Pain

Question 1

Acute pain is a sensation associated with a noxious stimulus. What are some examples of this stimulus type?

Answer 1

Chemical, thermal, pressure

Question 2

Describe neuropathic pain

Answer 2

Pain not directly linked to a noxious stimuli. It is a neurological disease affecting the perception of pain

Question 3

Name the two types of nociceptors

Answer 3

Slow C fibres

Fast A-delta fibres

Question 4

Describe C nociceptor fibres. Describe the pain experienced

Answer 4

Slow fibres that are innervated in non life or death scenarios.
Fibres do not have a myelin sheath
Pain is more of a dull/aching pain

Question 5

Describe A-delta fibres and the pain they experience

Answer 5

Fast signals carried by myelinated fibres.

Produces sharp pain

Question 6

Describe the ascending pain pathway

Answer 6

Afferent neuron takes signal to spinal cord. It synapses in dorsal horn and causes withdrawal reflex. The pain signal is delivered to the thalamus. It then travels to the somatosensory cortex and the limbic system

Question 7

Describe the descending pain pathway

Answer 7

Brain sends signals to the PAG (periaqueductal grey) region of midbrain. PAG then sends signals to RVM which sends signals to dorsal horn to reduce the sensation of incoming pain. Many neurotransmitters are involved in this pathway (5-HT, GABA, etc)

Question 8

Injury causes cell damage which results in the release of ….

Answer 8

K+ from cells, local bradykinin release and prostaglandin synthesis

Question 9

What effect does K+ and bradykinin release have on the transmission of pain signals

Answer 9

Mediates pain signal transmission down the afferent neuron fibre

Question 10

What affect does release of substance P have?

Answer 10

Stimulates release of 5-HT, histamine and additional bradykinin

Question 11

If the brain has no nociceptors, how are headaches painful?

Answer 11

Pain arises from the nociceptors in the tissue surrounding the brain (e.g. muscles and blood vessels)

Question 12

Describe tension headaches and treatment.

Answer 12

Caused by tension in the muscles

Treated with simple analgesics

Question 13

Describe cluster headaches and their treatment.

Answer 13

Rare form of headache concentrated behind the eye. Can also experience nasal congestion
Treated with triptans or simple analgesics

Question 14

Describe trigeminal neuralgia

Answer 14

Headache due to trigeminal nerve firing. Pain is experienced across the face near the cheeks
Common in elderly

Question 15

Describe the vascular theory of migraines

Answer 15

Intracranial blood vessels constrict, causing the visual aura. This is followed by rebound vasodilation which returns the blood flow to normal. The sudden spike in intracranial pressure causes the headache and other symptoms

Question 16

Describe the neuronal theory of migraines

Answer 16

A wave of depression / neural inhibition spreads across the cortex very quickly, causing the aura. This leads to an ionic imbalance and increased extra cellular concentrations of K+. This heightened concentration leads to reduced blood flow

Question 17

Describe the inflammation theory of migraines

Answer 17

Trigeminal nerve activation (e.g. by excessive clenching of teeth), leads to activation of mid brain and pons where inflammatory neuropeptides are released (e.g. substance P and CGRP). the CGRP causes vasodilation

Question 18

Explain the role of 5-HT in migraines + role of drugs

Answer 18

Variable serotonin transmission is common in migraines. In the beginning of the migraine, 5-HT is released from platelets causing vasoconstriction. This is followed by a sudden, sharp decrease in 5-HT levels leading to sudden vasodilation. The goal of serotonin agonists or antagonists in migraines is to prevent the rapid increase / decrease

Question 19

Explain prophylactic drug treatment of migraines.

Answer 19

Beta blockers - antagonise b2 adrenoreceptors on blood vessels, inhibiting vasodilation that occurs in the second wave of migraine

Anti-epileptic drugs - reduces neuronal nociceptor excitability

Question 20

Triptans work in both 5-HT 1D and 1B receptors. Explain their MOA

Answer 20

1B - causes vasoconstriction, preventing the rapid vasodilation that causes pain

1D - prevents the release of pro-inflammatory neurotransmitters