Sleep: purpose & function

Question 1

A typical night of sleep is…

Answer 1

7-8 hours, in 1.5 hour sleep cycles

NREM periods decrease as the night progresses.
REM periods increase as the night progresses.

Question 2

What is NREM sleep?

Answer 2

Non-rapid eye movement sleep. As adults, we spend 80% of sleep in NREM

Question 3

What is REM sleep?

Answer 3

Rapid-eye movement sleep. As adults we spend 20% of sleep in REM.

Question 4

What is a circadian rhythm?

Answer 4

24 hour cycle. E.g. Sleep-wake cycle

Question 5

What is an ultradian rhythm?

Answer 5

Cycle that is less than 24 hours E.g. REM and NREM sleep cycles

Question 6

What is an infradian rhythm

Answer 6

Cycle that is more than 24 hours E.g. Menstrual cycle

Question 7

What is a circadian rhythm determined by?

Answer 7

Controlled by an internal body clock called the suprachiasmatic nucleus which is located in the hypothalamus, which monitors the release of melatonin from the pineal gland.

Question 8

What is melatonin?

Answer 8

A sleep hormone that is secreted from the pineal gland which is released when it is dark, and is stopped when it is light

Question 9

What affects the suprachiasmatic nucleus?

Answer 9

Exposure to light causes the suprachiasmatic nucleus to signal to the pineal gland to stop releasing melatonin.

> Light in the morning can lead to waking (phase shift)
Light in the evening can keep us awake (phase delay).

Question 10

In a full night’s sleep how do the NREM/REM stages transition?

Answer 10

> NREM 1
NREM 2
NREM 3
NREM 4

> NREM 3
NREM 2

> REM

Question 11

What happens in NREM 1?

Answer 11

> Transition between awake and being asleep

> Time: Between 30 seconds to 10 minutes

> Theta waves

> Hallucinatory images
Hypnic jerks (involuntary muscle twitches )
Easily awakened

Question 12

What happens in NREM 2?

Answer 12

> True sleep begins, first part of NREM/REM sleep cycle

> Time: 20 minutes

> More theta waves + k-complex waves (sharp rise and falls in amplitude) and sleep spindles (periodic bursts of rapid frequency)

> 50% of our total sleep
Fairly easily awakened
Eyes stop rolling and muscles more relaxed

Question 13

What happens in NREM 3?

Answer 13

> Brief transitional stage that makes the start of deep sleep

> Time: 20 minutes

> Delta waves

> Less responsive to external stimuli
If awoken, feel groggy
Eyes don’t move, muscles are relaxed, and heart rate and breathing rate are reduced

Question 14

What happens in NREM 4?

Answer 14

> Deepest sleep

> Time: 30 minutes in the 1st cycle, decreasing in duration

> Delta waves

> Extremely difficult to wake up someone
Conscious awareness is very low; sensitive to certain stimuli
Sleep walking, sleep talking, bedwetting, night terrors

Question 15

What happens in REM?

Answer 15

> Paradoxical sleep → active mind, paralysed body

> Time: 10 minutes in 1st cycle, increasing in duration

> Sawtooth waves are random, fast waves, also known as beta-like waves and are associated with dreaming.

> Repetitive bursts of rapid eye moving
Heart rate, blood pressure and breathing rate increase/fluctuate
No muscle tension → muscles are very relaxed that they almost appear paralysed (muscle atonia/cataplexy)

Question 16

What is the evolutionary theory of sleep?

Answer 16

It states that sleep is a means of increasing an animal’s chances of survival.

> Sleep depends on an animal’s vulnerability to predators. Prey tend to sleep less, especially when exposed in their environment, whereas natural predators often sleep for long periods. Sleep is also

Question 17

What limitations/criticisms of the evolutionary theory of sleep?

Answer 17

> The evolutionary theory assumes that sleep is useful but not essential, and fails to explain the necessity of sleep, regardless of the level of danger and food sources available.

> The theory assumes that sleeping is a way of hiding from predators, while sleeping makes animals more vulnerable due to their loss of awareness during sleep.

Question 18

What is the Restoration Theory of Sleep?

Answer 18

Sleep allows us to recharge our bodies, and to grow and recover from the fatigue of physical and psychological work during the day.

Question 19

What is the biological evidence for the Restoration Theory of Sleep?

Answer 19

The neurotransmitter adenosine (produced when cells use energy) is a cellular waste product that accumulates when we’re awake, making us feel sleepy (as sleep is where we get rid of wastes).

Question 20

What is a hypnogocic state?

Answer 20

Rolling into the first stage of sleep

Question 21

What is the hypnopompic state?

Answer 21

Rolling out of sleep.

Question 22

What limitations/criticisms of for Restoration Theory of Sleep?

Answer 22

> Bedridden people’s sleep patterns are similar to normally active individuals

> Assumes that the body rests during sleep, whilst the brain is active during sleep.

Question 23

What is the ratio of REM to NREM for babies?

Answer 23

50% REM

50% NREM

Question 24

What is the ratio of REM to NREM for teenagers + adults?

Answer 24

20% REM

80% NREM

Question 25

What is the ratio of REM to NREM for elderly?

Answer 25

15% REM

85% NREM

Question 26

What are zietgebers factor?

Answer 26

External or environmental cues that affect the sleep-wake cycle. E.g. level of light in the room

Question 27

What are endogenous factors?

Answer 27

Internal factors that influence the sleep-wake cycle. E.g. low levels of melatonin