Question
PASSAGE 1: Melatonin and Sunlight
By Priyanka Walker
When the Sun sets on the horizon, cities around the globe slow down, people begin to yawn, and bedtime ensues. In contrast, when the Sun rises, the world repeatedly wakes. What causes this consistent sleep and wake cycle that coincides with dawn and dusk? Is it simply a universal human habit that most people continue to do because everyone else is doing it? No, it’s not a habit or a tradition handed down from our great-grandparents’ great-grandparents. Like many things, science explains that our tendency to follow this pattern is deeply rooted in both our physiology and our body’s connection to its environment. Our desire to sleep when it’s dark and to rise when it’s light is due to a complex and fascinating phenomenon called the circadian rhythm, a twenty-four-hour cycle connected to our exposure to sunlight as well as the activation of several hormones within us.
To understand circadian rhythm, one has to first understand melatonin, the sleep hormone. Hormones are the chemical messengers our body uses to initiate activity in various anatomical systems. In this case, the hormone melatonin triggers our bodies to transition into sleep mode, and then the hormone continues to be produced for several hours each evening, reminding several of our bodily systems to remain in resting state.
Melatonin is released from tissue all over the body, but the primary producer of this sleepy-time hormone is a part of the brain called the pineal gland. The pineal gland usually starts producing melatonin around 9 p.m. as long as it is uninhibited by human routines such as nightshift schedules, bright light, or travel to different time zones (also known as “jet lag”). Melatonin levels at night in a healthy human are typically ten times what they are during the day. It’s no wonder that it can be extremely difficult to fight off sleep at night—there’s an entire army of hormones at work.
When this blast of nighttime melatonin takes place in the pineal gland, it uses the circulatory system to carry melatonin through the blood to various parts of the body that have melatonin receptors. When these receptors receive melatonin, they respond in a variety of ways. For example, the heart rate slows and the body temperature lowers which both encourage relaxation so that sleep takes place. Eventually, melatonin stops being released (it is typically sometime around 6:30 a.m.), and these same body systems start waking up. Later in the day, the process repeats itself again starting with the melatonin release from the pineal gland.
Clearly, melatonin is tightly linked to our circadian rhythm, but what causes the pineal gland to kick into action and start releasing melatonin? You probably guessed it—it’s the Sun that triggers this entire process. Sunlight hits our eyes, and even more specifically, it hits the retina. It may surprise you to find out that our eyes are actually a part of the brain—a very important part at that! Your retina, the innermost lining of the eye, takes in visual information and sends it to other parts of the brain using the optic nerve. In this case, the optic nerve prompts the pineal gland to get to work releasing melatonin. This connection of sunlight to the release of melatonin is crucial to keeping us on a healthy sleep schedule.
By Priyanka Walker
When the Sun sets on the horizon, cities around the globe slow down, people begin to yawn, and bedtime ensues. In contrast, when the Sun rises, the world repeatedly wakes. What causes this consistent sleep and wake cycle that coincides with dawn and dusk? Is it simply a universal human habit that most people continue to do because everyone else is doing it? No, it’s not a habit or a tradition handed down from our great-grandparents’ great-grandparents. Like many things, science explains that our tendency to follow this pattern is deeply rooted in both our physiology and our body’s connection to its environment. Our desire to sleep when it’s dark and to rise when it’s light is due to a complex and fascinating phenomenon called the circadian rhythm, a twenty-four-hour cycle connected to our exposure to sunlight as well as the activation of several hormones within us.
To understand circadian rhythm, one has to first understand melatonin, the sleep hormone. Hormones are the chemical messengers our body uses to initiate activity in various anatomical systems. In this case, the hormone melatonin triggers our bodies to transition into sleep mode, and then the hormone continues to be produced for several hours each evening, reminding several of our bodily systems to remain in resting state.
Melatonin is released from tissue all over the body, but the primary producer of this sleepy-time hormone is a part of the brain called the pineal gland. The pineal gland usually starts producing melatonin around 9 p.m. as long as it is uninhibited by human routines such as nightshift schedules, bright light, or travel to different time zones (also known as “jet lag”). Melatonin levels at night in a healthy human are typically ten times what they are during the day. It’s no wonder that it can be extremely difficult to fight off sleep at night—there’s an entire army of hormones at work.
When this blast of nighttime melatonin takes place in the pineal gland, it uses the circulatory system to carry melatonin through the blood to various parts of the body that have melatonin receptors. When these receptors receive melatonin, they respond in a variety of ways. For example, the heart rate slows and the body temperature lowers which both encourage relaxation so that sleep takes place. Eventually, melatonin stops being released (it is typically sometime around 6:30 a.m.), and these same body systems start waking up. Later in the day, the process repeats itself again starting with the melatonin release from the pineal gland.
Clearly, melatonin is tightly linked to our circadian rhythm, but what causes the pineal gland to kick into action and start releasing melatonin? You probably guessed it—it’s the Sun that triggers this entire process. Sunlight hits our eyes, and even more specifically, it hits the retina. It may surprise you to find out that our eyes are actually a part of the brain—a very important part at that! Your retina, the innermost lining of the eye, takes in visual information and sends it to other parts of the brain using the optic nerve. In this case, the optic nerve prompts the pineal gland to get to work releasing melatonin. This connection of sunlight to the release of melatonin is crucial to keeping us on a healthy sleep schedule.
Answers
Answer
According to Passage 1, which of the following is MOST responsible for people’s tendency to sleep during the dark and wake when it is light?
Acircadian rhythm
Bpineal gland
Cmelatonin
Dhabits
Acircadian rhythm
Bpineal gland
Cmelatonin
Dhabits
Answered by
GPT-4o mini
The passage discusses the relationship between sunlight, melatonin, and the sleep-wake cycle known as the circadian rhythm. It emphasizes that our sleep patterns are not merely habits but are fundamentally influenced by physiological processes tied to hormonal activity. Melatonin, the primary sleep hormone produced by the pineal gland, plays a crucial role in initiating and maintaining sleep. Its production typically begins around 9 p.m. and stops around 6:30 a.m., creating a natural rhythm in line with the day-night cycle.
The passage highlights how sunlight impacts this process: light entering the eyes affects the retina, which sends signals to the brain, ultimately triggering the pineal gland to regulate melatonin release. Thus, exposure to light is essential for managing melatonin levels and, consequently, our sleep patterns. In summary, the passage outlines the scientific explanation for our inclination to sleep at night and be awake during the day, attributing it to the interaction between sunlight and hormonal activity in the body.
The passage highlights how sunlight impacts this process: light entering the eyes affects the retina, which sends signals to the brain, ultimately triggering the pineal gland to regulate melatonin release. Thus, exposure to light is essential for managing melatonin levels and, consequently, our sleep patterns. In summary, the passage outlines the scientific explanation for our inclination to sleep at night and be awake during the day, attributing it to the interaction between sunlight and hormonal activity in the body.
Answered by
GPT-4o mini
According to Passage 1, the factor that is MOST responsible for people's tendency to sleep during the dark and wake when it is light is **A) circadian rhythm**. The passage explains that this sleep-wake cycle is linked to our physiology and is influenced by the exposure to sunlight and the release of hormones such as melatonin, but it is the circadian rhythm that encompasses these processes.
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