Have you ever noticed that there are certain parts of the day where you are feeling extremely alert, and then there are other parts of the day where you can barely keep your eyes open? This is because of two body systems: sleep/wake homeostasis and your circadian rhythm. The circadian rhythm serves as your internal body clock and tells your body when it is night and day. These two systems can control your sleep drive, or your body's need to sleep at any given time. Continue reading to learn more about your sleep drive and how it interacts with your body clock so that way you know how to better manage your sleepiness.
Sleep slash wake homeostasis and sleep drive
Homeostasis describes the state of equilibrium between two different elements of an organism or group. Sleep/awake homeostasis can balance the need for sleep, which is called the sleep drive, with our need for wakefulness. When we've been away for long periods of time, the sleep doctor tells us that it's time to go to sleep. The longer we are awake, the more pressure that builds up in the sleep drive. As we sleep, we start to regain homeostasis, which encourages wakefulness. This is why in the morning, if you've had a good night's rest, you wake up on your own. Your sleep drive has run out, and your body is telling you that it's time to wake up.
And sleep/wake homeostasis alone was a regulated the sleep drive, we'd probably find ourselves yo-yoing all day. We'd also most likely feel alert in the morning with that alertness wearing off the longer we are awake. However we can feel just as alert at 4:00 PM as we do at 10:00 AM. This is because the homeostasis isn't the only thing that works to regulate our sleep schedules. The circadian rhythm also plays a role.
Sleep drive and circadian rhythm
The circadian rhythm approximates homeostasis and coordination with environmental cues, like light. Because of our circadian rhythm the alertness level can dip and rise throughout the day. This impacts the amount of sleepiness and wakefulness that we can experience during the day.
For example, people feel more tired after midnight and the afternoon slump that can occur right after lunchtime. This means that even if you eat a big lunch or not a big lunch, you could still feel extremely tired in the middle of your day. Then, after a couple of hours, late into the afternoon you can feel more alerts. In addition to these environmental cues, sleep wake homeostasis can impact how tired or alert that we feel. You're more likely to feel tired when you're sleep deprived, unless when you've had sufficient sleep.
The main driver of the circadian rhythm is light. Most people's internal body clock can follow the rise and set of the sun. Exposure to artificial light, therefore, can mess up the circadian rhythm and have the body thinking its light time when it's actually night time. Therefore, this can also impact the sleep drive, even if it happens late at night After you've been awake for a long period of time.
What controls the circadian rhythm?
So how does the body know what time of day it is? The circadian biological clock is controlled by the part of the brain that is called the suprachiasmatic nucleus. This is a group of cells in the hypothalamus that responds to light and dark signals. Whenever light hits the retina, a group cells on the back of the eye, our retina sends signals to the suprachiasmatic nucleus. The retina sets off a chain reaction of hormone production and suppression that can affect body temperature, appetite, sleep drive, and more. The main hormone that is produced is melatonin. Melatonin is the hormone that is responsible for helping our bodies go to sleep period it is produced mostly in the evening and and diminishes the closer we get to morning time.
As soon as the suprachiasmatic nucleus receives light, it stops the production of melatonin. This is why exposing your eyes to blue light from screens, televisions and computers, can mess up their production of melatonin and make it a little bit more difficult for you to go to sleep late tonight.
How sleep drive changes with age
For most individuals, circadian rhythm changes at three key points in our life, infancy, adolescence, and old age. When babies are born, they don't have a circadian rhythm. Therefore the newborn baby sleep cycle is up to like 18 hours a day. It is broken up into multiple short periods because they must wake up to eat, get change, and just experience daytime. As babies age, they develop a circadian rhythm around four to six months of age, which is when they start to sleep for longer periods of time.
Another major change happens around adolescence as up to 16% of teenagers could experience a sleep phase delay. This is when they go to sleep later and wake up later in the morning. It makes no difference what time you send your teenager to bed whenever they're experiencing a phase delay because their bodies just naturally do not want to go to sleep at that time. Due to this shift, melatonin levels don't begin rising until later in the evening and stay elevated later in the morning. This causes them to naturally feel more alert at night and struggle to get up in the morning when it's time to go to school. This is why majority of teenagers struggle with getting sleep, in addition to other factors like cell phones in the room, stress, the development of mental health disorders, etcetera.
The sleep drive changes once more in old age. This is because the internal sleep clock begins to lose its consistency. One reason for this is that the eye is less able to take in the same amount of light. This means that the signal to the suprachiasmatic nucleus is not as strong as it was in our younger years. Older adults tend to become tired earlier in the evening, and awake very early in the morning without the ability to go back to sleep. Seniors experiencing Alzheimer's, dementia, and other neurocognitive diseases can experience even more changes on their sleep drive.
Consequences of a broken sleep drive
Whenever your sleep drive is off, you may feel tired during the day and wired at night. Insomnia and daytime sleepiness are two consequences that could occur due to this. This can happen during times when you experience a change in the way light hits your eye. Daylight savings time and jet lag are two examples of this. When you travel to a new time zone the time and light cues are off from what you're normally used to. Therefore this forces your body and brain to adjust. As your sleep drive adapts to the new circadian disruption, you could feel extremely tired, and have trouble focusing.
Another group that experiences difficulty with their sleep drive is the group of people who have shift work disorder. Shift work disorder can cause insomnia, excessive daytime sleepiness, mood problems, and an increased risk of on the job injuries because of a lack of sleep. These individuals can also have hormonal imbalances of cortisol, testosterone, melatonin levels because they have trained their bodies to sleep opposite of what is natural to them.
If you're an early bird who wants to sleep in, or a night owl who wants to wake up early, changing your circadian rhythm can actually be pretty difficult. It is mostly influenced by genetics, and is mildly influenced by environments. However, you can adjust your sleep drive by following regular sleep and wait times, giving yourself more than seven hours to sleep each night. By adjusting your meals and your caffeine intake you can also change your sleep patterns. Night shift workers can consider bright light therapy to help adjust to their change in light exposure. If you make some lifestyle changes to promote a healthy sleep schedule and sleep issues persist, then it may be time for you to see a sleep health specialist.
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https://www.sleepfoundation.org/circadian-rhythm/sleep-drive-and-your-body-clock