MadSci Network: Neuroscience |
Why do you feel two flashes of pain when you touch hot water? Sometimes you leave the water running and then when you put your hands forgetting that it's really hot. You feel the first shock of pain, take your hands out, and then about half a second later feel a longer pain. I think it's probably one of two things. Either the first pain is from the skin and the second is from the more sensitive nerves of your bones warming up or the first is from your spine's automatic reaction and the second is the actual reaction. Konrad, you have essentially answered your own question correctly. Simply put, you are describing the two systems of pain recognition. The first, acute pain, travels down fast myelinated pathways; the second, “chronic” pain, travels on non-myelinated slower neurons, and results in a delayed pain sensation. Pain receptors are sensory nerve endings that are located throughout all organs and tissues of the body, except the brain. These respond to various types of stimulus extremes, such as temperature, cuts, burns or anything that is potentially damaging to the tissue. This may be a bit more detailed than you want, but when an injury, cut or any type of damage occurs, Bradykinin (a pain producing enzyme ) is released from the damaged cells. This bradykinin attaches to the pain receptors (free nerve endings) causing them to transmit pain impulses. These pain impulses travel to the central nervous system through two different fibres: The fibers that transmit impulses quickly are called A- delta fibres. The types of sensations they carry are localized, sharp, pricking, brief sensations. The fibres that transmit impulses more slowly are called C fibres. The types of sensations they carry are dull, burning, aching, longer lasting sensations. This results in the two flashes of pain that you describe. Both of these fibres send impulses by releasing a transmission agent called Substance P. The thalamus, which serves as a switching device, helps to turn on substance P and influence the opening and closing of the pain gate (Substance P is a neuropeptide, but “P” actually stands for "preparation.") Painful impulses from the pain receptors only reach the brain if the "gate" is open. I hope this answers your very interesting question.
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