You may be a sleepy head, but you've often experienced the "sleep shudders", "sleep jerks," or "hypnic jerks." It's an unpleasant feeling of jerking awake when you dream about falling through the sky.
You're not alone in feeling it, but about 70 per cent of the population feels these jerks. The most common cause of these jerks is that the brain is undergoing a "sleeping-waking war."
The reticular activating system (RAS) function in our brain is responsible for our "sleep-wake cycle" It holds the control system on our alertness. It is warring with the ventrolateral preoptic nucleus (VLPO), which helps us to sleep. This VLPO has also been described as the "sleep switch."
Hence, the VLPO controls our sleep, while the waking part is controlled by the RAS. Hence, while trying to fall asleep, the two control systems are in a duel. Even as our brain becomes sleepy, the "daytime energy" suddenly gets invigorated and erupts into random movements, along with a falling dream.
The sleep jerks could be called "the last gasps of normal daytime motor control."
Writer Tom Stafford explains: "Rather than having a single "sleep-wake" switch in the brain for controlling our sleep (i.e. ON at night, OFF during the day), we have two opposing systems balanced against each other that go through a daily dance, where each has to wrest control from the other."
On the other hand, some scientists who are fond of the theory of evolution believe that the phenomenon is responsible for these jerks, and it is "an ancient primate reflex to the relaxation of muscles during the onset of sleep - the brain essentially misinterprets the relaxation as a sign that the sleeping primate is falling out of a tree, and causes the muscles to quickly react."
Would such a theory hold water today? Evolution has already got us into a state in which we neither climb too many trees, and even if we did, we are not likely to fall asleep on them.
Still, more research is needed to arrive at a conclusion. Let the VLPO and RAS slug it out unless you want them to smoke the peace pipe.
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