pain and nociception

Question 1

define pain

Answer 1

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

Question 2

describe physiological responses to pain

Answer 2

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

Question 3

define pain threshold

Answer 3

the point at which a stimulus is perceived as pain

Question 4

define pain tolerance

Answer 4

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

Question 5

situations that decrease ones tolerance to pain

Answer 5

• repeated exposure
• fatigue
• anger
• sleep deprivation
• boredom

Question 6

situations that increase ones tolerance to pain

Answer 6

• alcohol consumption
• medication
• hypnosis
• warmth
• distracting activities

Question 7

age and perception of pain

Answer 7

newborns = less sensitive to pain

children= lower threshold than adults

adults = threshold tends to increase with ageing

Question 8

define analgesia

Answer 8

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

Question 9

define anaesthesia

Answer 9

absence of ALL sensory modalities

Question 10

define hyperalgesia

Answer 10

an increased response to a stimulus that is normally painful

Question 11

define allodynia

Answer 11

pain due to a stimulus that is not normally painful

Question 12

define nociception

Answer 12

the sensory process of detecting tissue damage

Question 13

define noxious stimulus

Answer 13

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

Question 14

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

Answer 14

• transduction
• transmission
• perception
• modulation

Question 15

define nociceptors and 3 categories of noxious stimuli

Answer 15

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)

Question 16

characteristics of C pain fibres and receptor type

Answer 16

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

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

Question 17

characteristics of A-delta fibres and receptor type

Answer 17

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

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

Question 18

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

Answer 18

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

Question 19

describe the process of transduction

Answer 19

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

Question 20

describe the process/pathway of transmission

Answer 20

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)

Question 21

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

Answer 21

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

Question 22

describe endogenous opioids

Answer 22

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

Question 23

perception of pain

Answer 23

is multi-dimensional

reticular system:
-autonomic & motor response to pain

limbic system:
-emotional & behavioral responses

somatosensory cortex
-perception & interpretation of sensations

Question 24

modulation of perception of pain

Answer 24

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

Question 25

pain dampening

Answer 25

down-regulation 1. segmental inhibition 2. descending inhibitory nerve system

Question 26

gate control theory

Answer 26

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

Question 27

3 input variables that affect the gate control theory

Answer 27

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

Question 28

the mechanism involved in keeping the 'gate' closed

Answer 28

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

Question 29

give examples that open and close the 'gate'

Answer 29

open - extend of injury - anxiety - boredom close - medication - relaxation - distraction - positive emotions

Question 30

describe the process and different fibers involved in bumping your head

Answer 30

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

Question 31

define the term windup

Answer 31

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

Question 32

mechanism of windup

Answer 32

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

Question 33

types of pain

Answer 33

- nociceptive (tissue damage) - neuropathic (damage to nerve fibers) - inflammatory - referred

Question 34

nociceptive pain pathway

Answer 34

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

Question 35

describe the 2 types of inflammation

Answer 35

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

Question 36

describe the non-neurogenic inflammatory pathway

Answer 36

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

Question 37

neuronal plasticity

Answer 37

changes to the neuronal anatomy & physiology in DR due to prolonged pain with no treatment Very difficult to treat

Question 38

enkephalin

Answer 38

is an endogenous opioid - inhibitory interneuron blocks neurotransmitter release from C and A-delta fibers -keeps gate closed