Purpose of Sleep and the Sleep Wake Cycle

What is sleep?

Periods of partial or total altered/loss of conciousness in which mental and physical activity are reduced

What are the two main reasons why humans became motivated to sleep during the night according to adaptation theories of sleep?

Evolutionary Theory of Sleep

Restorative Theory of Sleep

What does evolutionary theory of sleep suggest?

Early humans used the daytime rather than nighttime to eat, drink and reproduce as there was greater risk of injury in the dark, and night time predators could threaten their survival

Believes that periods of inactivity evolved as a means of conserving energy

Sleeping at night allowed for energy to be conserved

What does Restorative Theory of sleep suggest

Recuperation theories of sleep claim that homeostasis of the body (the ability to balance internal physiological functioning) is disrupted when humans are awake and that sleep acts to restore it

Sleeping allows the energy levels that decline during wakefulness to be restored

We sleep more when we are sick. When we don’t sleep enough, we are more likely to get sick

Cell division and protein synthesis increases in the body during sleep

Therefore, this theory believes that sleep will repair and restore your basic body functions and strengthen the immune system

What dimensions of health does sleep restore?

Physical restoration

Cognitive function

Immune Support

Emotional Regulation

How does sleep aid in physical restoration

·- homeostasis of the body (the ability to balance internal physiological functioning) is disrupted when humans are awake and that sleep acts to restore it.

How does sleep aid in cognitive function

Sleeping allows the energy levels that decline during wakefulness to be restored.

How does sleep aid in immune support?

Sleeping allows the energy levels that decline during wakefulness to be restored.

How does sleep aid in emotional regulation?

Sleep helps regulate emotions and maintain mental health. It allows for the processing of emotional experiences and stress, reducing anxiety and enhancing mood stability.

What is the Sleep-Wake cycle?

The recurring 24 hour pattern of wakefulness and sleep

It typically consists of approximately 16 hours of daytime wakefulness and 8 hours of nighttime sleep

This cycle is usually measured by recording times of regular events, such as when we eat and go to sleep

What are the key components of the sleep-wake cycle?

Circadian rhythm

Melatonin

What is the sleep wake cycle regulated by?

The circadian rhythm and is regulated by body temperature, metabolic rate and the release of hormones including melatonin

What is the circadian rhythm?

A natural bodily cycle that repeats approximately every 24 hours and responds to external environmental rcues

What is the sleep circadian rhythm?

natural bodily cycle that regulates the timing of sleep and wakefulness, as well as other physiological processes such as hormone production, body temperature and digestion. It follows a roughly 24-hour cycle and is influenced by external environmental cues, such as light and darkness.

What are most circadian rhythms regulated by?

Master circadian clock that functions to coordinate biological processes so that they occur at a time that maximises the fitness of an individual

Where is the master circadian clock located?

In the hypothalamus of the brian in a cluster of about 20,000 neurons called the suprachiasmatic nucleus

Neurons get input about the duration and intensity of light detected by the eyes and coordinate the timing of the body’s circadian rhythms

How can circadian rhythms be reset?

Can be reset by exposure to external stimuli such as heat and light, for example, after travelling across time zones, people typically experience get lag before their circadian clock becomes in sync with local time

What are the different types of circadian rhythms

These include the body temperature cycle, in which body temperature naturally drops at night and rises during the day

hormone secretion cycles

digestion and metabolism cycle

sleep wake cycle

while body temperature, melatonin secretion and cortisol secretion are separate circadian rhythms that each follow their own roughly 24 hour cycles, they are tightly linked and help regulate the sleep wake cycle

What is melatonin?

A hormone secreted by the pineal gland that helps regulate the sleep wake cycle by increasing in the evening to promote sleepiness adn decresing in the morning to support wakefulness.

produced by the pineal gland in response to darkness

What is cortisol?

Hormone released by the adrenal glands which peaks in the morning to help us wake and decreases at night to allow rest

What are the stages of the sleep-wake cycle?

Non-REM and REM sleep

There are 4-6 sleep cycles that last approximately 90 minutes each, however the sleep cycles alter in length as does the time spent in each stage

NREM 1 NREM 2 NREM 3

four distinct stages

• 3 are NREM

• 1 REM

A person typically goes through NREM1, NREM2, NREM3, NREM2,NREM1, REM, then back to NREM2

What is NREM Stage 1