Above: Image © PeopleImages, iStockphoto.com

The next time you're watching Meredith Grey or Derek Shepherd work their magic (or at least hope for a medical miracle) on Grey's Anatomy, think back to your own visits to a doctor's office or hospital. Did you ever get a needle that made you say "Ouch!" or have a broken limb casted after hours of intense throbbing pain?

Experiencing cuts, burns or fractures can be painful. But have you ever stopped to think why we feel that thing called pain in the first place?

Pain-sensing receptors

The whole process, from a painful insult such as touching a hot stove to belting out your favourite curse, starts with nociceptors — receptors in nerve cell endings that sense potential pain.

The cell body of a nerve cell (also called a neuron) that senses pain has two arms. One is equipped with nociceptors and goes to your body's periphery; it's embedded in your skin and internal organs, where it monitors potentially painful stimuli. The other arm reaches into your spinal cord and transmits messages to your brain.

Did You Know?
Your spinal cord, along with your brain, make up your central nervous system or CNS.

Nociceptors are specialized to respond to one of three types of harmful stimuli — heat, pressure or chemicals. After you touch a hot stove, for example, a thermal-sensing nociceptor in your fingertips will fire a chemical message along the neuron's length.

The neuron's transmitting arm then releases special molecules called neurotransmitters to a nerve cell in the spinal cord. This spinal cord neuron is then activated and prompted to signal the alarm and alert the brain.

Pain-fighting drugs

Some kinds of pain are really persistent. In these cases, doctors need to recruit the help of drugs called analgesics. Some analgesic drugs, like AspirinTM and TylenolTM, act where the pain originates, that is on the nociceptors in your skin or internal organs, by reducing sensitivity of these structures to the harmful stimuli.

Did You Know?
Capsaicin, the spicy part of chilli peppers, is used in a topical cream for special kinds of pain.

But other more powerful drugs, opioids, such as codeine or morphine, act on specialized opioid receptors to influence pain. They prevent the release of pain transmitters in the spinal cord and thus block the ability of nerve cells to pass messages along to the brain.

Sounds like drugs offer a neat and tidy solution to the problem of pain, right? So why then do people still experience it? So far, the actions of pain-killing drugs haven't been perfect. Many have unacceptable side effects, like addiction or action on other organs in the body instead of a targeted area.

But the good news is that right now pain research is an exciting and active field of medical science. There are lots of new drugs in development and lots of dedicated scientists identifying potential new therapies. If you want to know what it's like to be a pain scientist, read on!

Researching Pain

Dr. Catherine Cahill, a pharmacologist at Queen's University in Kingston,Ontario, studies the kind of pain that really worries doctors and patients — neuropathic pain. Unlike nociceptive pain, which is usually temporary and caused by damage to body tissues, neuropathic pain is caused by serious injury to the nervous system itself, including nerve cells, the spinal cord and the brain.

Did You Know?
Neuropathic pain can develop from diseases like diabetes or multiple sclerosis, or from events like stroke.

The troubling thing is, once you've got it, it's hard to beat. "Neuropathic pain states are typically chronic, because the nervous system fundamentally changes," says Cahill. "And these states are difficult to treat because we have very limited analgesics available for treating moderate to severe pain."

Opioid drugs, the big guns in the arsenal against pain, are the main class of drugs used to treat severe pain, but even their effectiveness is limited where neuropathic pain is concerned.

Did You Know?
Opioids like codeine and morphine are both derived from the opium poppy.

Cahill says it's because the biological events that create neuropathic pain naturally change the physical structure of nerve cell receptors, as well as their ability to respond to opioid drugs. "Neuropathic pain creates an opioid-tolerant state," she says. "So much of my work is trying to understand the functional changes in opioid receptor signalling that make opioids less effective in treating neuropathic pain."

So the next time you watch a patient in pain on Grey's Anatomy, wailing their way into Seattle Grace Hospital, you'll now know a thing or two about why it hurts so bad.

Learn More!

Merck on Pain

MayoClinic: How you feel pain

Grey's Anatomy

Pharmaceutical Institute: Nociceptive Pain

Pain Terminology

Dr. Catherine Cahill's Research

Photo credit: ABC.com

Asha is a science writer and editor based in Ottawa, Ontario. She is a graduate of Queen’s University, where she received a BSc (honours) in biology, and Concordia University in Montreal, where she studied journalism.

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