Sleep is crucial to our ability to survive: it is the periodic, reversible loss of consciousness. Through our body’s circadian rhythm, our bodies are regulated in a 24 hour cycle, and when sleep does occur, it is in a 90 minute cycle of REM sleep. Sleep has many imperative functions for survival, yet many individuals face sleep disorders.
Our body has a circadian rhythm, which is a biological clock that occurs on a 24 hour cycle. The cycle is altered by and experience and influences body temperature, arousal, and energy throughout the day.
At around 2am is the deepest sleep, with the lowest body temperature around 4:30 am. Around when we wake up, about 6:45 am, there is the sharpest rise in blood pressure: over the next few hours, melatonin secretion stops, bowel movement likely occurs, there is the highest testosterone secretion and the highest alertness. Between noon and 6pm, is the best coordination and fastest reaction time. Once, it is back to the time we go to sleep, melatonin secretion and bowel movements are suppressed.
Our sleep patterns are both genetically and culturally influenced. Technology has also influenced sleep as blue light from screens activates light sensitive retina protons that trigger signals to suprachiasmitic nuclei, which then decrease the amount of melatonin from the pineal gland. Overall, looking at screens causes the body to respond to light and suppress the melatonin secretion, which is necessary to sleep.
When we are sleeping, we cycle through different stages of sleep, from NREM-1, which features hypnagogic sensations. These false sensory experiences, such as a visual stimulus or the feeling of falling. The first stage marks the transition between wakefulness and sleep, where the muscles relax and the heart rate, breathing, eye movements, and brain waves begin to slow down: this lasts several minutes. Next, is the NREM-2 stage which is where most time is spent during sleep. In this stage, are the sleep spindles which are bursts of rapid, rhythmic brain wave activity. Heart rate and breathing continue slowing down, while eye movements will cease and body temperature decreases. In NREM-3, we are in a deep sleep during which large, slow brain waves, called delta waves, are emitted. Heartbeat, breathing, and brain waves reach their lowest level during this stage, which allows us to feel refreshed the next day. Finally REM, or rapid eye movement, is a recurring sleep stage lasting 90 minutes, during which vivid dreams commonly occur. This stage contains sleep paralysis because the muscles are relaxed, while bodily systems are still functioning.
During REM sleep, we have dreams, which are sequences of images, emotions, and thoughts. The content of dreams usually includes ordinary events or common themes of anxiety, such as failing or being attacked. There are many proposed explanations for why we dream. According to Sigmund Freud’s The Interpretation of Dreams, the manifest content of a dream is the remembered storyline, while the latent content is the underlying meaning of a dream. This “psychic safety valve” works to express otherwise unacceptable feelings with a hidden meaning. However, this existence of unconscious desires within dreams lacks scientific support. Another reason may be information processing as dreams help us consolidate memories of the day. Yet, a question remains: how can we dream of things we have not experienced?
There are also physiological theories, including REM sleep helping us to develop and preserve neural pathways, as well as trigger brain areas that process visual imagery. At the same time, a critical consideration of this theory is that it does not explain why we experience meaningful dreams. Also, the cognitive development theory argues that dreams represent the person’s level of cognitive development. This means that children’s dreams would be less complex, whether it be the language or subject, than an adult’s dreams.
Regardless of the reasons why we dream, all theories agree REM sleep is important. This is because REM rebound occurs following REM deprivation, showing that the body requires REM sleep and increases sleep when it is lacking.
There are many reasons why we require sleep:
- Sleep protects us and is rooted in survival with a species sleep pattern best suited to its ecological niche.
- Sleep helps us restore and rebuild our memories of the day by strengthening neural memory traces.
- Sleep helps the brain recuperate by restoring and repairing brain tissue.
- Sleep allows for creative thinking through ideas and dreams, and better problem solving, thinking, and learning.
- Sleep supports growth since the pituitary gland can secrete growth hormones for muscle development.
As a result of sleep’s importance for our physical and mental health, sleep loss can have major effects on our wellbeing. Sleep loss can be a predictor of depression because REM sleep helps process emotional experiences and protect against depression. Plus, the additional effects of sleep loss can contribute to depression, such as difficulty studying, fatigue, increased mistakes, decreased productivity. Sleep loss can also lead to weight gain as it increases ghrelin, a hunger arousing hormone, and cortisol, a stress hormone that stimulates the body to make fat. On a more serious level, sleep loss suppresses immune cells, making the body more susceptible to viral infection and cancer.
Sleep loss can be extremely dangerous in our everyday lives, especially with drivers’ fatigue that leads to slower reactions and increased errors on the road. According to the National Highway Traffic Safety Administration, drowsy driving was responsible for at least 91,000 car crashes and 795 deaths in the U.S. in 2017. In addition, sleep loss can lead to an increased risk of high blood pressure and increased inflammation in the joints.
One type of sleep disorder is insomnia, which is characterized by recurring problems in falling or staying asleep. People with insomnia also experience excessive daytime sleepiness, and must exhibit symptoms at least three times per week for at least three months. According to the Sleep Foundation, up to one-third of adults live with some form of insomnia. Sleep-onset insomnia occurs when people have difficulty falling asleep, whereas sleep maintenance insomnia is difficulty staying asleep (mixed insomnia is a blend of both). A common cause of insomnia is stress because when stressed, cortisol and adrenaline are released by the adrenal glands that inhibit sleep by forcing alertness. Many quick fixes for insomnia, such as sleeping pills, may only aggravate the problem by decreasing REM sleep and leading to tolerance.
Narcolepsy occurs when patients either feel an irrepressible urge to sleep or involuntary lapse into sleep everyday for at least three months. Sleep apnea is characterized by abnormal breathing which causes lower quality sleep. The three types of sleep apnea include obstructive sleep apnea (when the airway is physically blocked), central sleep apnea (the brain system controls respiration) or mixed (a blend of both). Some symptoms of sleep anea include disrupted breathing, headaches in the morning, daytime fatigue, limited attention span, and snoring: these may be caused by anatomical characteristics (like the size of one’s tongue), obesity, alcohol use, smoking cigarretes, sleep position, and congestion. The lack of oxygen balance in the body can lead to cardiovascular issues, including high blood pressure, heart disease,and stroke.
Sleepwalking and sleep-talking are NREM-3 sleep disorders that are most common in childhood. Sleepwalking is specifically when an individual moves out of their bed, and attempting to wake them may result in aggressive behavior. Night terrors are also mosty among children when they may cry or scream in their sleep, but have little memory of the incident.
Overall, sleep is crucial to the functioning of our brains and bodies, so it must be priortized in our lives. Based on our genetics and circadian rhythms, our sleep patterns will differ. However, the effects of sleep loss and sleep disorders demonstrate just how important adequate sleep is to our health and wellbeing.