better pain control - Toward Better PAIN 60 SCIENTIFIC A...

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Toward Better 60 SCIENTIFIC AMERICAN COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.
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CONTROL Pain comes in a range of unpleasant fl avors. But all pain has one thing in common: those who endure it want it to stop. Yet the most widely used analgesics today are es- sentially folk remedies that have served for centuries: morphine and other opiates derive from the opium poppy, and aspirin comes from willow bark. Although these treatments can give relief, each has its limita- tions. Aspirin and other nonsteroidal anti-infl amma- tory drugs (NSAIDs), such as ibuprofen, cannot ease the most severe types of discomfort. And even opiates, generally the strongest medicines, do not work for ev- eryone. Moreover, they can have serious side effects, and patients tend to become tolerant to them, requir- ing escalating doses to get any relief at all. Over the past 20 years neurobiologists have learned a great deal about the cellular circuits and the specialized molecules that carry pain signals. Today this knowledge is being exploited to devise new strat- egies for managing pain better and causing fewer side effects. Indeed, more approaches than we have room to discuss are now under study. Particles of Fire in the 17th century French philosopher René Descartes enumerated a theory to explain how people sense pain. In his view, a pinch, a whack or a poke es- sentially tugged on a neural rope that then rang a pain alarm bell in the brain. Imagine, for example, burning a foot. “Fast moving particles of fire,” Descartes thought, would create a disturbance that “passes along the nerve fi lament until it reaches the brain.” Descartes was not too far off. Pain generally be- gins at the periphery: in the skin, an internal organ or any other site outside the central nervous system (CNS) that is, outside the brain and spinal cord. Stubbing a toe or leaning against a hot stove activates neurons (nerve cells) called nociceptors that respond specifi cally to hurtful stimuli, such as extreme tem- perature or mechanical pressure, or to chemicals gen- erated in response to injury or infl ammation. Nociceptors have two arms: a sensation-detecting branch that projects out to the periphery, where it in- nervates small patches of tissue, and a second branch that extends into the spinal cord [ see box on page 63 ]. The neuron’s cell body, which resides in a structure outside the spine, sits between the two. When special- ized detector molecules on the peripheral branch en- counter a noxious agent in the skin or an organ, they trigger an impulse that travels up the line, along the central branch and on to an area of the spinal cord known as the dorsal horn. There the nociceptor re- leases signaling molecules called neurotransmitters that activate neurons in the dorsal horn, prompting Advances in understanding the cells and molecules that transmit pain signals are providing new targets for drugs that could relieve various kinds of pain including those poorly controlled by existing therapies Throbbing, itching, aching, stabbing, stinging, pounding, piercing.
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