At the 10/3/2007 meeting, we resolved to get a better idea about how certain pain medications work. Here are some links to get us started. Other links are welcome:
These aren’t pain meds, but their mechanism of actions will still be applicable to our conversation:
Selective serotonin reuptake inhibitors (SSRIs)
Amended 10/22/2007 by Friendlich
Pain medications work by blocking an element in the ‘pain chain’. This may be accomplished either directly, as with morphine acting upon the Central Nervous System (CNS), or indirectly by disrupting the operation or production of an associated hormone or enzyme.
Your peripheral nerves extend from your spinal cord to your skin, muscles and internal organs. These peripheral nerve fibers end with receptors that respond to touch, pressure, vibration, cold and warmth, or pain. Nociceptors are responsible for the sensation of pain and are most concentrated in areas prone to injury, such as fingers and toes.
When injured the damaged tissue releases hormones called prostaglandins that cause the tissue to swell. This in turn amplifies electrical signals coming from the nerves. When nociceptors detect a harmful stimulus, such as the hard surface that stubbed your toe, they relay pain messages in the form of electrical impulses along a peripheral nerve to your spinal cord and brain. Severe sensations of pain are transmitted almost instantaneously through an expedited route to the brain.
The nerve fibers that transmit pain enter the spinal cord in an area called the dorsal horn. There, they release neurotransmitters that activate other nerve cells in the spinal cord, which process the information and then transmit it up to the brain.
When news of your stubbed toe travels up the spinal cord, it arrives at the thalamus. The thalamus forwards the message simultaneously to three specialized regions of the brain: the physical sensation region (somatosensory cortex), the emotional feeling region (limbic system) and the thinking region (frontal cortex). Your brain responds to pain by sending messages that moderate the pain in the spinal cord.
One family of common pain relievers known as Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) (i.e. ibuprofen and aspirin) work on a chemical level by inhibiting key enzymes essential to the production of prostaglandins. Specifically, COX-1 is responsible for baseline levels of prostaglandins and COX-2 for the production of prostaglandins through stimulation. When the cells don’t release prostaglandin, pain messages to the brain are slowed and/or lessened. So pain goes away or becomes less severe for as long as the cells aren’t releasing the chemical. (See http://www.elmhurst.edu/~chm/vchembook/555prostagland.html for a detailed molecular explanation.)
Prostaglandins were first discovered and isolated from human semen in the 1930s and, incorrectly believing that they had been synthesized by the prostate gland, were named accordingly. It has since been determined that they exist and are synthesized in virtually every cell of the body. This local production is essential since prostaglandins exert only a paracrine (locally active) or autocrine response before being inactivated and excreted. While one effect of prostaglandin is local inflammation, there are approximately a dozen types of prostaglandin each performing different activities based on the type of tissue affected including smooth muscle contraction, inflammatory mediation, calcium movement, fever regulation, and the aggregation or disaggregation of platelets (blood clotting).
Sources:
1. Mayo Clinic Staff , “How you feel pain.” Mayo Clinic. 13 Feb 2007. Mayo Clinic. 23 Oct 2007, from http://www.mayoclinic.com/health/pain/PN00017.
2. Ophardt, Charles. “Prostaglandins.” Virtual ChemBook. Elmhurst College. 23 Oct 2007, from http://www.elmhurst.edu/~chm/vchembook/555prostagland.html.
3. “Endometriosis and Prostaglandins.” Endo Resolved. 23 Oct 2007, from http://www.endo-resolved.com/prostaglandins.html.
4. Omudhome, Ogbru. “Ibuprofen.” MedicineNet.com. 28 Aug 2007. 23 Oct 2007 http://www.medicinenet.com/ibuprofen/article.htm.
5. Prostaglandin. (2007, October 16). In Wikipedia, The Free Encyclopedia. Retrieved 20:07, October 23, 2007, from http://en.wikipedia.org/w/index.php?title=Prostaglandin&oldid=165025277.
6. Griffin, R. Morgan . “Pain Relief: How NSAIDs Work.” WebMD. 04 Oct 2005. 23 Oct 2007, from http://www.webmd.com/rheumatoid-arthritis/guide/how-anti-inflammatory-drugs-work?page=2.
