

A

pain due to a stimulus that is not normally painful

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12
Q

define nociception

A

the sensory process of detecting tissue damage

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13
Q

define noxious stimulus

A

a noxious stimulus is one that is due to an event potentially or actually damaging to body tissue

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14
Q

what are the four basic processes involved in nociception (the sensory process for detecting tissue damage)

A
  • transduction
  • transmission
  • perception
  • modulation
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15
Q

define nociceptors and 3 categories of noxious stimuli

A

nociceptors are the peripheral free nerve endings of primary sensory neurons reactive to noxious stimuli (high threshold)

stimuli

  • mechanical (pressure, swelling)
  • thermal (burn, scald)
  • chemical (excitatory NT, toxic substance)
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16
Q

characteristics of C pain fibres and receptor type

A
  • primary afferent fibres
  • small diameter
  • unmyelinated
  • slow conducting

receptor type = polymodal
-respond to more than one type of noxious stimuli

17
Q

characteristics of A-delta fibres and receptor type

A
  • primary afferent fibres
  • medium diameter
  • myelinated
  • fast conducting

receptor type =
- responds to noxious mechano-thermal stimuli over a certain intensity

18
Q

difference in pain quality between C fibres and A-delta fibres

A

C fibres

  • diffuse
  • dull
  • burning
  • aching
  • referred to as slow or second pain

A-delta fibres

  • well-localised
  • sharp
  • stinging
  • pricking
  • referred to as fast or first pain
19
Q

describe the process of transduction

A

sensory cells convert external painful stimuli into electrical signals (AP)

20
Q

describe the process/pathway of transmission

A

primary afferents -> DH -> brain stem -> thalamus -> sensory cortex

nociceptor excitation is conducted to the sensopry cortex via a combination of electrical (AP) and chemical (NT)

21
Q

what are the 2 main classes of dorsal horn cells (secondary order neurons)

A
  1. nociceptive specific (rexed lamina 1 & 2)
    - respond to only noxious stimuli: C & A-delta fibers
  2. wide dynamic range (rexed lamina 5)
    - respond to both painful & non-painful fibers
22
Q

describe endogenous opioids

A

substances produced in the body that can activate opioid receptors
e.g. endorphins

23
Q

perception of pain

A

is multi-dimensional

reticular system:
-autonomic & motor response to pain

limbic system:
-emotional & behavioral responses

somatosensory cortex
-perception & interpretation of sensations

24
Q

modulation of perception of pain

A

there is a difference between objective reality and subjective response to pain. Explaining that there is a mechanism in the body that MODULATES pain perception

25
Q

pain dampening

A

down-regulation

  1. segmental inhibition
  2. descending inhibitory nerve system
26
Q

gate control theory

A

based on the premise that a gate, located in the dorsal horn of the spinal cord, modulates the afferent nerve impulses

implies that a non-painful stimulus can block the transmission of a noxious stimuli

27
Q

3 input variables that affect the gate control theory

A
  1. A-delta and C fibers - open gate
  2. A-beta fibers that carry messages of light touch - close gate
  3. messages from the brain - open/close
28
Q

the mechanism involved in keeping the ‘gate’ closed

A

there are special inhibitory interneurons in the spinal cord which keep the gate closed.
these neurons make a pain-blocking endogenous opioid called enkephalin
this is an opioid-like which blocks NT release from C and A-delta fibers and this keeps the gate closed

29
Q

give examples that open and close the ‘gate’

A

open

  • extend of injury
  • anxiety
  • boredom

close

  • medication
  • relaxation
  • distraction
  • positive emotions
30
Q

describe the process and different fibers involved in bumping your head

A
  1. initial trauma activates A-delta fibres
  2. eventually C fibres
  3. rubbing area stimulates A-beta fibres which activates the DH to close gate
31
Q

define the term windup

A

increased AP output from the DH cells in response to sustained low Hz input from nociceptive afferents via C fibres to the DH neurones

32
Q

mechanism of windup

A

receptor on DH neurons are stimulated by C fibres due to a continuous stimuli for an extended period of time. causing increased Ca2+ influx into DH neurons. This leads to pathophysiologic changes by lowering threshold of receptors. thus becoming more sensitive to inputs resulting in hyperalgesia or allodynia

33
Q

types of pain

A
  • nociceptive (tissue damage)
  • neuropathic (damage to nerve fibers)
  • inflammatory
  • referred
34
Q

nociceptive pain pathway

A
  1. tissue damage causes release of mediators e.g. OG, serotonin, ACh
  2. mediators stimulate pain receptors
  3. process of transduction, transmission, perception and modulation takes place
35
Q

describe the 2 types of inflammation

A

non-neurogenic

  • release of inflammatory substances from BVs & CTs
  • e.g. histamine, PG, cytokines

neurogenic

- release of neuropeptides from C-fibre terminals
- e.g. noradrenaline, substance P
36
Q

describe the non-neurogenic inflammatory pathway

A
  1. tissue damage
  2. inflammatory mediators (e.g. mast cell, macrophages) release substances
  3. substances sensitive receptors and lower threshold
  4. more pain felt

= peripheral sensitisation
-primary hyperalgesia

37
Q

neuronal plasticity

A

changes to the neuronal anatomy & physiology in DR

due to prolonged pain with no treatment

Very difficult to treat

38
Q

enkephalin

A

is an endogenous opioid - inhibitory interneuron

blocks neurotransmitter release from C and A-delta fibers
-keeps gate closed

neuro (20 decks)

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