Physiology of PAIN

Question 1

Outline the trigeminal pathway of pain ?

Answer 1

1) C fibres

2) trigeminal nerve –> Brain to cortex

Question 2

Pain phenomena
what is it ? why does it occur ?
(2)

Answer 2

Refered pain and neuropathic pain
( originated in one part and percieved from elsewhere)
ie:
- pain from heart , is referred to left arm ( same region of brain processes this , that’s why we mix up signals )

Question 3

outline the pain pathway

5

Answer 3

1) stimulus activates a receptor, A delta or C fibres activated
2) glutamate and substance P are releases in between 1/2 order neurones , 2nd order crosses over
3) 2nd order neurone ascends in spinothalamic tract to thalamus
4) A delta fibres release Glutamate in thalamus
5) AP–>Somatosensory cortex

Question 4

outline the gracile fasciculus pathway

sensory information from the lower half of the body entering the spinal cord at the lumbar level

Answer 4

1) Dorsal horn synapses, doesn’t cross over
2) STAYS on same side
3) crosses over in the medulla

Question 5

what is acute pain ?

Answer 5

1) Acute is due to accidents = nociceptive and inflammatory , sudden onset in response to a discrete event
2) recedes during healing

Question 6

What is chronic pain ?

4

Answer 6

1) neurological pain = LESION, or disease
2) Persists long after recovery , more than 3 months
3)often hard to tie to one event
4)Unresponsive to analgesics
( MS, spinal chord injury , diabetic nephropathy)

Question 7

what kinds of neuropathic pain are there ?(3)

- what can they be due to

Answer 7

1) Hyperalgesia = increased intensity of pain sensation
2) Allodynia = sensation of pain in response to something that wouldn’t cause pain
3) Phantom lymb pain ( limb has been amputated, but they can still feel pain from that limb)

DUE TO :

• increases PGE
• increases Na+ channel expression (cell is more positive , so threshold potential is more likely to be reached)
• increased glutamate release / receptors from 2nd order neurone
• new A - beta fibres expression , and pathways to cause pain sensation from feathers etc

Question 8

Describe the descending pathway and explain how its activation causes analgesia.

Answer 8

• Serotonin release causes GABA to be released
• GABA activates CL- channels. on the dorsal horn neurone
• this means Cl- moves into the cell causing hyperpolarisation
• This means less action potentials are fired , hence less pain

Question 9

Identify circumstances when analgesia may be naturally effective.

Answer 9

• Rubbing , hot and cold
  1) ice pack = decreases swelling
  2) Hot = muscle relaxation
  3) Rubbing = increases activation of the Beta mechanoreceptors = inhibits Delta and C fibres of pain

Question 10

Identify four types of pharmacological analgesics and explain how they work.

Answer 10

• NSAIDS
• OPIOIDS
• ANTI-depresssants
• Local anaesthetics ( lidocaine)

Question 11

Describe the enkephalin pathway

Answer 11

1) Serotonin and Noradrenaline is released from descending neurone in the substansia Gelatinosa
2) This causes presynaptic neurone to block Substance P ,
2) ALSO Interneurone is stimulated (( opioid neurone)–> releases enkephalin
- inhibits the pre septic neurone, close the V-G ca2+ channels, less neurotransmitter release (hence less pain)
- activation of mew receptor , opens K+ channels and K+ leaves the cell on the post synaptic neurone = hyperpolarized = less AP = LESS PAIN

Question 12

How do antidepressants work ?

Answer 12

1) Selective Serotonin Re UPTAKE Inhibitors (increase Serotonin levels)
- this means more GABA is activated = more cl- channels open = cell is more hyperpolarized causing less APs
- increase activation of descending analgesic pathway
- hence pain relief