Is there a time of day when you’re more awake and another moment when you’re more tired? Both your sleep/wake homeostatic system and your circadian rhythm, or internal body clock, play a role in determining your sleep and wake habits. Your body’s requirement for sleep is determined by these systems at any given time.
Sleep/Wake Homeostasis and Sleep Drive
“Homeostasis describes a state of equilibrium between the various components of an organism or group.. Homeostasis for sleep/wake balances our desire for sleep, known as a “sleep drive” or “sleep pressure,” with our desire for wakefulness. Sleep drive notifies us when we’ve been awake for too long that it’s time to sleep. Our sleep drive reduces when we return to a state of balance. Finally, when our desire for alertness increases, we realize it’s time to get up and get moving.
If our sleep drive were solely controlled by sleep/wake homeostasis, we’d be swung back and forth between sleep and alertness all day long. Our alertness would peak in the morning and gradually wane as the hours of sleep we received increased. Instead, even if we’ve been awake for hours, we can still feel just as alert at 4:00 p.m. as we did at 10:00 a.m. That’s because our circadian rhythm also plays a part in regulating our sleep schedule, in addition to sleep/wake equilibrium.
Sleep Drive and Circadian Rhythm
When we are exposed to sunlight, our circadian rhythm mimics a state of homeostasis. Our alertness level fluctuates throughout the day as a result of our circadian rhythm, which affects the amount of sleepiness and wakefulness we feel.
During the so-called “afternoon slump,” which can occur after lunchtime, people are most exhausted. Of course, our level of alertness and fatigue is influenced by our sleep/wake homeostasis. When we’re sleep-deprived, we feel more tired than when we’ve had a good night’s sleep.
Circadian rhythms are heavily influenced by light, and the sun’s movements are roughly tracked by the internal clocks of the majority of the population. As a result, exposure to artificial light at night can disrupt our circadian rhythm and, consequently, our desire to sleep.
What Controls Our Circadian Rhythm?
What mechanism does our biological clock use to determine the time of day? SCN cells in the hypothalamus regulate our circadian biological clock by responding to light and dark cues from our environment. The SCN controls the circadian biological clock. The SCN receives a signal from our retinas when we see light. The SCN initiates a cascade of hormone production and repression that has an impact on a variety of physiological functions, including body temperature, appetite, and the desire to sleep.
Cortisol is released in the morning when our body temperature rises and we begin to wake up as the sun comes out. Melatonin levels rise and body temperatures drop as the day turns to night in the evening. The sleep-inducing hormone melatonin remains increased throughout the night. When our eyes detect light, the SCN responds by inhibiting melatonin production, which keeps us awake. This explains why blue-light emitting electronic devices, such as a computer or television, make it difficult to fall asleep at night when exposed in the evening.
Does Sleep Drive Change as We Age?
During birth, adolescence, and old life, the circadian rhythm of most people undergoes significant shifts.
Babies’ circadian rhythms are still developing when they are born. Up to 18 hours of uninterrupted sleep are required by a newborn baby’s sleep cycle. Four to six months into a baby’s life, he or she begins to sleep for longer periods of time.
Up to 16% of teenagers have a sleep phase delay during adolescence. Their melatonin levels don’t begin to climb until later in the evening because of this circadian shift. It’s harder for them to go to sleep before 11 p.m. because they feel more alert at night. The earlier school starts, the more difficult it is for teenagers to achieve the recommended 8 to 9 hours of sleep each night. Many teens find it difficult to concentrate in school when they are sleep-deprived.
In our late twenties and thirties, we begin to lose our desire to sleep. The internal sleep clock becomes less reliable as we get older. Sleep deprivation and cognitive decline are both exacerbated in older adults because they become tired earlier in the evening and wake up earlier in the morning. Alzheimer’s, dementia, and other neurological illnesses diminish an elderly person’s ability to fall asleep naturally.
What Happens if Your Sleep Drive Is Off?
You may feel drowsy during the day and energized at night if your sleep drive is disrupted. Daylight Saving Time and jet lag can cause insomnia and daytime sleepiness because of changes in daylight exposure. As soon as you arrive in a new time zone, your body and brain are forced to adapt to the new time and light cues. It is possible that your circadian rhythm will be disrupted and that you will feel fatigued or ill and have trouble concentrating.
If you work unusual hours or midnight shifts, your circadian rhythm may be disrupted.
Insomnia, excessive daytime sleepiness, mood disorders, and an elevated risk of work-related injuries and accidents can all be symptoms of shift work disorder. Cortisol, testosterone, and melatonin levels may be out of whack in shift workers, which can lead to a host of other hormonal issues.
Circadian rhythms are hard to alter. It is possible, however, to alter your sleep drive by maintaining regular sleep and waking time schedule, allowing yourself at least 7 hours of sleep each night, and altering your meal timings and coffee intake. Bright light treatment is an option for those who work the night shift. Changes in your daily routine that are intended to help you sleep better but are not successful should be discussed with your doctor.