Have you ever noticed how your energy levels ebb and flow throughout the day, seemingly on cue? That’s your circadian rhythm: the internal clock that guides your body through its daily routine, right down to the activity of your cells. But how does this rhythm work, and what pathways are involved? Let’s meet some of the key players that contribute to our circadian rhythms:
The Suprachiasmatic Nucleus (SCN)
The SCN is situated within the hypothalamus, and functions as the central pacemaker orchestrating the body’s circadian rhythm. It senses external cues, particularly light received through the eyes, and acts as the regulatory hub for the internal clock. When the day begins, the SCN initiates a cascade of hormonal releases, such as cortisol, facilitating the promotion of wakefulness. Essentially, the SCN helps adjust our bodily functions to occur at optimal times relative to our environment and activity’s. It’s crucial to note that these rhythms are endogenously generated, meaning they will persist even without external cues like light. The body’s internal clock, governed by the interaction of clock genes and proteins, will continue to regulate essential physiological.
Image made with Biorender.
Eyes and Light
The eyes aren’t just for seeing; they’re also crucial in setting the internal clock. Melanopsin-containing retinal ganglion cells (mRGCs) in the eyes detect light and send signals to the SCN. That’s why exposure to light, especially in the morning, helps synchronize the body’s rhythm with the natural day-night cycle.
The Molecular Level
Inside the cells, a group of genes known as clock genes are the molecular heartbeat of the body’s rhythm. During the day, the production of certain proteins rises and falls in a continuous cycle, this is driven by the clock genes, and dictates the timing of critical processes, from hormone release to metabolism. These protein fluctuations ensure that the body’s activities, from sleep-wake cycles to metabolic peaks and troughs, occur at the right time. Aligning mealtimes with the body’s natural rhythms means that food consumed during the day can be metabolized efficiently, providing energy when it’s most needed, rather than consuming larger meals at night when the body’s metabolic processes may be slowing down in preparation for rest.
Peripheral Clocks
Besides the master conductor in the brain, other organs and tissues also have their own local clocks. These peripheral clocks follow the same beat as the SCN, making sure each organ is performing at its peak during the right part of the day. It’s similar to having a master conductor and a section conductor in an orchestra to keep the rhythm in sync.
(Pivovarova‐Ramich, 2023)
Rhythm Disrupted
Sometimes, our modern lives can throw this finely tuned system out of whack. Irregular sleep schedules, shift work, or jet lag can jumble the rhythm, leaving us feeling out of sync. This disruption can affect sleep, mood, and even digestion. Keeping our internal clocks in tune could be very important for better sleep, improved mood, and overall well-being.
Written by Katie Goddard
References:
Pivovarova‐Ramich O, Zimmermann HG, Paul F. Multiple sclerosis and circadian rhythms: Can diet act as a treatment? Acta Physiologica. 2023;237(4). doi:10.1111/apha.13939
De Somma E, Jain RW, Poon KWC, Tresidder KA, Segal JP, Ghasemlou N. Chronobiological regulation of psychosocial and physiological outcomes in multiple sclerosis. Neuroscience & Biobehavioral Reviews. 2018;88:73-83. doi:10.1016/j.neubiorev.2018.03.011