Anatomy and Physiology of Pain

Question 1

Define transduction

Answer 1

Noxious stimuli translated into electrical activity at sensory nerve endings

Question 2

Define transmission

Answer 2

Propagation of impulses along pain pathways

Question 3

Define perception

Answer 3

Discrimination/affect/motivation

Our interpretation of a stimulus

Question 4

Which primary afferent axon has the widest diameter?
A. A alpha
B. A beta
C. A delta
D. C

Answer 4

A alpha

Question 5

Speed of conduction of stimuli is highest in which primary afferent axon?
A. A alpha
B. A beta
C. A delta
D. C

Answer 5

A alpha

Question 6

What genetic defect/s is associated with loss of transduction/transmission?

Answer 6

Loss of NaV1. 7 (sodium channel subunit)
Results in congenital indifference to pain

trKA - NGF receptor mutation
results in congenital insensitivity to pain with anhydrous CIPA

Question 7

What type of pain is mediated by A delta and some A beta fibres? What is the result of these fibres being activated?

Answer 7

Sharp pricking FAST PAIN
Allows precise localisation of stimulus
Results in reflex withdrawal

Question 8

What type of pain is mediated by C fibres? What is the result of these fibres being activated?

Answer 8

SLOW burning pain
Peptidergic C fibres release peptides peripherally when activated resulting in vasoactive, pro-inflammatory responses

Peptide-poor C fibres have distinct receptors and projections (idk notes say it leads to mechanical nociception?)

Question 9

Which lamina/e is innervated by C fibres?

Answer 9

Lamina I

and interneurones in lamina II (also innervate lamina V through these interneurones)

Question 10

Which lamina/e is innervated by A-delta fibres?

Answer 10

Laminae I and V via projection neurones

Question 11

Which primary afferent axon/s innervate anterior/neospinothalamic tract?*

Answer 11

Mostly A-delta fibres

Come input from C-fibres and A-Beta fibres

Question 12

Which areas of the brain does the anterior/neo spinothalamic tract project to?

Answer 12

1. Ventral posterior lateral and ventral posterior medial thalamus (somatosensory thalamus)
2. Ventral posterior inferior
3. Central lateral nuclei of the thalamus

Question 13

What is the VPL/VPM responsible for, in terms of response to pain?*

Answer 13

Localisation and physical intensity of noxious stimulus

Question 14

Where does the CL nucleus project to in the anterior/neo spinothalamic tract??

Answer 14

ACC (emotion)

PFC + striatum (cognitive function + strategy)

Question 15

Which primary afferent axon/s innervate lateral/paleospinothalamic tract?*

Answer 15

Mainly C fibres

some A delta

Question 16

Which areas of the brain the lateral/paleo spinothalamic tract?

Answer 16

1. Mediodorsal nucleus (ventrocaudal) (MDvc)
2. Posterior nucleus (medial subnucleus)
3. Ventral medial nucleus (posterior)

some projections to VPL, VPM and CL

Question 17

Which areas of the brain does the mediodorsal/ventrocaudal (MDvc) nucleus project to?*

Answer 17

Anterior cingulate cortex

Question 18

Which areas of the brain does the posterior thalamus project to?*

Answer 18

Anterior or rostral insula

Question 19

What are the collateral projections from the lateral spinothalamic tract?*

Answer 19

• Spinal circuitry (reflexes)
• Reticular formation + reticular thalamus (arousal + alerting cortex)
• Periaqueductal grey (descending pain modulation)
• Parabrachial nucleus –> limbic system (memory + autonomic integration)

Question 20

State the 4 cardinal signs of inflammation.

Answer 20

1. Calor (heat)
2. Rubor (redness)
3. Dolor (pain)
4. Tumour (swelling)

Question 21

What causes neurogenic inflammation?

Answer 21

Peptides released from C-fibres

Question 22

Describe how prostaglandins are synthesised.

Answer 22

Phospholipase A2 releases arachidonic acid from cell membranes (due to inflammatory mediators)
Cyclooxygenase 1 and 2 enzymes use arachidonic acid as a substrate for prostaglandin synthesis

Question 23

How do prostaglandins sensitise C-fibres?

Answer 23

By increasing the number of other receptors and increasing the number of OPEN sodium channels

Question 24

How does central sensitisation occur?

Answer 24

nociceptor afferents release glutamate and peptides

this results in increased sensitivity of second order neurones in the dorsal horn

Question 25

Define chronic pain.

Answer 25

Pain or more than 12 weeks, normally associated with an underlying condition

Question 26

What kind of treatment is there for maladaptive pain?

Answer 26

treatments target abnormal neural activity/imbalance in modulatory systems regulating pain
Anticonvulsants and antidepressants can be effective

Question 27

What kind of drugs target pain modulation in peripheral nociceptors?

Answer 27

Local anaesthetics

Anti-inflammatory drugs

Question 28

What kind of drugs target pain modulation in peripheral nerves?

Answer 28

Local anaesthetics

Question 29

What kind of drugs target pain modulation in dorsal horn?

Answer 29

local anaesthetics
opioids
alpha 2 agonists

Question 30

What kind of drugs target pain modulation in cortex?

Answer 30

opioids

alpha 2 agonists

Question 31

Explain how acupuncture is thought the alleviate pain?

Answer 31

Activate A-delta fibres and in doing so stimulates diffuse noxious inhibitory control (DNIC) of pain via the periaqueductal grey

Question 32

Describe the basis of Transcutaneous Electrical Nerve Stimulation (TENS).

Answer 32

Non-noxious afferent are stimulated and this input stimulates lamina II interneurones

Question 33

What part of the brain is sensitive to u opioid antagonists such as naloxone?

Answer 33

ACC-PFC-PAG path

- responsible for the unpleasantness of pain

Question 34

Where does the VPI of the thalamus project to in the anterior/neo spinothalamic tract?

Answer 34

Secondary somatosensory cortex

Question 35

What is/are the function(s) fo the anterior rostral insular?

Answer 35

• emotion
• quality (of pain)
• autonomic integration