Biological Processes of sleep

Question 1

The role of the brain in sleep

Endogenous pacemaker

Answer 1

The internal biological clock. The sleep-wake cycle is controlled by a small area of the hypothalamus called the SCN. The electrical activity of the SCN has an endogenous (built in) circadian rhythm.

Question 2

The role of the brain in sleep

Endogenous pacemaker (evidence - Michel Siffre)

Answer 2

Michel Siffre
- lived in total isolation for two months in 1962
- no clocks or daylight to mark times
- phoned his researchers every time he woke up, ate and went to sleep
- had erratic sleep patterns
- sleep-wake cycle of 24-25 hours

Question 3

The role of the brain in sleep

Endogenous pacemaker
(evidence - Stephan & Zucker)

Answer 3

1972
- laboratory rats
- 12 hours of light and 12 hours of darkness
- circadian rhythm became more active and drinking more during the dark period of time
- when SCN was damaged, circadian rhythm changed/stopped
- concluded that SCN was the key pacemaker

Question 4

The role of the brain in sleep

Exogenous pacemakers

Answer 4

the external cues from the environment i.e light. The retina of the eye is connected to the SCN via a nerve pathway. Therefore light also affects the SCN and the pineal gland.

Light is an exogenous pacemaker

Question 5

The role of the brain in sleep

Endogenous sleep regulating substances

Answer 5

Adenosine builds up in our cerebrospinal fluid during our waking hours which has the effect of the increasing the pressure to sleep the more it accumulates.

Adenosine inhibits some neurotransmitters associated with wakefulness for e.g. serotonin.

Question 6

The role of the brain in sleep

Endogenous sleep regulating substances (research)

Answer 6

Experiments have clearly shown that high levels of adenosine lead to sleepiness.

Studies in animals have shown that blocking adenosine’s actions in the brain increases alertness while injections of adenosine or similar compounds induce sleep.

Question 7

The role of the brain in sleep

Endogenous sleep regulating substances (evidence - caffeine)

Answer 7

Caffeine which is a common stimulant acts by blocking the effects of adenosine

Question 8

The role of the brain in sleep

The pineal gland

Answer 8

The SCN sends regular daily impulses via nerves to the pineal gland to produce the hormone melatonin (the sleep hormone - high levels stimulate sleep).

Question 9

The role of the brain on sleep

Melatonin

Answer 9

• is released when it gets dark
• released in the bloodstream in the evening
• makes us feel sleepy and eventually falls asleep
• levels peak in the middle of the night

Question 10

The role of the brain in sleep

The sleep-wake cycle

Answer 10

an example of a homeostatic mechanism.
- the longer we have been awake, the greater the likelihood of falling asleep
- the longer we have been asleep, the more the pressure to sleep dissipates and the greater the likelihood of awakening

Question 11

Circadian rhythm

Answer 11

• a body rhythm that cycles over 24 hours
• used to anticipate the differing demands of the 24-hour day

Question 12

Circadian rhythm

What controls our circadian rhythm?

Answer 12

Our circadian rhythms are controlled by the hypothalamus which is an area of our brain in charge of keeping our bodies in a balanced state called homeostasis.

Question 13

Circadian rhythm

What controls our sleep-wake cycle?

Answer 13

Our sleep-wake cycle is controlled by an area of the hypothalamus called the SCN. The SCN communicates with the pineal gland which releases melatonin.

Question 14

Circadian rhythm (body changes)

Answer 14

• body temperature drops
• blood pressure decreases
• cognitive performance declines
• tiredness increases

Before dawn, metabolism is geared up in anticipation of increased activity when we wake.

Question 15

Circadian rhythm

Shift work

Answer 15

can disrupt biological rhythm

i.e when people work throughout the night and sleep during the day
- can result in CRSDs

Question 16

Circadian rhythms

Shift work (explained further)

Answer 16

shift work upsets our natural biological rhythm as employees are required to work when they should be asleep vice versa.

Shift work usually rotate through different shifts (midnight to 8am, 8am-4pm, 4pm to midnight)
- further upsets the biological clock and like jet lag requires some time to readjust.

Question 17

non-REM and REM sleep and dreaming

EEG - electroencephalograph

Answer 17

• allows scientists to examine the brain while awake and while sleeping.
• records the activity of the brain by placing electrodes onto the skull which detect electrical activity.

Question 18

non-REM and REM

stages of sleep (process/cycle)

Answer 18

Sleep begins in stage 1 and progresses into stages 2, 3 and 4. After stage 4 sleep, stage 3 and then stage 2 sleep are repeated before entering rapid eye movement (REM) sleep. Once REM sleep is over, the body usually returns to stage 2 sleep. Sleep cycles through these stages approximately four or five times throughout the night.

On average, we enter the REM stage approximately 90 minutes after falling asleep. The first cycle of REM sleep might last only a short amount of time, but each cycle becomes longer. REM sleep can last up to an hour.

Question 19

non-REM and REM sleep

REM sleep and EEG activity

Answer 19

After a person progresses through the first four stages of SWS, they enter a mysterious fifth stage callled REM sleep which sits between being awake and SWS stage 1.

EEG activity suddenly increases, mimicking the fast, desynchronised activity of an awake person and heart rate increases.

Question 20

non-REM and REM sleep

paradoxical sleep and sleep paralysis

Answer 20

The person is actually in the deepest form of sleep. They are almost impossible to wake and their muscles are so relaxed they are essentially paralysed.

Question 21

Oswald’s (1966) restoration theory of sleep

(1, 2, 3)

Answer 21

1. the need to breakdown an unwanted substance which accumulates in the body during activity
2. the need to carry out some essential process of chemical synthesis, which is inefficient or impossible during wakefulness
3. body restoration occurs during deep sleep and that the brain restoration process occurs during REM sleep, partially through stimulating neural protein synthesis

Question 22

Oswald’s restoration theory of sleep

… proposed that …

Answer 22

• REM sleep restores the brain
• non-REM sleep restores the body

Question 23

Oswald’s restoration theory of sleep

Evidence - Shapiro et al (1981)
contradicting evidence - Horne and Harley (1988)

Answer 23

• studied ultra-marathon runners
• after they had slept for longer (non-REM sleep increased particularly)
• warming of the brain during exercise that led to increased sleep in Shapiro’s study
• to test, he heated people’s faces and heads with a hairdryer
• majority of the participants did go on to have a longer period of time in non-REM sleep

Question 24

Oswald’s restoration theory of sleep

Evidence - Rechtschaffen (1983)
contradicting evidence - dolphins and seals

Answer 24

• prolonged sleep deprivation in rats caused metabolic rate, loss of weight and die after a couple of weeks
• if they slept during this time, they did not die.
• shows the importance of sleep for survival
• many animals such as dolphins and seals have very little REM sleep with no adverse effects.

Question 25

Oswald's restoration theory of sleep Evidence - fatal familial insomnia

Answer 25

- sleep normally until middle age when they simply stop sleeping - leading to death within a couple years - cases are very rare - support the idea that sleep is needed to restore the body - sample size is so small - difficult to generalise

Question 26

Cortisol

Answer 26

Cortisol is comonly known as the stress hormone: it controls our flight-or-fight response if we identify a stressor.

Question 27

Cortisol In reference to sleep-wake cycle

Answer 27

To help regulate the sleep-wake cycle. Cortisol levels rise and fall throughout a 24-hour period which helps us to fall asleep, stay asleep and wake up.