For each paragraph on an aspect of pain A–E, select the most appropriate option from the following list.
1. Chemical mediators at site of pain.
2. Medium sized myelinated pain afferents.
3. Small unmyelinated pain afferents.
4. Gating of the pain pathway in the spinal
5. Thalamus.
4. cord.
6. Endorphins and enkephalins.
7. Impulse spread to medullary reflex centre.
8. Impulse spread to vagal nuclei.
- . A pin prick to the foot gives rise to a sudden sharp sensation of pain and withdrawal of the affected limb.
- . A relatively crude non-specific sensation of pain is believed to be generated from the site of synapse of fibres in the spino-thalamic tracts.
- Severe pain is usually treated with drugs which act on brain neuronal receptors for endogenous neurotransmitters believed to be released during severe exercise, especially when associated with mortal danger.
- Patients who suffer the severe crushing pain of a myocardial infarction (heart attack) often vomit.
- The pain of muscle and joint damage associated with a sports injury is often treated with drugs which inhibit the formation of prostaglandins.
Medicine
A. Option 2 Medium sized myelinated pain afferents. These are the A fibres which conduct rapidly to give the initial sharp sensation of pain; they also initiate the rapid spinal withdrawal reflex in response to pain.
B. Option 5 Thalamus. This is where the spino-thalamic tracts terminate and synapse. The general unpleasant sensation of pain is generated here, with cortical areas indicating the site of the pain.
C. Option 6 Endorphins and enkephalins. These are the endogenous neurotransmitters on whose receptors the powerful opiate analgesics act to relieve severe pain. Their release during exercise may contribute to the mood-elevating effects of exercise. They may also account for temporary absence of severe pain as a result of injury on the battlefield.
D. Option 7 Impulse spread to medullary reflex centre. The vomiting centre is in the medullar oblongata and can be activated by severe pain from a variety of causes (reflex vomiting).
E. Option 1 Chemical mediators at site of pain. Prostaglandins are believed to be important mediators of persistent pain at a site of injury, particularly involving muscles and joints. Drugs which inhibit prostaglandin formation (NSAIDs: non-steroidal anti-inflammatory drugs) are often effective in this type of pain.
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