Physiology of Pain

Question 1

What is pain?

Answer 1

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

Question 2

What are the three forms of pain and are they adaptive or maladaptive

Answer 2

Nociceptive pain - adaptive
Inflammatory pain - adaptive
Pathological pain - maladaptive

Question 3

What is nociceptive pain

Answer 3

Acute pain that occurs immediately at the time of inury

Question 4

What is the purpose in nociceptive pain

Answer 4

Helps us limit damage to the body and avoid further damage

Question 5

What is inflammatory pain

Answer 5

More persistent pain that generally subsides after healing

Question 6

What is pathological pain?

Answer 6

Pain that persists after injury that has been resolved or arises out of the blue with no precipitating injury. It has outlived its biological purpose

Question 7

What type of pain is the most difficult to treat

Answer 7

Pathalogical pain

Question 8

What are nociceptors?

Answer 8

Specific peripheral primary sensory afferent neurones normally activated preferntially by intense stimuli (thermal, chemical or mechanical) that are harmful

Question 9

What do nociceptors do?

Answer 9

They are first order neurones that relay information to second order neurones in the CNS by chemical synaptic transmission

Question 10

Describe how noceiceptors work when exposed to an intense stimuli

Answer 10

The free nerve ending in the peripheral location senses the harmful stimuli and depolarisation occurs due to this. If the depolarisation is large enough, it triggers an action potential which then goes along the axon to the soma which then triggers the release of transmitter substances in the central terminal

Question 11

Nociceptive pain is high threshold. What does this mean?

Answer 11

It is provoked only by intense stimuli that activate nociceptors

Question 12

What does Nocicpetive pain overide

Answer 12

Most other ongoing activities of the nervous system

Question 13

Inflammatory pain is both adaptive and protective. True or False

Answer 13

True

Question 14

What causes inflammatory pain

Answer 14

Activation of the immune system in injury or infection

Question 15

What does pain hypersensitivity cause

Answer 15

Heightened sensitivity to noxious stimuli and allodynia (innocuous stimuli now elicit pain)

Question 16

How does inflammatory pain help the body to heal

Answer 16

It discourages physical contact and discourages movement

Question 17

What is required to alleviate suffering

Answer 17

Reduction in ongoing inflammation (rheumatoid arthritis)

Question 18

How do nerve cells in inflammatory pain become more sensitive

Answer 18

Due to the increase of inflammatory cells such as macrophages, mast cells, neutrophils and granulocytes in the affected area

Question 19

How does pathological pain arise?

Answer 19

It results from abnormal nervous system function - may be neuropathic or dysfunctional

Question 20

How do we describe what pathological pain is

Answer 20

Maladaptive with no protective function

Question 21

WWhat happens in the absence of pain?

Answer 21

Gross damage to the body

Question 22

Patients with congenital insensitivity to pain (CIP) may have what types of injuries?

Answer 22

Anything:
lip and tongue injury 
bruises and cuts 
multiple scars 
bone fractures 
joint deformity 
premature mortality due to multiple injuries/ infections

Question 23

What do nocicpetors innervate

Answer 23

Peripheral tissues

Question 24

WHat are the 2 different types of nociceptor fibres

Answer 24

A delta and C fibres

Question 25

What are A delta fibres

Answer 25

Mechanical/ thermal nociceptors that are THINLY myelinated. They mediate first pain
They respond to noxious mechanical and thermal stimuli

Question 26

What are C fibres

Answer 26

Nociceptors that are unmyelinated
They respond to all noxious stimuli
Mediate second pain

Question 27

Gibe examples of the sensation of first pain

Answer 27

Lancinating
Stabbing
Pricking sensations

Question 28

Give examples of the sensation of second pain

Answer 28

Burning
Throbbing
Cramping
Aching sensations

Question 29

How do chemical stimuli activate the peripheral terminal

Answer 29

H+ activates acid sensing ion channels, ATP activates P2X and P2Y receptor, bradykinin activates B2 receptors

Question 30

How do thermal stimuli activate the peripheral terminal

Answer 30

members of the transient receptor potential (TRP) family particulalry TRPV1 activated by noxious heat. TRPV1 is greatly sensitised in inflammation to become active at body temperature

Question 31

What does a stimulus do to ion channels in a nerve terminal and what does this do

Answer 31

Opens the ion channels to elicit a depolarising receptor potential

Question 32

Describe the amplitude of the generator potential

Answer 32

It is grades and proportional to stimulus intensity

Question 33

What does the local current flow trigger?

Answer 33

All or none action potentials at a frequency proportional to the amplitude of the receptor potential
I.e. the greater the depolarisation or the receptor potential, the greater the action potential frequency

Question 34

Where are the nociceptor neurones most sensitive

Answer 34

At the lower end of the stimulous strength

Question 35

What is the unusual property of peptidergic polymodla nociceptors

Answer 35

They have both afferent and efferent functions

Question 36

What are the afferent functions

Answer 36

Transmit nociceptive information to the CNS via release of glutamate and peptides within the dorsal horn

Question 37

What are the efferent function

Answer 37

They release pro-inflammatory mediators (e.g. calcitonin gene related peptide, substance P) frmo peripheral terminals - contributes to neurogenic inflammation

Question 38

What does the noxious stimulation in the long term do?

Answer 38

Increases spinal excitability contributing to hyperalgesia and allodynia

Question 39

Why are C fibres described as being peptigerdic

Answer 39

They utilise peptides as their neurotransmitter at the central termius