While many people are indeed familiar with some of the terminology of sleep science, like ‘melatonin’ or ‘biological clock,’ not everyone fully understands what these mean.
Even worse, when one does become knowledgeable in these processes, it is difficult to apply the knowledge to a healthier lifestyle.
Circadian Cycles:
Circadian rhythms describe many functions in the body and brain following a rhythmic pattern in roughly a 24-hour cycle. Sleep is an example of one of these rhythms along with body temperature, and oscillations in neurotransmitters, some hormonal. Examples include the release of cortisol, human growth hormone, and norepinephrine (but there are many more).
Cortisol, which plays a role in alertness, is fairly active throughout the day and begins to decline as we approach bedtime. Once asleep, cortisol levels gradually rise to prepare for wakefulness and a more active state.
Human growth hormone levels are fairly low throughout the day and peak during the first few hours of sleep. Meanwhile, norepinephrine oscillates throughout the night and is especially active during REM (rapid eye movement) sleep. Together, the oscillations in each of these circadian cycles synchronize to regulate physiology (like sleep and hunger).
Perhaps one of the clearest examples of circadian rhythms in action is the relationship between heart rate, body temperature, and feeling sleepy. Body temperature changes throughout a 24-hour cycle also reflect changes in sleepiness as well as heart rate, and vice-versa. Body temperature increases during the last hour or so of sleep, which helps promote alertness for the day to come. Heart rate also increases. In fact, there is an increased chance of suffering an infarction (heart attack) during early hours due to this transition in heart rate from sleep to wakefulness (1). Increased heart rate means greater circulation and increased alertness.
The Melatonin Factor:
Melatonin is a significant link between the biological circadian rhythms and the 24-hour solar day cycle. It is responsible for the sleepy feeling that we experience as the night approaches. Melatonin levels rise in the absence of light stimuli and drop in its presence. As a result, melatonin levels rise at night and drop during daylight hours.
A rise in melatonin levels often occurs around 2 pm to 4 pm in the afternoon (often referred to as siesta or nap time). At the same time, a small drop in body temperature and heart rate are also observable. Why? Remember that the circadian rhythm is a synchronized system, much like an orchestra. The music (the sleep-wake cycle) is dependent on its many musical instruments (physiological/environmental systems) working together (2).
Being tired is often not enough to begin a sleep episode. This is because the concept of “sleepiness” (as induced by melatonin) is a separate pathway. Individuals with insomnia, for example, are often tired and have low energy from the lack of sleep, yet this tiredness is not enough to produce a sleep episode.
The Biological Clock:
The biological clock regulating circadian rhythms is the suprachiasmatic nucleus (SCN)(3). This nucleus (or nuclear density) is the control center for circadian cycles and is self-regulating. The SCN can turn itself on and off in relation to light stimuli from the environment.
This nucleus is in close proximity to the optic chiasm (which processes light information) and the hypothalamus (which works as a control center for many homeostatic functions). Due to its position in the brain, incoming light stimulates the SCN and affects the hypothalamus (also a control center).
The Significance:
While sleep science can be rather dry, it helps shed light on the complexity of wellness. Health isn’t defined by a single factor like diet, sleep or exercise alone. Rather, these play a role in an even bigger scheme that comes together to define wellness.
Disrupt one factor of wellness, like sleep, and other systems will be affected. For this reason, it is important to have professional guidance when planning to undergo a lifestyle change that could have potentially adverse effects on other aspects of health. Dieting, for example, can be very disruptive when not properly planned but also has the potential to be therapeutic.
Visit CORE today to receive counseling for nutrition, exercise, or general wellness! A stimulating session of personal training can help regulate your sleep schedule. Similarly, a session with our chiropractors of osteopath can help you adjust posture and structural imbalances to help you achieve better sleep quality.
Interested in the science around sleep? Check out Sleep Studies Part 1 and Part 2!
References:
1. Colten, Harvey R., et al. “Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem.” National Academies Press: OpenBook, 4 Apr. 2006, www.nap.edu/catalog/11617/sleep-disorders-and-sleep-deprivation-an-unmet-public-health-problem.
2. “Circadian Rhythms.” UCLAHealth.org, UCLA Sleep Disorders Center, www.uclahealth.org/sleepcenter/circadian-rhythms.
3. White, Leonard E. “Circadian Rhythms – Complex Brain Functions: Sleep, Emotion and Addiction.” Coursera, Duke University, www.coursera.org/learn/medical-neuroscience/lecture/bP3Ex/circadian-rhythms.