Topic 9 - Sleep and dreaming Flashcards
What is sleep?
A condition of body and mind that occurs several hours a night where:
- the nervous system is inactive
- eyes are closed
- postural muscles are relaxed
- consciousness is suspended
How is brain activity measured?
Electroencephalogram (EEG)
What are the first four stages of sleep called?
NREM sleep - non rapid eye movement sleep.
What is the 1st stage of NREM and what happens?
1st stage - sleep onset
- lightest stage of sleep (easily woken up in this stage)
- Alpha brain activity is resting and theta waves shows periods between wake and sleep.
- Muscles are less active - less eye movement.
What is the 2nd stage of NREM and what happens?
2nd stage - Late night stage
- Eye movement stops.
- Heart rate drops.
- Body temperature drops.
- Theta waves are slower.
- Burst of brain activity (sleep spindles)
What is the 3rd stage of NREM and what happens?
3rd stage - deep sleep
- Between light and deep sleep.
- Slow delta brainwaves, but also faster ones.
- Difficult to wake up.
What is the 4th stage of NREM and what happens?
4th stage - deep sleep
- Slow delta waves.
- No eye movements.
- When awoken may feel disorientated.
- Children can experience sleepwalking or night terrors when in deep sleep.
What is REM sleep?
REM - rapid eye movement sleep.
REM is caused by eyes moving a lot behind the eyelids when dreaming occurs. About 20% of our sleep is REM, and 50% for infants.
What happens during REM sleep?
- Dreaming occurs in REM sleep for around 2 hours.
- All incoming sensory information is blocked (sensory blockade).
- Movement inhibition (pons send out signals in the base of the brain which shuts off neurons in the spinal cord, preventing movement).
- Rapid, shallow, irregular breathing.
- Eyes jerking (caused by eyes moving a lot behind the eyelids when dreaming).
- Heart rate and blood pressure rise.
- The brain processes, consolidate, and stores information into long-term memory.
How many cycles of sleep do we experience in a night?
- About 5 cycles of the 4 stages and REM.
- One cycle lasts around 90 mins.
- First cycle has short REM period, more deep sleep.
- As cycle progresses longer REM and shorter less deep sleep.
- In the morning, mostly in stages 1 and 2.
What are the benefits and functions of sleep?
- Deep sleep can help to avoid the breakdown of proteins.
- REM sleep stimulates learning and increases proteins.
- Sleep can help neurons repair themselves.
What is sleep deprivation?
Not having enough sleep (decrease in amount, consistency and quality). This can affect physical functioning, such as weight and brain functioning.
What are the two different rhythms in our body that are associated with sleep?
- Circadian Rhythms
- Ultradian rhythms
What are Circadian rhythms?
Human body rhythms (aka the body clock) that have a 24-hour cycle, and are reset by levels of light, such as the sleep cycle.
What controls the circadian rhythm?
The suprachiasmatic nuclei (SCN).
What are Ultradian rhythms?
A biological rhythm that repeats more frequently than once every 24 hours, such as the sleep cycle.
What are biological rhythms regulated by?
-Endogenous pacemakers
-Exogenous zeitgebers
What is an endogenous pacemaker?
- External cues that may affect or entrain our biological rhythms, such as the influence of the suprachiasmatic nucleus on the sleep/wake cycle.
What is an exogenous Zeitgeber?
-An exogenous zeitgeber is an external cue from the outside world that keeps our internal body clock to time.
Explain the sleep/wake cycle.
- The effect of daylight (exogenous zeitgeber) on sleep/wake cycle is why we are drowsy at night and alert in the day.
- It is governed by internal pacemaker, a body clock called the suprachiasmatic nucleus (SCN)
- The SCN lies just above the optic chiasm which provides information from the eye about light, exogenous zeitgebers can reset the SCN.
Describe Siffre’s case study.
- Spent several extended period underground to study the effects on his own biological rhythms, deprived of exposure to natural light and sound
- Spent 2 months in southern alps, thought he had only spent a month
- Spent 6 months in texan cave
- His ‘free-running’ biological rhythm settled down to one that was just beyond the usual 24 hours, though he did have regular falling asleep cycle
Explain ultradian rhythm of the sleep cycle
- Identified 5 distincts stages of sleep that altogether span 90 minutes , a cycle that continues through the night.
- Each stage is characterised by a different level of brainwave activity which can be monitored using an EEG .
Evaluate ultradian rhythms
STRENGTH: improved understanding of age-related changes in sleep.
-sleep scientists have observed that slow wave sleep reduces with age , growth hormone is produced mostly during SWS therefore this is reduced in older people.
LIMITATION: ultradian rhythms research is there is significant variation between people
Evaluate circadian rhythms
STRENGTH: it provides an understanding of the adverse consequences that occur when they are disrupted (desynchronisation).
LIMITATION: generalisations are difficult to make
-studies are based on a very small samples of participants it seems that sleep wake cycles may vary widely from person to person.
Describe light as an exogenous zeitgeber
- Light is a key zeitgeber in humans, it can reset the body’s main endogenous pacemaker, the SCN and plays role in maintenance of sleep/wake cycle
What is the SCN?
- Suprachiasmatic nucleus
- The suprachiasmatic nucleus (SCN) is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain.
- It is one of the primary endogenous pacemakers in mammalian species and is influential in maintaining circadian rhythms such as sleep/wake cycle.
- Receives info about light directly from this structure, continues even when our eyes are closed enabling the biological clock to adjust to changing patterns of daylight whilst we are asleep.
What is the pineal gland?
- A small endocrine gland in the brain that regulates melatonin production in response to darkness.
What is melatonin?
- A hormone released in response to darkness, helping regulate sleep.
- Melatonin levels rise in the evening, peak at night, and decrease in the morning.
Describe light as an exogenous zeitgeber.
- The main external zeitgeber that regulates circadian rhythms by influencing the SCN and melatonin production.
- Light resets the SCN, keeping circadian rhythms aligned with the external environment.
