Sleep And Dreams Flashcards
What is the circadian Rhythm?
Changes in humans hormone levels, body temperature and heart, respiration and metabolic rate over a 24hr cycle
What does the circadian sleep-waking rhythm determine? and what is it regulated by in humans?
The circadian sleep-waking rhythm determines our alertness and activity levels during the day and night. In humans it is regulated by:
- The endogenous (internal) pacemakers of the
- suprachiasmatic nucleus (SCN)
- Pineal gland - External resetters (zeitgeber)
- light, which is detected at the retina and can influence
- sound
The SCN
- The suprachiasmatic nucleus (SCN) is in the hypothalamus of the brain
- it lies at the point where the 2 optic nerves extending from each eye meet (in a shallow impression called the optic chiasm).
- therefore the SCN is highly influenced by the imput of light
- the SCN sends messages to the pineal gland to regulate its melatonin production
The pineal gland
- the pineal gland is situated in the centre of the brain and is approximately the size of a pea.
- when darkness falls, the SCN informs the pineal gland
- the pineal gland secretes the hormone melatonin which is the body’s natural sleeping drug
- relating to the zeitgeber of light, this is because light regulates the production of melatonin which is produced between 9pm and 7.30am which causes us to feel drowsy and sleepy.
- melatonin in turn affects the production of seratonin
- seratonin then concentrates in the raphe nuclei (sited near the pons).
- the raphe nuclei secretes a substance that affects the reticular activating system (RAS) to induce light sleep
- evidence comes from a study by jouvet (1976) who found that lesions on the raphe nuclei causes severe insomnia in cats
What controls melatonin production and where is melatonin produced?
-the SCN controls melatonin production but melatonin is produced from the pineal gland
What is melatonin and why is it special?
Melatonin is a hormone and is special because it’s secretion is dictated by light and is secreted into the bloodstream when it starts to get dark
What are the two primary functions of melatonin?
- to help control your circadian rhythm
- regulate certain reproductive hormones
What affect does melatonin production have on a person?
Melatonin makes a person feel drowsy, and eventually fall asleep.
What stops the release of melatonin?
Light exposures stops the release of melatonin, and in turn, this helps control your circadian rhythm.
When do melatonin levels peak?
- Melatonin levels peak in the middle of the night and then decrease towards daytime
- melatonin secretion is low during the daylight hours and high during dark periods
What is another chemical that affects sleep?
Adenosine
How does adenosine work?
- adenosine is created over the course of the day, as a natural byproduct of using up our internal energy stores.
- Adenosine builds up in our neurons during the day, which causes us to gradually feel more tired as the day goes on.
What happens when we sleep- Adenosine
When we sleep, this buildup is cleared and the levels of adenosine in the body rapidly declines and the adenosine in cells gets replaced by energy
Key research study- Czeisler et al 1990
Exposure to bright light and darkness during night work
Czeisler et al 1990- Aim
- To discover whether exposure to exceptionally bright light - a zeitgeber- in the night shift workplace and then total darkness for daytime sleep reset the circadian rhythm
- To help find a way to help night shift workers cope better with changing shift patterns
Czeisler et al 1990- Method
Lab experiment which attempted to increase ecological validity
Czeisler et al 1990- Participants
8 men, 22-29 yrs old, all healthy. None had done previous night work, none took alcohol or caffeine during study.
Czeisler et al 1990- procedure
A 2 week study:
Week 1- no night shift but participants had body temperatures and salivary content of melatonin measured at different times of day and night
Week 2- participants reported to the lab with their usual work load at 9pm and finished work at 5am
Czeisler et al 1990- IV1
Participants worked in rooms lit by bright lights ( at the intensity of natural sunlight) and given clear sleep instruction- to remain in the dark from 9am to 5pm in bedrooms in which light was excluded (they were given blackout blinds for their bedrooms)
Czeisler et al 1990- IV2
Participants worked the night shift in rooms lit by ordinary lights and given no instructions for sleep after work (during the day) all participants had meals provided for them
Czeisler et al 1990- DV
Measurements to track participants circadian rhythm:
- temperature
- saliva, to measure content of cortisol and melatonin concentration
- Urinary excretion rate
- score in alertness test
- score in mental maths test
Czeisler et al 1990- Results
- The experiment group slept 2 hours more each day than the control group
- After 6 days, the experimental condition found their circadian rhythm ha completely flipped to suit night shift. But those of the control group showed little or no change. This was shown because melatonin, cortisol concentration and urinary excretion rate synchronised with the night work schedule so that these were similar to their previous daily circadian rhythm in the experimental group but remained the same as the week 1 measurements of the control groups.
- Scores in the alertness and mental maths tests in the experimental group were higher that the control group from midnight to 8am
Czeisler et al 1990- conclusions
- Human circadian rhythm can be adapted to shift work if treated with very bright light at night and darkness during the day.
- This research provides evidence that use of very bright lights can reset body rhythms within 3 days- body temperature and hormone production is reset as very bright light mimics the effect of daylight. Bright lights entrain all rhythms not just the sleep-wake cycle
- Night shift workers should have very bright light to work in
What are the two main types of sleep?
- non REM sleep
- REM sleep
Stages of Non-REM sleep
There are 4 stages of slow wave non-REM sleep
Stage 1 approx duration (10mins)
-heart rate slows, muscles relax and you can still be worken easily
-hallucinations occasionally occur
Stage 2 approx duration (15mins)
-deeper sleep but still can be woken easily
-EEG patterns have larger and slower waves with bursts of fast spiking activity (called sleep spindles)
Stage 3 approx duration (20mins)
-deep sleep unresponsive to external stimuli, heart rate, blood pressure and body temperature drop
-EEG shows large slow delta waves
Stage 4 approx duration (45mins)
-very difficult to wake
-EEG shows only large slow delta waves
-sleepwalking can occur
EEG
EEG (electroencephalograph) was introduced in the 1930s to allow psychologists to understand more about sleep
Stages of REM sleep
There is just one stage of REM approx duration (25mins)
- EEG activity shifts into a fast desynchronised pattern similar to being awake
- the individual is hard to wake
- muscles relax completely, leaving the person paralysed
- heart rate and respiration increase
- rapid eye movements of the eye occur
How many times are the stages of sleep cycled around per night and how long does a sleep cycle last?
The stages of sleep are cycled through around 5 times per night. Each sleep cycle lasts approximately 90mins
Dement and Kleitman 1957- Aim and 3 aims
To provide an objective study of rapid eye movement in relation to the experience of dreaming
- Does dreaming take place during R.E.M?
- Are participants aware of length of dreams 5 or 15mins?
- Does eye movement direction relate to dream content
Dement and Kleitman 1957- Participants
7 adult males and 2 females which were all volunteers
Dement and Kleitman 1957- research method
Laboratory experiment using observation
Dement and Kleitman 1957- procedure
- subjects slept individually in a quiet dark laboratory room after a normal day’s activity
- alcohol and caffeine were avoided during the days
- electrodes were connected on scalp to measure brain waves and near the eyes to register rapid eye movement
- subjects were awoken at various time during the night by a loud doorbell noise, and immediately reported into a recording device: whether they had been dreaming
- dreaming was only counted if a fairly detailed and coherent dream was reported