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202: Theme 2, Sensory inputs and motor outputs > Physiology of pain 1 > Flashcards

Physiology of pain 1 Flashcards

1
Q

Classifications of pain [3]

A

Nociceptive
- Due to functioning nociceptors

Inflammatory
- Due to response to inflammation

Neuropathic
- Response to injury of the nervous system

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2
Q

Nociceptors

  • Definition
  • Function
A

Primary sensory neurones that detect pain from

  • Skin
  • Muscles
  • Joints
  • Viscera
  • Meninges

Carry sensory information to dorsal root ganglia —> dorsal horn

Contains free nerve endings in the periphery [A-delta or C fibres]

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3
Q

A-alpha and A-beta sensory fibres

  • Myelination
  • Function
  • Diameter
  • Conduction velocity
A

Myelinated afferent nerve fibre

  • Detects light touch and proprioception
  • Large diameter
  • 30-75 m/sec
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4
Q

A-delta sensory fibres

  • Myelination
  • Function
  • Diameter
  • Conduction velocity
  • Response to pain
A

Thinly myelinated afferent fibres

  • Detects light touch, temperature and nociception
  • Medium diameter
  • 5-30 m/sec

Response to pain
- Sharp, prickling

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5
Q

C fibres

  • Myelination
  • Function
  • Diameter
  • Conduction velocity
  • Response to pain
A

Unmyelinated afferent nerve fibre

  • Detects temperature and pain [nociception]
  • Small diameter
  • 0.5-2 m/sec

Response to pain

  • Slow, dull ache
  • Burning
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6
Q

Meissner’s fibres

  • Type of fibre
  • Function
  • Location
A

A-beta fibres

Detects stoking and fluttering

Found in glabrous skin

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7
Q

Pacinian fibres

  • Type of fibre
  • Function
  • Location
A

A-beta fibres

Detects vibration, deep in glabrous skin

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8
Q

Merkel disc

  • Type of fibre
  • Function
  • Location
A

A-beta fibres

Detects pressure in glabrous skin

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9
Q

Ruffini fibres

  • Type of fibre
  • Function
  • Location
A

A-beta fibres

Detects stretch in hairy skin

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10
Q

Pain transduction

- Types of pain

A
  1. Fast sharp pricking
    - Localised
    - Activates reflex arcs
    - Not present in visceral pain
  2. Slow dull ache
    - Poorly localised
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11
Q

Factors that activate nociceptors [4]

A

Pressure

Heat/ cold [temperature]

Chemical

Tissue damage/ inflammation

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12
Q

Polymodal nociceptors

A

Responds to different types of sensory stimuli

  • Pressure
  • Temperature
  • Chemical

Most C-fibres nociceptors are polymodal

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13
Q

Pressure transduction

A

Mechanically sensitive ion channels

Specific channel still not known.

Acid sensing ion channels and TRPA1 are involved

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14
Q

Temperature transduction

A

Transient receptor potential family of channels

TRPV1- detects hot temperature

TRPM- detects cold temperature

TRPA 1- Detects very cold temperatures

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15
Q

Agonists for

  • TRPVI
  • TRPM
  • TRPA1
A

TRPV 1
- Chilli [capsaicin]

TRPM
- Menthol

TRPA 1
- Cinnamon

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16
Q

Central pain pathway

A

Ascends spinothalamic tract

First order neurones

  • Enter dorsal horn via tract of Lissauer
  • Synapse in substantia gelatinosa [lamina 1 + 2] with second order neurones
  • Release glutamate and substance p

Second order:

  • Crosses the dorsal horn at each level
  • Ascends anterolateral column to thalamus

Third order:

  • Projection into somatosensory cortex
  • Projection into insula and cingulate cortex
  • Activation of cortical regions [e.g limbic, prefrontal]
17
Q

Referred pain

A

Brain perceiving visceral pain as cutaneous

- Visceral and cutaneous nociceptors converge on the same second order neurones

18
Q

Sensory homunculus

A

The distribution of sensation in the somatosensory cortex

Lower body= medial cortex

Upper body= lateral cortex

19
Q

Spinothalmic tract projection in the somatosensory cortex

A

Encodes the sensory components

  • Location of pain
  • Modality of pain
20
Q

Spinothalmic tract projection in insula and cingulate cortex

A

Encodes the emotional components of pain

21
Q

Descending modulatory pathways

A

Modulation of spinothalamic tract activity, originating from the cortex

Cortex—-> Periaqueductal grey matter [midbrain]

Periaqueductal grey matter—-> Rostral ventromedial medulla [medulla]

22
Q

Inhibition of pain

A

Periaqueductal grey matter [PGM] excites rostral ventromedial medulla {RVM]
- Inhibits the spinothalamic tract

Serotonergic projection from RVM synapses onto inhibitory neurone in dorsal horn

NADR pathway is also parallel to this

23
Q

Endogenous opioid system

A

Act on inhibitory metabotrophic receptors
- Important in stress induced analgesia

Release site = from interneurones

  • Periaqueductal grey matter [midbrain]
  • Rostal ventromedial medulla [medulla]
  • Dorsal horn
24
Q

Chemicals that activate or modulate nociceptors in inflammatory pain [7]

A

ATP

H+

Serotonin/ 5-HT

Histamine

Bradykinin

Prostaglandin

Nerve growth factor

25
Q

ATP activation of nociceptors

A

Binds to purinergic receptors [P2X]

26
Q

H+ activation of nociceptors

A

Binds to acid-sensing ion channels

27
Q

Serotonin activation of nociceptors

A

Binds to 5-HT3 receptors

28
Q

Neurogenic inflammation

A

Activation of a branch of nociceptor axon = release of substance P and CGRP from another branch.

Release of the pro- inflammatory chemicals=

  • Vasodilation
  • Increased permeability
  • Activation of mast cells= release of histamines= more inflammation
29
Q

Pain hypersensitivity

A

Can occur as a result of inflammation
- Pain stimulus is perceived as more painful.

Examples:

  • Allodynia
  • Hyperalgesia
30
Q

Allodynia

A

Type of pain hypersensitivity

- Painful response to non-noxious stimuli

31
Q

Hyperalgesia

A

Typer of pain hypersensitivity

- Exaggerated pain response to noxious stimuli

32
Q

Peripheral sensitisation

  • Mechanism
  • Chemicals released
  • Examples
A

Mechanism for hyperalgesia

Inflammation/tissue damage = Increase in responsiveness of the peripheral ends of nociceptors

Release of:
- Bradykinin and NGF = reduction of threshold for TRPV-1

  • Prostaglandin = reduction of threshold of Na+ channels.

Example: after sunburn

33
Q

Bradykinin

- peripheral sensitisation

A

Activates TRPV-1
- Binds to metabotrophic G-protein

  • Activates protein kinase —–> phosphorylates TRPV1 = reduction of threshold for channel]

202: Theme 2, Sensory inputs and motor outputs (13 decks)

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