THERE IS A CLOCK IN YOUR BRAIN

Have you ever wondered how you sometimes wake up even before the alarm goes off in the morning? Or how you start feeling hungry when the lunch time comes, without even checking the time.
Though you might not be keeping track of the time but your body sure does.There is a clock in your brain.To be fair all the cells of your body has its own clock but the master clock is located inside your brain in a region called Suprachiasmatic Nuclei (SCN).

SCN- Suprachiasmatic nucleus

SON- Supraoptic nucleus

OX- Optic chiasm

SCN regulates the circadian rhythm, which is an endogenous biological rhythm with 24hrs period and is entrainable by environmental cues (eg: light).It will continue even when the environmental cue is not present. Let us take the example of the sleep-wake cycle of human, if we keep a volunteer in a room for a few days without any environmental cues, he/she will start to wake up 1 hr late every day.This happens because human sleep-wake cycle has a period of 25.2hrs (approx.), but the environmental light- dark cycle synchronises it to 24hrs. Hence, without the cue, it starts to show its original periodicity also called free running period.

The light information in case of mammals is perceived by the eyes only. The retinal cells send the message to the SCN through Retinohypothalamic tract (RHT). From SCN it goes to pineal and changes the melatonin profile, melatonin is secreted at night time and is associated with sleep.SCN also synchronises all the clocks present in the body acting as a master clock. Disruption of this clock system may result in different sleep disorders (Eg: Advance sleep phase disorder)

Circadian rhythm is arguably present in every organism of planet earth. So, what is its function? Circadian rhythm allows anticipation of cyclical environmental changes, thus increasing the chance of survival. So a predator knows when to hunt, as it can anticipate when the food availability will be maximum. The circadian oscillator evolved more than 2bya. and plays a major role to increase the fitness. It is present even in cyanobacteria comprising of only three genes. I'll be talking about the details of circadian rhythm in the upcoming blogs, until then keep your neurons firing.