Ashwin Lewis
Sleep is a necessary function that helps restore the body and is controlled by an area of the brain called the SCN (suprachiasmatic nucleus). The SCN is located in the hypothalamus and is sensitive to signals of dark and light. Sleep/wake cycles are triggered by chemicals in the brain called neurotransmitters, which send messages to different nerve cells in the brain. Waking up in the middle of the night is normal, but it can become problematic as it interrupts sleep, which can impair cognitive function. Parasomnias are a type of sleep disorder characterised by behaviours or events that disrupt sleep, such as sleepwalking, sleep terrors, and confusional arousals.
| Characteristics | Values |
|---|---|
| Sleep/wake cycles | Controlled by sleep/wake homeostasis and the circadian biological clock |
| Sleep/wake homeostasis | The longer you are awake, the greater your body senses the need to sleep |
| Circadian biological clock | Causes highs and lows of sleepiness and wakefulness throughout the day |
| Sleep/wake cycle controlled by | The SCN (suprachiasmatic nucleus) in the hypothalamus |
| Sleep/wake cycle influenced by | Neurotransmitters |
| Neurotransmitters | Help your body recharge while you sleep |
| Can help you remember things that you learned, heard, or saw while you were awake | |
| Can work against you and trigger sleep disorders | |
| Sleep disorders | Sleep terrors, sleepwalking, sleep paralysis, parasomnias |
| Sleep deprivation | Can lead to a decrease in performance, mood, and thinking |
| Sleep tips | Turn your alarm clock to face the wall; don't check the time on your smartphone; don't stay in bed; make your room cool and dark |
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What You'll Learn
Sleep disorders and parasomnias
Parasomnias can be classified into two main types: non-rapid eye movement (non-REM) and rapid eye movement (REM) parasomnias. Non-REM parasomnias, also known as "disorders of arousal", are more common in children. During these episodes, individuals partially wake up, with their eyes open and appearing to act with intention. However, they may not respond to external stimuli and may have no memory of the event afterward. Examples of non-REM parasomnias include sleepwalking, night terrors, and sleep-related eating disorders. Sleepwalking, or somnambulism, involves partial awakening and complex motor behaviours such as walking, running, or talking. Night terrors, or sleep terrors, are episodes of fear, confusion, and screaming during sleep. Sleep-related eating disorders drive people to eat and drink in their sleep, sometimes consuming inedible or toxic substances and risking injuries from food preparation.
REM parasomnias, on the other hand, occur during the REM stage of sleep, which is characterised by rapid eye movements, increased brain activity, faster and irregular breathing, and increased heart rate and blood pressure. Dreams mostly occur during this stage. Examples of REM parasomnias include REM sleep behaviour disorder (RSBD), in which individuals act out their dreams through vocalisations or aggressive movements, and nightmares, which are frightening dreams that cause sleepers to wake up suddenly and anxiously. Nightmares are typically more common in adults and are often linked to conditions such as post-traumatic stress disorder, depression, or schizophrenia.
Parasomnias can have various causes and risk factors. They can be influenced by genetic factors, with a higher likelihood of occurrence if there is a family history of parasomnias. Additionally, certain medications, such as specific antidepressants, can increase the likelihood of parasomnias. Underlying neurological disorders and diseases, including narcolepsy, multiple sclerosis, Parkinson's disease, and dementia, can also contribute to the development of parasomnias. Stress and anxiety are other factors that can trigger parasomnias, with stress being a known provocateur of nightmares.
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Sleep/wake cycles and internal clocks
Sleep/wake cycles are triggered by chemicals in the brain called neurotransmitters. These send messages to different nerve cells in the brain. Neurotransmitters such as norepinephrine, histamine, and serotonin act on parts of the brain to keep it alert and functioning while a person is awake. Other nerve cells stop the messages that tell a person to stay awake, causing them to feel sleepy. One such chemical is adenosine, which slowly builds up in the blood while a person is awake and dissipates while they sleep. Caffeine promotes wakefulness by blocking the receptors to adenosine.
The sleep/wake cycle is also regulated by the body's internal clock, which is controlled by an area of the brain called the suprachiasmatic nucleus (SCN). The SCN is located in the hypothalamus and is sensitive to signals of dark and light. When darkness falls, the SCN sends messages to the pineal gland, which triggers the release of the chemical melatonin. Melatonin makes people feel sleepy and ready for bed. During the day, the SCN triggers the release of cortisol and other hormones to help people wake up.
Two internal biological mechanisms—circadian rhythm and homeostasis—work together to regulate when a person is awake and when they are asleep. Circadian rhythms direct a wide variety of functions, from daily changes in wakefulness to body temperature, metabolism, and the release of hormones. With sleep/wake homeostasis, the longer a person is awake, the greater their body senses the need to sleep. If this process alone controlled the sleep/wake cycle, a person would feel the most energy after a full night's rest and be tired and ready for sleep at the end of the day. However, the circadian biological clock causes highs and lows of sleepiness and wakefulness throughout the day. Typically, most adults feel the sleepiest between 2 a.m. and 4 a.m. and also between 1 p.m. and 3 p.m.
Getting regular, adequate amounts of sleep is important. It can help people feel awake and refreshed during the day and relaxed and sleepy at night. However, even losing just one hour of sleep over a few days can lead to decreased performance, mood, and thinking.
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Sleep stages and brain activity
Sleep is a complex process that involves the interaction of various parts of the brain and a multitude of chemicals and neurons. The brain controls the transitions between wakefulness and sleep through several mechanisms. The basal forebrain, located near the front and bottom of the brain, promotes sleep and wakefulness. The midbrain, on the other hand, helps us stay alert during the day. The release of a chemical called adenosine from cells induces sleepiness, while caffeine counteracts this effect by blocking adenosine receptors.
There are two primary types of sleep: rapid-eye movement (REM) sleep and non-REM sleep. Within non-REM sleep, scientists have identified three distinct stages, each associated with specific brain waves and neuronal activity. During a typical night, we cycle through non-REM and REM sleep several times, with the REM periods becoming longer and deeper as the night progresses.
Stage 1 non-REM sleep marks the transition from wakefulness to sleep. It is characterised by slow brain waves, relaxed muscles, and occasional twitches. This stage usually lasts a few minutes and accounts for about 5% of total sleep time.
Stage 2 non-REM sleep is a period of light sleep before entering deeper sleep. The body temperature drops, eye movements cease, and breathing and heart rate slow down. Brain wave activity also slows down but is punctuated by brief bursts of electrical activity. This stage constitutes the majority of repeated sleep cycles.
Stage 3 non-REM sleep, also known as deep sleep, is crucial for feeling refreshed in the morning. It occurs mostly during the first half of the night, with longer durations in the initial stages. During this stage, the heart rate, breathing, and body temperature reach their lowest levels, and it becomes challenging to wake the sleeper. Brain waves during this stage are identified as delta waves, making it also known as delta sleep or slow-wave sleep.
REM sleep typically occurs about 90 minutes after falling asleep. During this stage, the eyes move rapidly behind closed eyelids, and brain wave activity resembles that of wakefulness. Dreaming predominantly occurs during REM sleep, and the amygdala, involved in processing emotions, shows heightened activity. REM sleep is believed to be vital for memory and other cognitive functions.
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Sleep deprivation and health
Sleep is a basic human need, as essential as eating, drinking, and breathing. Sleep deprivation occurs when an individual does not get enough sleep, and it can have a significant impact on both physical and mental health.
The human body has an internal clock, controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus, which regulates the sleep/wake cycle. This cycle is influenced by the exposure to light and darkness, with the SCN triggering the release of cortisol and other hormones to help us wake up and sending messages to the pineal gland to release melatonin, which induces sleepiness, when it is dark. The sleep/wake cycle also involves neurotransmitters, which send messages to different nerve cells in the brain, and the basal forebrain, which promotes sleep and wakefulness.
Sleep deprivation can have a range of negative consequences. It can lead to decreased performance, mood, and cognitive abilities, including concentration, learning, and memory consolidation. It can also cause mood swings, irritability, and compromised decision-making and creativity. Prolonged sleep deprivation can even lead to hallucinations and trigger mania in individuals with bipolar mood disorder. It is also associated with an increased risk of accidents due to delayed signals and reduced coordination.
Sleep deficiency, a broader concept than sleep deprivation, has been linked to chronic health issues, including heart disease, kidney disease, high blood pressure, diabetes, stroke, obesity, and depression. It can disrupt processes that maintain cardiovascular health, such as blood sugar regulation, blood pressure control, and inflammation levels. Sleep also plays a crucial role in the body's ability to heal and repair blood vessels and the heart. Additionally, sleep affects hormone production, with testosterone production, for example, requiring at least three hours of uninterrupted sleep.
Getting adequate and regular sleep is essential for maintaining overall health and well-being. It helps individuals feel refreshed and energized during the day and prepares them for a restful night's sleep.
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Sleep and temperature regulation
Sleep is a complex process that involves the coordination of various physiological and behavioural systems. One of the key aspects of sleep is temperature regulation, which is intricately linked to sleep quality and our sleep-wake cycles.
The human body has an internal clock, known as the circadian biological clock or circadian rhythm, which regulates our sleep-wake cycles. This internal clock is controlled by the suprachiasmatic nucleus (SCN), a structure within the hypothalamus, a peanut-sized region of the brain. The SCN is sensitive to light and dark signals, and it plays a crucial role in maintaining our behavioural rhythm by receiving information about light exposure from our eyes.
Our body temperature follows a daily rhythm, with fluctuations that influence our energy levels and sleep patterns. After waking up, the hypothalamus gradually increases our body temperature from its baseline of 98.6°F to about 100.4°F, helping us feel alert and energised. However, as bedtime approaches, our internal temperature starts to drop, making us feel drowsy and tired.
During sleep, our body temperature continues to fluctuate. In the first half of the night, our body temperature drops, coinciding with the period when we experience deep sleep. This cooler body temperature promotes muscle repair, growth stimulation, and improved immune function. During the second half of the night, our body temperature begins to rise, and this is when we typically experience more REM sleep, which is important for memory consolidation, emotional processing, and creativity.
To optimise sleep quality, it is essential to maintain a comfortable body temperature throughout the night. Overheating during sleep can interrupt rest and cause discomfort, while a cooler environment can enhance deep sleep. Various factors influence body temperature during sleep, including bedding materials, mattress type, and external temperature. Synthetic bedding materials, such as polyester, tend to trap heat, while natural fibres like cotton, linen, or wool are more breathable and effective in wicking away moisture. In terms of mattresses, innerspring and hybrid models are often recommended for temperature regulation due to their breathability and airflow. Additionally, timing activities like exercise and bathing can impact body temperature and sleep quality, with morning workouts and warm evening baths promoting better sleep.
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Frequently asked questions
Parasomnias are disruptive behaviours or events that affect your sleep. Examples include sleepwalking, sleep terrors, and sleep paralysis.
Sleep/wake cycles are triggered by chemicals in the brain. Chemicals called neurotransmitters send messages to different nerve cells in the brain. Nerve cells in the brainstem release neurotransmitters, including norepinephrine, histamine, and serotonin, which keep the brain alert and working well while you are awake.
If you wake up in the middle of the night, it is recommended to not stay in bed and to only go back to bed when you feel drowsy. It is also important to make sure your bedroom is cool, dark, and comfortable.
