Pain

Question 1

What is allodynia?

Answer 1

• Neurons become sensitve to non-nociceptive inputs

- Painful response to normally innocuous (non-painful) stimuli

Question 2

What is referred pain thought to reflect?

Answer 2

Convergence of visceral afferent neurons onto similar pathways as the skin afferents in the CNS

Question 3

What is hyperpathia?

Answer 3

• Fibre or axonal loss
• Raises the detection threshold
• Need greater stimulus before pain is detected

BUT when threshold reached - explosive pain

Question 4

Evidence AGAINST the specificity theory?

Answer 4

1) Pain perceived not always proportional to intensity of stimulus
2) Modulation by other stimuli (eg. acupuncture)
3) Perception if pain in severed limbs
4) Referal of pain from viscera –> skin
5) Placebo effect

Question 5

What can cause central sensitistion?

Answer 5

• Local release of prostaglandins from nociceptive dorsal horn neurons causing hyperalgesia
• Damage to central pathways (diabetes, shingles, MS, stroke)

Question 6

What does bradykinin do?

Answer 6

Lowers the threshold of nociceptive molecular fibres (TRPV1)

Question 7

What does the placebo effect prove?

Answer 7

That voluntary or involuntary mechanisms can overcome severe pain

(soldiers can have severe wounds with no pain)

Question 8

What is another name for the spinothalamic tract?

Answer 8

The anterolateral system

Question 9

How does stimulation of the periaqueductal grey (in the midbrain) provide pain relief?

Answer 9

• Activates brainstem nuclei (raphe) which modulates the activity of the dorsal horn neurons
• Dorsal horn decending inputs activate enkephalin-releasing interneurons
• Inhibits C fibres

Question 10

What does capsican do and what does this show?

Answer 10

• Mimics endogenous vanilloids released from stressed cells

- Nociceptors may also detect release of chemicals from stressed cells

Question 11

Where does the affective-motivational pathway input to?

Answer 11

• Limbic system (emotional)

- Hypothalamus (homeostasis)

Question 12

What do prostaglandins do?

Answer 12

• Lower the action potential threshold for pain

- Some painkillers act on the COX enzyme involved in prostaglandin synthesis

Question 13

Which fibres are nociceptive?

Answer 13

Aδ and C

Question 14

What is fast pain?

Which fibres?

Answer 14

• The first pain felt
• Sharp, immediate
• Mimicked by direct stimulation of Aδ nociceptive fibres

Question 15

What causes hyperalgesia?

Answer 15

Release of inflammatory substances bradykinin and prostaglanids when tissue is damaged

Question 16

What other areas of the brain are activated in response to pain?

Answer 16

• Insula

- Cingulate cortex

Question 17

What does the parabrachial nucleus respond to?

Answer 17

• Painful stimuli ANYWHERE on the surface of the body

- In the affective-motivational tract

Question 18

What does measurements in the activity of the somatosensory cortex indicate?

Answer 18

• Somatosensory cortex responds to painful stimuli and intensity of painful stimuli (in the same place as non-painful stimuli in the same location)
• Pain is spatially mapped
• Spinothalamic tract projections preserve topography

Question 19

How prove cellular receptors are specific to pain?

Answer 19

1) Non-nociceptive fibres are already saturated before pain is perceived
Nociceptive fibres fire when pain is percieved

2) If block C fibres, only immediate pain felt
- If block Aδ fibres, only slow pain is felt
- If stimulare Aα or Aβ fibres (non-nociceptive) no pain is felt

Question 20

How does rubbing an area relieve pain?

Answer 20

• Relay of nociceptive signals by the projection neuron is gated by the activity of an inhibitory interneuron
• C fibres usually inhibit the interneuron but Aβ activate it
• Mechanoreceptors Aβ locally inhibit nociceptive C inputs to the spinal chord

Question 21

What is the specificity theory of pain?

Answer 21

• Pain is a DISTINCT sensation

- Detected and transmitted by specific receptors and pathways to distinct pain areas of the brain

Question 22

What is slow pain?

Which fibres?

Answer 22

• The second pain felt
• Delayed but longer lasting
• Diffuse
• Mimicked by direct stimulation of C nociceptive fibres

Question 23

What are the 2 components of the central pain pathways?

Answer 23

1) Sensory discrimitive
- Signals location, intensity and type of stimulus
- Through the spinothalamic tract

2) Affective-motivational
- Signals ‘unpleasantness’ of pain

Question 24

What is pain?

Answer 24

• An enigmatic sensation
• Graded motivation
• Discrimitive sensation (different to different people)
• Can be intolerable

Question 25

What is 'referred pain'?

Answer 25

Pain due to damage of internal organs perceived as coming from locations on the skin

Question 26

How prove molecular receptors are specific to pain?

Answer 26

- TRPV1 (capsican receptor) in Aδ and C fibres is activated by capsican in chillies and by temperatures of 45 degrees - Other TRV receptors are only activated in Aδ alone at higher temps (52 degrees) - Different fibres allow sensation of a more intense pain

Question 27

Evidence FOR the specificity theory?

Answer 27

1) Receptors (cellular and molecular) respond SPECIFICALLY to pain 2) Specific pathways that convey pain 3) Regions of the CNS are specifically and distinctly activated in response to pain

Question 28

What are the mystifying symptoms of pain?

Answer 28

- Emotional variability (what people think pain in) - Radiation over wide regions - Referral (from deep tissue --> skin) - Persistent after sensations

Question 29

What is the convergence theory of pain?

Answer 29

- Pain is a integrated, plastic state | - Pain is a CONVERGENT somatosenssory activity within a distributed network of neuormatrix (neurons)

Question 30

What is hyperalgesia?

Answer 30

- An increased repsonse to a painful stimuli which is normally tolerable - As a result of lowered nociceptor theresholds

Question 31

Describe the affective-motivational pathway

Answer 31

- Shares some paths with the spinothalamic tract but branches off differently - Little/ no topographic mapping (parabrachial nucleus)

Question 32

What does phantom limb pain suggest?

Answer 32

- Pain may be centrally represented - In part may be a central representation of what we expect pain to be - Central maps may partly be preformed (children born without limbs can suffer)