A 2001 study, Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor, revealed a specific photoreceptor in the human eye (likely most all mammals). “The results suggest that, in humans, a single photopigment may be primarily responsible for melatonin suppression, and its peak absorbance appears to be distinct from that of rod (black/white/night vision/movement) and cone (red/blue/green) cell photopigments responsible for [our normal color spectrum] vision. The data also suggests that this new photopigment is retinaldehyde based. These findings suggest that there is a novel [type 2] opsin photopigment in the human eye that mediates circadian photoreception”[78] This opsin photoreceptor’s sole purpose is to detect light or not light (dark). It is so sensitive that it even detects light when our translucent eyelids are closed. Now I finally have an answer to why I always wake up at sunrise and have never been able to sleep during the day unless I very effectively protect my closed eyes from any direct or ambient light.HC By now you may realize that you really do have a very accurate and dependable biological clock. You may be wondering how these circadian rhythm controlling ipRGCs connect to your biological clock, and perhaps where your biological clock is located? Well, you don’t really need to memorize this, as there is no test at the end of this section, but for general knowledge here it is: the ipRGCs (melanopsin-containing ganglion cells located in the retina) detect light (or not light) which is then converted into nerve signals and sent along the retinohypothalamic tract (specialized optic nerve) to an area of the brain called the suprachiasmatic nucleus (SCN). The SCN (the biological clock) is pine cone-shaped, about the size of a grain of rice, and is located at the front (anterior) area of the hypothalamus, immediately behind (superior) of the optic chiasm (CHO). OK, that might sound a little bit over-whelming for most everyone but a medical professional, so here’s a diagram to help out the rest of us. The SCN sends information to other hypothalamic nuclei and the pineal gland to modulate circadian rhythmicity, production of hormones such as cortisol and melatonin, sleep, body temperature, physical activity, alertness, immune function, and metabolic/digestive processes. The SCN also controls slave oscillators in the peripheral tissues, which exhibit their own diurnal (24-hour) rhythms, but are kept in synchrony by the SCN.[89] Despite its very tiny size, the SCN is a high density organ composed of about 20,000 neurons. Within each neuron, clock genes and proteins compose interlocked regulatory feedback loops that generate circadian oscillations on the molecular level. SCN neurons dispersed in cell cultures display cell-autonomous oscillations, with periods ranging from… [20-28 hours].”[89] Perhaps the next time you see a grain of rice on your plate, you may think of the suprachiasmatic nucleus (our biological atomic clock) which masterfully synchronizes much of the human body’s daily functions to the rise and fall of the Sun. ©2014
Posted on: Sat, 15 Mar 2014 08:24:19 +0000
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