Pain physiology

Question 1

What are the three classifications of pain?

Answer 1

Nocioceptive
Inflammatory
Pathological

Question 2

What is the definition of pain?

Answer 2

An unpleasant sensory and emotional experience.

Question 3

What are nocioceptors?

Answer 3

Peripheral primary specific sensory afferent neurones activated by intense noxious stimuli e.g. Chemical, thermal, mechanical etc.

Question 4

Are nocioceptors first or second order neurones?

Answer 4

First order

Question 5

What kind of neurones do nocioceptors relay information to and where are they?

Answer 5

Second order neurones in the CNS

Question 6

Is nocioceptive pain adaptive or maladaptive?

Why?

Answer 6

Adaptive as it is an early warning system that detects and minimises contact with damaging stimuli.

Question 7

Is nocioceptive pain high or low threshold?

Answer 7

High threshold, it is provoked only by intense stimuli.

Question 8

What happens when a nocioceptor is activated by noxious stimuli?

Answer 8

It overrides other CNS activities and initiates a withdrawal reflex. It also initiates an emotional response that allows us to remember this and avoid the stimuli in future.

Question 9

Is inflammatory pain adoptive or maladaptive?

Answer 9

It is adaptive and protective

Question 10

What other two things can inflammatory pain result in?

Answer 10

Pain hypersensitivity and allodynia (innocuous stimuli now elicit pain)

Question 11

What is the benefit of inflammatory pain?

Answer 11

Assists in healing of damages area by: discouraging physical contact and movement.

Question 12

Is inflammatory pain high or low threshold?

Answer 12

Low threshold in order for tenderness to promote healing.

Question 13

What is adaptive pain?

Answer 13

Helpful pain that will encourage behaviour that aids healing.

Question 14

Is pathological pain adaptive or maladaptive?

Answer 14

Maladaptive, it has no protective function

Question 15

What are the two categories of pathological pain?

Answer 15

Neuropathic and dysfunctional.

Question 16

What is neuropathic pain?

Answer 16

Caused by damage or disease affecting the somatosensory nervous system.

Question 17

What two things is pathological pain associated with?

Answer 17

Spontaneous pain and pain hypersensitivity.

Question 18

What is dysfunctional pain?

Answer 18

A pain where there is no obvious neural lesion or inflammatory pain.

Question 19

What causes congenital insensitivity to pain?

Answer 19

Rare condition resulting in loss of function mutations e.g. Missense in gene that encodes Na channels that are highly expressed in nocioceptive neurones

Question 20

What are the symptoms of CIP?

Answer 20

Lip and tongue injury, bruises and cuts, multiple scars, bone fractures, joint deformity and premature mortality.

Question 21

What are the two subtypes of nocioceptor?

Answer 21

A delta (incomplete figure of 8 sign)
C-fibres

Question 22

What type of stimuli do A delta nocioceptors respond to?

Answer 22

Mechanical and thermal stimuli.

Question 23

Are A delta nocioceptors myelinated?

Answer 23

Yes but only thinly

Question 24

What type of pain do A delta nocioceptors mediate?

Answer 24

First or fast pain e.g. Stabbing prickling sensations.

Question 25

Are c fibres myelinated?

Answer 25

No they are unmyelinated so have slower conduction velocity.

Question 26

What type of stimuli do C fibre nocioceptors respond to?

Answer 26

All types of stimuli collectively.

Question 27

What type of pain do C fibres mediate?

Answer 27

Second or slow pain e.g. Burning, throbbing cramping aching sensations.

Question 28

How does a stimulus in sensory neurones illicit an action potential?

Answer 28

They open ion channels in the nerve terminal.

Question 29

What is the potential created by stimuli at a sensory nerve terminal called?

Answer 29

Depolarising receptor or generator potential.

Question 30

What affects the generator potential amplitude?

Answer 30

The intensity of the stimulus, the generators potential is graded to this.

Question 31

What effect does the generator potential amplitude have on the resulting action potential?

Answer 31

Action potential are triggered at a frequency proportional to the amplitude of the receptor potential.

Question 32

Where do nociceptor nerves enter the spinal cord? Where are their cell bodies? What happens to the after they enter the spinal cord?

Answer 32

Enter through the dorsal horn Bodies in the dorsal root ganglion or trigeminal ganglion. They cross over the spinal cord and ascend to brain up the anterior horn.

Question 33

What is a subset of C fibres that have afferent and efferent functions?

Answer 33

Peptidergic polymodal nociceptors.

Question 34

What peptides do afferent peptidergic polymodal nociceptors release in the dorsal horn?

Answer 34

Substance P and neurokinin A

Question 35

What substances do efferent peptidergic polymodal nociceptors release?

Answer 35

Inflammatory mediators e.g. Calcitonin gene-related peptide (CRGP), substance P etc.

Question 36

What can chemical release from efferent peptidergic polymodal nociceptors contribute to?

Answer 36

Neurogenic inflammation.

Question 37

What does release of substance P cause?

Answer 37

Vasodilation and extravasation of plasma proteins Release of histamine from mast cells Sensitises surrounding nociceptors

Question 38

What does CRGP do?

Answer 38

Induces vasodilation

Question 39

What stimuli can trigger release of chemicals from petidergic nociceptor efferents?

Answer 39

Tissue damage or inflammatory mediators.

Question 40

What is the primary transmitter released from the primary afferent in the dorsal horn?

Answer 40

Glutamate

Question 41

What is the name for the area in the dorsal horn where primary afferent axons terminate?

Answer 41

Laminae of rexed

Question 42

Where do nociceptive C and A delta fibres mostly terminate?

Answer 42

Superficially in laminae 1 and 2 (and also 5 for A delta)

Question 43

What do nociceptive specific cells synapse with?

Answer 43

C and Adelta fibres.

Question 44

What type of cells only receive input from Abeta fibres?

Answer 44

Proprioceptive

Question 45

What type of neurones receive input from C fibres Adelta and Abeta fibres?

Answer 45

Wide dynamic range neurones.

Question 46

Where do second order neurones ascend the spinal cord?

Answer 46

In the anterolateral system

Question 47

What does the anterolateral system in the spine mostly consist of?

Answer 47

The spinothalmic tract and the spinoreticular tract.

Question 48

What types of neurones does the spinothalmic tract project? What lamina do they come from? Where does it terminate?

Answer 48

Fast fibre Adelta neurones Lamina 1 Posterior nucleus of the thalamus WDR neurones Lamina 5 Terminates in posterior and ventroposterior nucleus of the thalamus.

Question 49

What does pain proprioception require?

Answer 49

Simultaneous firing of both pathways in the spinothalmic tract

Question 50

What does the spinoreticular tract mostly transmit?

Answer 50

Slow C fibre pain neurones

Question 51

Where does the spinoreticular tract connect to in the brain?

Answer 51

Reticular nuclei in the brain stem (periaqueductal grey - PAG) and parabrachial nucleus (PBN)

Question 52

What responses to pain is the spinoreticular tract involved in?

Answer 52

Autonomic responses e.g. Emotional arousal, fear etc.