Chapter 8: Wakefulness & Sleep

Question 1

What is the purpose of the biological clock?

Answer 1

To keep our internal workings in phase with the outside world

Question 2

What stimulus resets the biological clock?

Answer 2

Referred to as “zeitgeber” meaning “time-giver” which refers to the stimulus that resets the circadian rhythm

Question 3

What are some examples of disruptions to the circadian rhythm?

Answer 3

Jet lag- distruption due to crossing time zones (most people find it easier to adjust to crossing time zones going West than East). Cortisol (adrenal hormone) elevates during the adjustment to jet lag and may damage neurons in the hippocampus
Shift work - due to irregular sleeping patterns
Morning people/evening people -adjusting to circadian rhythms differ amongst people and age plays a factor.

Question 4

Who introduced the concept of the biological clock and what are the mechanisms behind it?

Answer 4

Curt Richter (1967) - the brain generates its own rhythms aka the “biological clock” and is insensitive to most interference. The Suprachiasmatic Nucelus (SCN), genes that produce certain proteins (biochemistry) and melatonin levels

Question 5

What are circadian and circannual rhythms ?

Answer 5

Circannual - rhythm that prepares an animal for seasonal changes eg birds fly north due to change in temperature and amount of daylight available
Circadian - rhythm that operates on a 24 hour cycle

Question 6

What are the basic principles of the SCN and how does light reset the SCN?

Answer 6

It is part of the hypothalamus and is located above the optic chiasm. It is the main control centre of the circadian rhythms of sleep and temperature. Damage to the SCN results in erratic behaviour e.g. researchers found that a mutation in one gene causes hamster’s SCN to produce a 20-hour instead of 24-hour cycle.
Light resets the SCN via the retinhypothalamic path from a small branch of the optic nerve. The retinohypothalamic path come from ganglion cells containing a photo pigment melanopsin in which the cells respond directly light do not require input from rods or cones.

Question 7

Which genes are responsible for generating the circadian rhythm?

Answer 7

Period (PER) and timeless (TIM) produce the proteins PER and TIM. (Review page 269)

Question 8

What is the relationship between melatonin and the SCN?

Answer 8

The SCN regulates the pineal gland, an endocrine gland located posterior to the thalamus. The pineal gland secretes melatonin, a hormone that increases sleepiness, therefore influencing both circadian and circannual rhythms.

Question 9

What is sleep?

Answer 9

Sleep is a state that the brain actively produces and is characterised by a decreased response in stimuli. Sleep differs from other unconscious states such as coma, vegetative state and brain death.

Question 10

How are the stages of sleep measured?

Answer 10

Through EEG (electroencephalograph) which records an average of the electrical potentials of the cells and fibres in the brain areas.

Question 11

What are the characteristics of Stage 1 sleep?

Answer 11

This stage is when sleep has just begun and the EEG is dominated by irregular, low voltage waves. Brain activity also begins to decline at this stage

Question 12

What are the characteristics of Stage 2 sleep?

Answer 12

Sleep spindles (12-14Hz waves during a burst that lasts at least half a second) and K-complex (sharp wave associated with temporary inhibition of neuronal firing) are present during stage 2.

Question 13

What are the characteristics of stages 3 & 4 sleep?

Answer 13

They both constitute slow-wave sleep (sws) and is characterised by slow amplitude waves, slowing of heart rate, breathing, brain activity. Also characterised by highly synchronised neuronal activity.

Question 14

What are the characteristics of Paradoxical (REM) sleep? What is the additional stage to REM sleep?

Answer 14

It is a deep sleep and involves periods of rapid eye movement (REM). The EEG shows irregular, low-voltage, fast waves which indicate increased neuronal activity.
non-REM (NREM) is known as the stages of sleep which are not known as REM (review page 274).

Question 15

Review the sections on brain mechanisms

Answer 15

Review page 275, 276, 277

Question 16

Which brain areas are involved in REM sleep?

Answer 16

Activity is increased in the pons (which triggers the onset of REM) and in the limbic system (which is important for emotional response). Activity is decreased in the primary visual cortex , the motor cortex, dorsolateral prefrontal cortex but increased in parts of the parietal and temporal cortex.

Question 17

Give some examples of sleep disorders

Answer 17

Sleep apnea - inability to breathe whilst sleeping, Narcolepsy - characterised by frequent periods of sleepiness during the day, Periodic limb movement disorder - frequent involuntary movement of the legs (and arms) during sleep

Question 18

What is the activation-synthesis hypothesis?

Answer 18

It is a biological perspective to dreaming that represents the brain’s effort to make sense of distorted information that originates within the pons. A criticism of this theory is that its predictions are vague.

Question 19

What is the clinic-Anatomical Hypothesis?

Answer 19

It is a biological perspective to dreaming that was derived from clinical studies of patients with varying forms of brain damage. This theory emphasises that dreams begin with arousing stimuli that are generated within the brain in conjunction to recent memories and information. However, this theory puts less emphasis on the PGO waves, pons and REM sleep. This theory regards dreams as thinking that takes place under unusual conditions.