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Summary Sleep Cycles and Circadian Rhythms
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All stages of sleep and their potential functions discussed in relation to circadian rhythms. Pineal Gland discussed
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Chapter 14 – sleep, dreaming and circadian rhythmsPeople sleep a lot. EEG (electroencephalograms), EOGs (electrooculogram) and (EMGs)
(electromyograms) all help map the stages of sleep. They measure brain wave activity, eye
movements, and neck movement. In sleep studies, many days are spent just getting used to the
environment and sleeping well before the study commences.
- Beta waves are predominant when awake, but as one descends into stage 1 sleep, there are
alpha waves acting. These are low voltage, high frequency waves that resemble an awake
state.
- Stage 2 has high amplitude, low frequency waves. There are also sleep spindles and k
complex waves. K complex is a large negative wave, followed by a single positive wave. The
sleep spindles are 0.5 – 3 second busting and booming waves of high frequency.
- Delta waves are in stage 3. These waves are slow and long. When reverting to stage 1 from
this stage, the eye movement and loss in muscle tone is more evident, suggesting the person
will stay asleep. Each cycle, going from stage 1 – 2 – 3 – 1 – 2… occurs every 90 minutes.
People stay in the first stage as the night progresses. Emergence into stage one sleep again is
called REM sleep. Being in REM sleep causes genital arousal, heightened pulse, higher rates
of respiration and neural firing, which may be responsible for dreams.
Dreaming
Waking from REM sleep – 80% chance of dream recall – well recalled, narrated and descriptive
Waking in nREM sleep – 7% dream recall – tend to be about isolated experiences, like falling
Cortical lesions can abolish dreaming without affecting EM sleep whilst anti-depressants make it
hard to achieve REM sleep, but they still dream – they are not entirely co-existent.
Testing common beliefs about dreaming
External stimuli Dreams run on Some people No sexual dreams Sleep talking
incorporation in real time dream needed to have (somniloquy)
dreams infrequently erections in occurs in any
dreams stage
When spraying We are aware They are advised Even babies get Sleep walking
participants with how long they to write down erections in REM (somnambulism)
water, upon may have lasted any instances of sleep never occurs in
awakening, half when waking up dreaming REM sleep, as
experienced muscle tone is
water in their lost
dreams
Can range from They tend to only Occurs in stage 3
mild to intense dream in REM usually
experiences sleep
, Interpretation of dreams
Sigmund Freud – dreams are repressed desires, often sexual. Manifesting dreams, what we dream,
are disguised versions of latent dreams, what we desire in real life. He is not entirely right, but there
has been a theory where dreams are the result of subconscious stress or emotion. Not necessarily
desires.
Activation synthesis model – during REM sleep, there are a lot of neural signals bombarding the
cerebral cortex. Dreams are then our brains trying to make sense of these random neural signals.
Like when we stare at clouds and say it looks like England. It is not actually England.
Why do we sleep and why do we sleep when we do?
Theories of sleep:
- Recuperation: being awake disrupts homeostasis, so sleep helps restore this. Two main
ideas focus on energy restoration and clearing toxins that accumulate during wakefulness.
- Adaptation: humans usually sleep at night regardless of what happens during the day due to
a 24-hour rhythm. This could serve evolutionary purposes, where we sleep to conserve the
resources lost during the day, like energy and muscle exhaustion. But, sleeping at night is
dangerous, so the exact reason is unknown. Some adaptation theories suggest we sleep for
fun.
Comparative analysis of sleep
Most mammals and birds’ sleep. Sleep is not a high order function, nor is it necessary to protect
animals from mishap. Some animals sleep way longer than others, cats sleeping 14 hours a day and
horses sleeping for two hours. This goes against the recuperation theory, as sloths do nothing all day
but still sleep a lot. Sometimes, animals must sleep less to avoid predators from killing them or to
access scarce food resources.
Effects of sleep deprivation
Interpreting sleep deprivation is difficult as sometimes it is hard to differentiate between adverse
effects of sleep deprivation or natural day-to-day stress or stress from doing a study. This stress can
also make people agitated and winded up, like sleep deprivation symptoms. This then means the
stress could be causing these issues not the sleep deprivation.
Recuperation theories helps us understand three main issues with sleep deprivation:
- Long periods of wakefulness cause behavioural disturbances
- These disturbances worsen the longer one is awake
- Missed sleep is regained after a night’s rest
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