Circadian Rhythm – Part 1 : The Suprachaismatic Nucleus

My dearest Neuro loves,

I will be starting a new series on Circadian Rhythms. I have recently been involved in a number of experiments that were fundamentally involving circadian rhythms. I also had the pleasure of attending a conference in Montreal that featured some of the most prominent circadian researchers; yes I maintained a professional manner, all giggling, blushing and jumping up & down had to be suffered by my friend/mentor Lanie. So this post is for her, she not only put up with mile a minute tangent filled monologues, she endured anxious/stress Rim (she scares me) and is my portal to everything circadian related. 

The term circadian rhythm has been used increasingly within the mainstream media and has always been one of the most fascinating research areas within Neuroscience/Physiology.  The circadian rhythm is organized by an internal clock that has a period of roughly 24hrs.  Although these cycles are endogenously run, they are also governed by external cues (primarily changes in light and dark cycles).  This master clock is located in your brain in an area called the Suprachiasmatic Nucleus  (SCN) where Supra means above and Chiasm is actually the optic chiasm, which is actually the location of this lovely region (how impressed are you with the original names of brain regions?!?!)

Allow me to give you a brief overview of where this regions is, the SCN is actually located at the anterior lower portion of the hypothalamus (the hypothalamus, much like the hippocampus, is one of the BEASTS of brain regions, it controls everything in our body worth controlling… I am a big fan). The SCN is made up of two parallel nuclei that are shaped like little wings. Within these nuclei are thousands of neurons, which are believed to be the cellular clocks that drive the master clock.

Now, we all know that the brain receives information from the eyes via the optic nerves which conduct visual information onward to the thalamus, the visual cortex and so forth. Unlike the rest of the brain, the SCN has a VIP visual channel, streamed via the retinohypothalamic tract. This allows the SCN to receive and process information on the environment, ie, the durations of the light and dark cycles.

So an internal master clock, which is run by your environment, synchronizes the rest of clocks in your body (oh yes, there are more clocks, imagine your body full of little dials and levers. Now you can’t stop, cool eh?). What does that mean with regards to YOU? Why should you care about a clock?

Well, a lot of human behaviour is based on circadian rhythms.  Behaviours such as: locomotor activity, feeding, sleeping and learning and many more. Physiologically, your body also exhibits circadian rhythms, for example your body temperature fluctuates based on your circadian rhythms. The many disorders in which circadian rhythms play a role include: depression, sleep disturbances, metabolic dysfunctions and urinary dysfunctions but these just barely scratch the surface. In essence, you mess up your circadian rhythms (and you can, quite easily actually) you end up messing with your sleep-wake cycles, body temperature, hormonal release and moods.  Just an FYI, mammals are not the only species that exhibit circadian rhythms, these rhythms are present in bacteria, fungi, rodents   (As one of our loyal readers pointed, rodents are mammals..I knew that, I just got overexcited typing;))and fish.

I will be systematically discussing the relationship between circadian rhythms and all of the above.  I think we should look at jet lag next, that would fun!

Stay Nerdfabulous

Rim

Ps.

One of the best Circadian Rhythms website out there;

http://www.circadian.org/biorhyt.html

Check out the tab EMCP, up up on our page, the first powerpoint presentation has some slides covering anatomy so you can see how awesome my descriptions are of where the regions are 😛

A lovely review:

Vitaterna MH, Takahashi JS, Turek FW. (2001). Overview of Circadian Rhythms

Alcohol Res Health, 25 (2), 85-93