Chapter 9: Sleep Part 1

Question 1

What is sleep defined as?

Answer 1

A reversible behavioural state of perceptual disengagement and unresponsiveness to the environment.

Question 2

List the 3 characteristics which distinguish sleep from other ASCs:

Answer 2

• Reversibility
• Perceptual disengagement
• Unresponsiveness

Question 3

Describe reversibility in relation to sleep and give an example:

Answer 3

Individuals can always be awoken with a strong enough stimulus.
Eg. A loud noise or someone shaking you.

Question 4

Describe perceptual disengagement in relation to sleep and give an example:

Answer 4

Individuals have no awareness of sensory stimuli when asleep.
Eg. Sights, sounds, and smells.

Question 5

Describe unresponsiveness in relation to sleep and give an example:

Answer 5

Individuals are unresponsive to environmental stimuli, however, a strong enough stimulus may wake the sleeper but their perception of the stimulus will be different to when they are awake.
Eg. Sleepwalking and talking.

Question 6

What are biological rhythms? Give some examples:

Answer 6

Cyclic changes in bodily functions or activities that repeat themselves through time in the same order.
-Are coordinated by the brain and are synchronised to influence what time we are most alert, hungry, tired, or physically primed.
Eg. Body temperature, blood pressure, blood sugar, secretion of hormones, sleep-wake cycle.

Question 7

What are circadian rhythms and where does the term come from? Give an example:

Answer 7

Biological rhythms that involve changes in bodily functions or activities that occur as part of a cycle with a duration of about 24 hours.
-Term circadian comes from the Latin words circa dies (about one day)
Eg. Sleep-wake cycle

Question 8

What are zeitgebers and what is meant by the term entrained? Give an example:

Answer 8

Environmental cues that help to maintain the biological clock to a 24-hour day.
-When a clock is reset and matched to an environmental cycle or changes due to the influence of a zeitgeber, it is said to be entrained.
Eg. Our circadian rhythms are typically entrained to the daily day-night cycle of our external environment.

Question 9

Describe how light is the main environmental cue that influences the sleep-wake cycle:

Answer 9

• The SCN receives info about the amount of incoming light from the eyes and adjusts the sleep-wake cycle,
• Neuronal messages are sent to the nearby pineal gland to secrete more or less of the hormone into the blood.
• The amount of melatonin in the blood is linked to alertness.
• Higher melatonin is associated with greater drowsiness and vice versa.
• When there is less light (eg. after sunset) the SCN signals to the pineal gland to produce and secrete more melatonin - we become more drowsy and sleep is induced.
• Melatonin levels stay high during the night and fall back to low daytime levels before daylight.

Question 10

What is the suprachiasmatic nucleus (SCN) and where is it located?

Answer 10

An area of the hypothalamus that regulates the timing and activity of the sleep-wake cycle.
-Located just above the optic chiasm, the point where the optic nerves that connect the eyes and brain cross.

Question 11

What is an ultradian rhythm? Give an example:

Answer 11

A biological rhythm that involves changes in bodily functions or activities that occur as part of a cycle shorter than 24 hours.
Eg. Our eating behaviour

Question 12

Describe NREM sleep:

Answer 12

Non-Rapid Eye Movement:

• Has 4 stages, where each successive stage is indicative of a deeper sleep
• Makes up 75-80% of our total sleep time
• We transition back again from deep sleep in stage 4

Question 13

Describe stage 1 of NREM sleep:

Answer 13

• Drift into and out of a true sleep state as we gradually lose awareness
• Makes up 4-5% of our total sleep time
• Low arousal threshold

Question 14

Describe stage 2 of NREM sleep:

Answer 14

• Period of light sleep
• Requires more intense stimuli than in stage 1 to awaken
• Midway through stage 2, we are unlikely to respond to anything except extremely strong or loud stimuli
• In the first cycle, this stage lasts for about 10-15 mins and lengthens with each successive cycle, eventually making up about 45-55% of our total sleep time

Question 15

Describe stage 3 of NREM sleep:

Answer 15

• Moderately deep sleep
• Transitionary stage between shallow sleep of stage 2 and the deep sleep of stage 4
• Typically last for a few minutes up to 10 mins
• Makes up about 3-8% of our total sleep time
• In sleep cycles in the latter half or so of a sleep episode there may be no stage 3 sleep at all
• Become less and less responsive to external stimuli

Question 16

Describe stage 4 of NREM sleep:

Answer 16

• As the night progresses, less and less time is spent in stage 4 and the stage may disappear altogether
• Stage 4 make up 10-15% of our total sleep time
• Stages 3&4 are now commonly combined and described as one stage

Question 17

What is a hypnogram?

Answer 17

A sleep graph

Question 18

Describe REM sleep:

Answer 18

Rapid Eye Movement:

• About 20-25% of our total sleep time is spent in REM
• The body’s internal functioning is more active during REM sleep than during NREM
• Most dreaming occurs during REM
• Some psychologists have proposed that sleep paralyis may serve an important role in preventing individuals from ‘acting out’ their dreams or nightmares while sleeping
• REM sleep periods lengthen and occur closer together as a sleep episode progresses
• REM sleep shares properties of both light and deep sleep

Question 19

Why is REM sleep also called paradoxical sleep?

Answer 19

Because internally the brain and body are active, while externally the body appears calm and inactive.

Question 20

What does the restoration theory propose?

Answer 20

Proposes that sleep provides ‘time out’ to help us recover from depleting activities during waking time that use up the body’s physical and mental resources.

Question 21

What is the function of sleep according to the restoration theory? Give some examples:

Answer 21

Sleep provides an opportunity for the body to recover by replenishing resources that have been used up during the day.
Eg. Damaged cells are repaired, muscles are detoxified.

Question 22

Give an example of research that supports the restoration theory:

Answer 22

For most of the time when we are asleep, our muscles are relaxed, body functions such as heart and breathing rates slow down, and the rate of neural activity in various brain structures is slightly reduced.

Question 23

Describe the restorative functions of NREM sleep in relation to the restoration theory:

Answer 23

-Generally, NREM sleep is considered to be important for restoring and repairing the body
Eg. Physical growth, tissue repair, and recovery from the effects of fatigue may occur during NREM sleep.

Question 24

Describe the restorative functions of REM sleep in relation to the restoration theory:

Answer 24

• REM sleep is much more abundant in the developing fetus and infant than in any other lifespan stage, indicating that it is essential to brain development
• REM sleep promotes the maintenance of neural pathways
• May assist in the consolidation of new memories

Question 25

What does REM rebound involve?

Answer 25

Involves catching up on REM sleep immediately following a period of lost REM sleep by spending more time than usual in REM sleep when we next sleep.