Case 2 - Overview of Pain

Question 1

what is pain

Answer 1

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

Question 2

what is nociception

Answer 2

noxious (toxic) stimulus that can become noxious with prolonged exposure. process though which peripheral pain receptors transit information about current tissue damage centrally as pain.

Question 3

what is a nociceptor

Answer 3

receptor in end organ that detects biochemical changes associated with current or potential tissue damage

Question 4

what is hyperalgesia

Answer 4

exaggerated response to noxious stimuli

Question 5

what is allodynia

Answer 5

sensation of pain in response to an innocuous stimulus

Question 6

what is nociceptive pain

Answer 6

pain in response to actual or potentially harmful stimulation. often described as aching and localised. aggravated by movement

Question 7

what is neuropathic pain

Answer 7

nerve injury or impairment that is associated with allodynia. often described as shooting or radiating. independent of movement

Question 8

diagram showing types of pain

Question 9

when do free nerve endings develop

Answer 9

7 weeks

Question 10

when is the hormonal stress response to pain developed

Answer 10

18 weeks

Question 11

when are thalamic projections into the somatosensory cortex developed

Answer 11

23-30 weeks

Question 12

when are haemodynamic and behavioural reactions to painful stimuli developed

Answer 12

26 weeks

Question 13

what are the 4 phases of pain pathways

Answer 13

1. transduction
2. transmission
3. modulation
4. central perception

Question 14

what is the first step in the nociceptive process

Answer 14

thermal, mechanische or chemical stimuli of noxious intensity come into contact with a tissue

Question 15

examples of inflammatory mediators from injured tissues

Answer 15

• globulin
• protein kinases
• arachniodonic acid
• nerve growth factor
• histamine
• substance P

Question 16

what is transduction

Answer 16

when the inflammatory mediators stimulate transducer channels which leads to initiation of receptor potentials

Question 17

what do receptor potentials evoke

Answer 17

action potentials in sensory nerve fibres

Question 18

what is transmission

Answer 18

when action potentials are carried as affect signals via sensory nerve fibres to the dorsal root ganglia and dorsal horn of the spinal cord

Question 19

what is modulation

Answer 19

when the signal is transmitted up the spinal cord to the brain stem and thalamus where significant processing may occur

Question 20

what is central perception

Answer 20

the signal finally reaches the somatosensory cortex.

Question 21

what is the amygdala involved in

Answer 21

the emotional and affective response to pain and pain modulation

Question 22

what is the hypothalamus involved in

Answer 22

the neuroendocrine corticotropin response to pain

Question 23

what is the periaqueductal gray matter involved in

Answer 23

key centre for pain modulation, involved in aversive and defensive pain behaviours

Question 24

what is the basal ganglia involved in

Answer 24

the cognitive, affective and discriminative aspects of pain perception

Question 25

what is the cerebral cortex involved in

Answer 25

it is the ultimate site of pain perception, potential for conscious activation of descending pathways for pain modulation.

Question 26

what are pain signals modulated by

Answer 26

endogenous opuoid peptides - endophines

Question 27

where are these pain signals modulated

Answer 27

- spinal cord - dorsal root ganglia - midbrain periaqueductal gray

Question 28

where does the mechanism of the modulation of pain occur

Answer 28

the descending inhibitory pathways

Question 29

what are the mechanisms of action of endogenous opioid peptides:

Answer 29

- activation of mu, kappa and delta opioid receptors leading to decreased presynaptic calcium influx which leads to decreased release of glutamate and SP - increased K+ conductance in dorsal horn neurones

Question 30

diagram showing the pathway of pain

Answer 30

Question 31

what are the three types of afferent nerve fibres

Answer 31

Type A, Type B, Type C

Question 32

describe type A fibres

Answer 32

large and myelinated fast conducting

Question 33

what are A-alpha fibres

Answer 33

primary receptors of the muscle spindle and Golgi tendon organ

Question 34

what are A-beta fibres

Answer 34

afferent axon with largest diameter. secondary receptors of the muscle spindle that contribute to cutaneous mechanoreceptors perceive light touch and or moving stimuli

Question 35

what are A-delta fibres

Answer 35

free nerve endings that conduct stimuli related to pressure and temperature

Question 36

what is the conduction speed of A-delta fibres

Answer 36

20m/sec

Question 37

describe type B fibres

Answer 37

midsized, thinly myelinated fibres responsible for autonomic information

Question 38

describe C fibres

Answer 38

unmyelinated nociceptor slow fibres conduction speed is approx 2m/sec repsons to combinations of thermal, mechanical and chemical stimuli

Question 39

what is rexed laminae

Answer 39

organised somatosensory and motor map laid out in the spinal cord of each spinal segment. different types of sensory nerves and the corresponding information they carry are organised so as to synapse in specific territories in the dorsal horn known as laminae

Question 40

what are the 10 different laminae

Answer 40

Receives and relays noxious and thermal stimuli Receives and relays noxious and non noxious physical stimuli and is involved In pain modulation Receives and relays physical stimuli related to light touch and proprioception Receive and relays non noxious physical stimuli Receives and relays noxious stimuli and is involved in pain modulation Received and relays information involved in spinal reflexes and proprioception Receives and relays information related to visceral function and noxious stimuli Receives and relays information related to visceral function and noxious stimuli Receives and relays information relayed to motor control Centrally located; where sensory and motor neurones cross before ascending/descending and where some degree of interneuronal cross-talk takes place

Question 41

what happens with these laminae in pathologic conditions

Answer 41

there can be abnormal rearrangement of sensory inputs that contributes to the development of central sensitisation and other manifestations of chronic pain

Question 42

ascending pathway of pain neurones

Answer 42

- nociceptors - neurone cell bodies - 2nd order neurones - thalamus

Question 43

describe nociceptors

Answer 43

receptors in the periphery respond to heat, intense cold, mechanical distortion, changes in pH and chemical irritants

Question 44

describe neurone cell bodies:

Answer 44

the cell bodies are first order neurones located in the dorsal horn and dorsal root ganglia of the spinal grey matter.

Question 45

what are the main neurotransmitters released by primary afferents

Answer 45

glutamate, SP and CGRP

Question 46

describe the 2nd order neurones

Answer 46

after synapsing in the spinal cord, the 1st order neurones project to 2nd order neurones 2nd order neurones cross the midline at the anterior white commissure These neurones then ascend to the thalamus via the contralateral spinothalamic tract, carrying both pain and temperature sensations

Question 47

describe the thalamus

Answer 47

from the thalamus, the stimulus is sent to the somatosensory cerebral cortex via fibres in the posterior limb of the internal capsule Other thalamic neurones project to areas of the cortex associated with emotional responses

Question 48

what is the descending pathway of pain

Answer 48

the hypothalamus and cortical regions proves painful stimuli and signals for the release of inhibitory mediators and hormones that make pain suppression more effective = pain modulation.