Pain

Question 1

What is specificity theory?

Answer 1

Pain is a distinct sensation
- Detected and transmitted by specific pathways to distinct “pain areas”

Question 2

What is convergence theory?

Answer 2

Pain is an integrated plastic state
- Represented by a pattern of convergent somatosensory activity within the distributed network

Question 3

What is a nociceptor?

Answer 3

An afferent with a free nerve ending

Question 4

How are nociceptors classified?

Answer 4

According to activating stimulus, fibre type and conduction velocity
- Light myelinated A delta fibres
- Unmyelinated C fibres

Question 5

What are the 2 categories of pain?

Answer 5

Fast
Slow

Question 6

Describe fast pain

Answer 6

• Sharp and immediate
• Can be mimicked by direct stimulation of A delat fibre nociceptors

Question 7

Describe slow pain

Answer 7

Delayed, diffused and long lasting
- Can be mimicked by stimulation of C fibre nociceptors

Question 8

Does stimulation of A delta or A beta fibres elicit pain?

Answer 8

No never
- distinct set of A delta and C fibres (nociceptors) specifically associated with pain detection

Question 9

At what temperature is the capsaicin receptor activated?

Answer 9

45*C

Question 10

What are the 2 components of central pain pathways?

Answer 10

Sensory discriminative
Affective-motivational

Question 11

Describe the sensory discriminate pathway

Answer 11

• Signals location, intensity and type of stimulus

Question 12

Describe the affective motivational

Answer 12

• Signals ‘unpleasantness’ and enables autonomic

Question 13

What tract is involved in the discriminative pathway?

Answer 13

The spinothalamic tract

Question 14

What is the affective-motivational response to pain?

Answer 14

• Shares pathways with the anterolateral system
• Neurons in parabrachial nucleus can respond to painful stimuli from anywhere on the bodies surface
• Strong correlation of pain with cingulate cortex

Question 15

What is hyperalgesia?

Answer 15

Increased response to a painful stimulus
- Hypersensitivity

Question 16

What is Allodynia?

Answer 16

Painful response to a normally innocuous stimulus

Question 17

What are the peripheral effects of the inflammatory response?

Answer 17

• Tissue damage releases a ‘soup’ of inflammatory substances, can affect nerve function, recruit mast cells and neutrophils and increase local blood flow

Question 18

Function of bradykinin?

Answer 18

Directly affects the function of nociceptive molecular receptors
- Such as TRPV1

Question 19

Describe central sensitisation

Answer 19

Sensitisation can result from the activity dependent local release of substance
- Prostaglandins from nociceptive dorsal horn neurons
- Lowers thresholds for ap , gives rise to hyperalgesia
- Results in allodynia

Question 20

Describe hyperpathia

Answer 20

• Variant of hyperalgesia and allodynia
• Fibre/axonal loss/damage results in raising detection threshold
• Explosive pain

Question 21

Describe phantom limb pain

Answer 21

Experienced after amputation
- Central representation of the body is not passive
- Central maps may be partly preformed
- Pain may be a result of what we expect it to be

Question 22

Describe referred pain

Answer 22

• Pain due to damage in the viscera perceived as coming from specific locations in the skin according to the organ affected

Question 23

Describe the central modulation of pain

Answer 23

Mechanisms exist, voluntary or involuntary, to overcome severe pain

Question 24

What is the physiological basis of pain modulation?

Answer 24

Stimulation of periaqueductal grey activates brainstem nuclei
- Modulates activity of dorsal horn neurons
- Descending inputs activate enkephalin which releases interneurons to inhibit nociceptive fibres

Question 25

How does pain relief happen locally?

Answer 25

Local inhibition by mechanoreceptors (A delta) of nociceptive (C fibre) inputs in the spinal cord

Question 26

What did Melzack and Wall propose?

Answer 26

Pain perception is the result of integration of convergent sensory information