Lecture 17

Question 1

How does Pain typically begin?

Answer 1

With an activation of nociceptors

Question 2

What is Pain a product of?

Answer 2

CNS processing a variety of neural signals

Question 3

What is associated with a loss of pain sensation?

Answer 3

Congenital Insensitivity to Pain with Anhidrosis (CIPA)
- Sensory and autonomic neuropathy
- Caused by mutation of a nerve growth factor receptor

Question 4

List the 3 main classes of Pain Signals

Answer 4

1) Mechanical
2) Thermal
3) Chemical

Question 5

What are Mechanical Pain Signals activated by?

Answer 5

Intense mechanical deformation/pressure

Question 6

What are Thermal Pain Signals activated by?

Answer 6

Extremes of temperature
- High: > 45 °C
- Low: <5 °C

Question 7

What are Chemical Pain Signals activated by?

Answer 7

• H+ (acid)
• Histamine
• Cytokines
• Prostaglandins

Question 8

Describe C fibres

Answer 8

• Smallest diameter
• Unmyelinated axons
• Signal ongoing pain
• Dull throbbing (polymodal receptors)

Question 8

What can Pain Signals also be and what are they activated by?

Answer 8

• Polymodal
• Activated by combinations of mechanical, thermal, chemical

Question 9

What 2 fibres are associated with Pain Signals?

Answer 9

1) C fibres
2) Aδ fibres

Question 10

Describe Aδ fibres

Answer 10

• Small diameter
• Thinly myelinated axons
• Signal acute onset of pain
• Sharp pain (thermo & mechanoreceptors)

Question 11

What type of axon does pain transmission occur on?

Answer 11

Afferent axon

Question 12

Where does Pain Transmission synapse and what does it release?

Answer 12

• Synapse in CNS
• Releases glutamate or substance P

Question 13

What is the Gate Control Model?

Answer 13

Pain signalling can be “gated” by stimulation of non-pain sensory fibres from same area

Question 13

What is Hyperalgesia?

Answer 13

• Persistent or enhanced pain sensation
• Often due to inflammation and release of chemicals
  (Prostaglandins and Cytokines)

Question 14

What does the Ascending Somatosensory Pathway carry sensations of?

Answer 14

Pain, temperature and some touch

Question 15

What is Allodynia?

Answer 15

Pain from an innocuous stimuli
- eg feather-light touch causes pain

Question 16

What therapies did the Gate Control Model theory lead to?

Answer 16

• TENS (Trans Epidermal Nerve Stimulation)
• Implantable spinal cord stimulators

Question 17

What can Pain Signalling be modulated by?

Answer 17

Descending pathways from brain
- e.g. Endogenous opiates

Question 18

What tracts are the signals sent via in the Gate Control Model?

Answer 18

Via anterolateral tract to thalamus

Question 19

Which fibre is associated with the GCM?

Answer 19

C fibre

Question 20

What do the C fibres do in the GCM?

Answer 20

Activate projection neurons in spinal cord

Question 21

What does the GCM result in?

Answer 21

Reduction in output of projection neurons

Question 22

What does Prostaglandins binding lead to?

Answer 22

Ion channels opening
- Makes nerve terminal more excitable
- Can also increase growth of nerve endings

Question 23

What do Pain medications inhibit?

Answer 23

Cyclooxygenase enzymes to reduce prostaglandin synthesis

Question 24

What does the inhibition of cyclooxygenase enzymes do?

Answer 24

Pain-suppression effects both at site of injury and in sensory neurons in DRG and CNS

Question 25

What causes referred pain?

Answer 25

Convergence of visceral and somatic afferent neurons onto ascending pathways - Brain cannot distinguish whether the stimulus arose in skin or viscera

Question 26

What afferent's provide information on tooth load?

Answer 26

Periodontal

Question 27

Where do the sensations from the pulp go?

Answer 27

Central pain pathways, so sensation is predominantly pain

Question 28

Where are Nociceptors located?

Answer 28

- Skin - Joints - Muscles - Viscera - NOT in the brain

Question 29

What do Endogenous opiates bind to?

Answer 29

CNS receptors, inhibiting pain

Question 30

What do NSAIDs do?

Answer 30

Inhibit prostaglandin synthesis (via COX enzymes), reducing nerve terminal excitability and inflammation

Question 31

What neurotransmitters are released in the spinal cord during pain transmission?

Answer 31

Glutamate and Substance P

Question 32

Give an example of referred pain relevant to dentistry

Answer 32

Neck or skull pain may be perceived as temporomandibular or tooth pain due to trigeminal nerve convergence

Question 33

What type of fibres innervate the dental pulp?

Answer 33

- Aδ fibres (sharp pain) - C fibres (dull, aching pain)

Question 34

What triggers tooth pulp nerve activation?

Answer 34

Noxious stimuli like heat, cold, pressure, osmotic and chemical irritation (e.g., sugar)

Question 35

What role does inflammation play in tooth pain?

Answer 35

It lowers the activation threshold of nerves, leading to hyperalgesia and allodynia