L14: Pain

Question 1

What are the 3 types of pain?

Answer 1

acute, chronic and intermittent

Question 2

What is the disorder associated with loss of pain sensation?

Answer 2

CIPA

Question 3

What causes CIPA?

Answer 3

mutation in gene for a nerve growth factor so sensory nerves don’t develop properly

Question 4

What are the 3 classes of nociceptor? What are they activated by?

Answer 4

• thermal: activated by v high or low temps
• mechanical: activated by intense pressure
• polymodal: activated by high intensity mechanical, thermal, or chemical stimuli

Question 5

What are C fibres and what signal travels along them?

Answer 5

unmyelinated axons - signal ongoing slow dull pain (polymodal receptors)

Question 6

What are A∂ fibres and what signal travels along them?

Answer 6

thinly myelinated axons - signal acute onset (thermo & mechanoreceptors)

Question 7

What type of receptors are usually featured on nociceptors? What stimuli are they sensitive to?

Answer 7

TRP (Transient Receptor Potential) channels - sensitive to lots of different stimuli

Question 8

Describe the ascending somatosensory pathways for pain

Answer 8

dorsal root → synapse on dorsal horn of spinal cord projection neurons → cross midline → ascend to thalamus (via spinothalamic tract) → thalamic neurons project to somatosensory cortex and other nuclei involved in pain response ⇒ allows us to locate pain

Question 9

What is hyperalgesia? What causes it?

Answer 9

• enhanced pain
• usually due to previous injury
• often due to inflammation and release of chemicals from damage site

Question 10

What is allodynia?

Answer 10

• Pain in response to innocuous sensory stimuli

Question 11

What is substance P? What does it do?

Answer 11

• local transmitter
  
  • activates mast cells to release histamines → inflammation

Question 12

How can hypergesia result in chronic pain?

Answer 12

strength of synapses in CNS changes→ sensitisation of networks in nervous system and brain → chronic pain [very complex]

Question 13

Describe the gate control model, with examples

Answer 13

Pain signalling can be “gated” by stimulation of non-pain sensory fibres from same area which activates inhibitory interneurons in dorsal horn, reducing output of projection neurons = less excitable, less APs
- e.g. rubbing site of injury
- e.g. TENS (provides different signal from area → decreases pain system)

Question 14

Are opioid receptors generally excitatory or inhibitory?

Answer 14

Inhibitory -> activation can lead to analgesic effects

Question 15

How do NSAIDs work?

Answer 15

inhibit cyclooxyrgenase enzymes to reduce prostaglandin synthesis, have pain suppression effects both at site of injury and in sensory neurons in dorsal root ganglion (DRG) and CNS

Question 16

what do prostaglandins do?

Answer 16

• involved in producing inflammation and pain
• bind to lots of different receptors in free nerve ending → e.g. TRP channel family

Question 17

What is referred pain?

Answer 17

poor localisation of pain bc not able to differentiate between skin and viscera

Question 18

What is thought to cause phantom limb sensation/pain?

Answer 18

• amputation may cut peripheral nerve but cell body stays alive in dorsal root ganglia
• still have activation of this nerve, brain interprets that limb is still there