Lecture 7 - Sleep

Question 1

What are circannual rhythms?

Answer 1

behaviours that repeat yearly e.g. hibernation

Question 2

What are circadian rhythms?

Answer 2

behaviours that repeat daily + follow a 24 hour cycle e.g. sleep/ wake cycle

Question 3

What are ultradian rhythms?

Answer 3

behaviours that are repeated within 24 hours e.g. sleep stages, heart rate

Question 4

What are zeitgebers?

Answer 4

• environmental events that entrain biological rhythms
• the main Zeitgeber for the circadian rhythm is light

Question 5

Do we have a biological clock?

Answer 5

• research has shown that humans have a daily rhythm of waking and sleeping without cues about day and night
• humans have a biological clock that governs the sleep-wake cycle
• biological clocks can be reset each day so that they correspond to the season

Question 6

The neural basis of a biological clock?

Answer 6

• the SCN = an endogenous circadian clock
• the SCN receives a direct input from the retina allowing light to direct the rhythmic activity of the SCN via the retinohypothalamic pathway

Question 7

Transplants that prove the SCN controls the circadian rhythm?

Answer 7

• in an experiment the circadian rhythms of hamsters with a lesioned SCN were observed
• they displayed chaotic rhythmic behaviours
• however if the SCN from another animal was transplanted then a normal circadian rhythm was observed

Question 8

Melatonin and the biological clock?

Answer 8

• during the dark phase of the sleep/wake cycle the pineal gland secretes melatonin
• light inhibits the secretion of melatonin
• melatonin acts on receptors of the SCN to affect the circadian rhythm

Question 9

Seasonal affective disorder (SAD)?

Answer 9

• the importance of light in entraining circadian rhythms is explained in SAD
• during the winter months 60% of people report depression
• one explanation of SAD is that the lack of light signals hibernation
• the disruption of the circadian rhythm can be prevented by sitting in front of a bank of bright lights for 20 minutes a day

Question 10

What are brain waves like during sleep?

Answer 10

• when awake the pattern of activity = low amplitude, high frequency
• as the person goes into a deeper sleep the pattern changes to high amplitude, low frequency
• however this pattern can be interrupted by bursts of REM sleep = low amplitude, high frequency

Question 11

What happens during non REM sleep?

Answer 11

• body temp declines, heart rate decreases and levels of growth hormone increase
• sleep walking is thought to occur during NREM sleep
• insomnia and sleep apnea are disorders to NREM sleep

Question 12

What happens during REM sleep?

Answer 12

• body temp increases
• if we wake-up during REM sleep we are more likely to report that we have been dreaming, waking up in non-rem means dreams are less easy to remember

Question 13

What are the disorders of REM sleep?

Answer 13

1. sleep paralysis
2. narcolepsy
3. cataplexy

Question 14

What are the 3 biological functions of sleep?

Answer 14

1. biological adaptation
2. body restoration
3. memory consolidation

Question 15

What are the 2 biological adaptations of sleep?

Answer 15

1. energy conservation
2. predator avoidance

Question 16

Energy conservation?

Answer 16

• sleep is an energy conserving strategy
• species gather food at optimal times and conserve energy the rest of the time

Question 17

Predator avoidance?

Answer 17

• amount of sleep is influenced by whether an animal is a predator or prey
• if an animal is a predator it can sleep at ease but if its prey its sleep is reduced because it must remain alert

Question 18

Sleep as a restorative process?

Answer 18

• based on the idea we require sleep to rejuvenate our body
• only weakly supported by evidence - energetic activity prior to sleep encourages us to sleep earlier but not sleep longer

Question 19

What part of the brain puts us to sleep?

Answer 19

• The preoptic area in hypothalamus promotes sleep via the action of melatonin
• Hypothalamus slows down the firing rate of the thalamus via the brainstem
• Thalamus is the sensory relay station – slow firing means sensory information flow to the cortex is slowed down
• The neurotransmitter that mediates this overall slowing down of brain activity is GABA

Question 20

Wakefulness and the ascending reticular activating system?

Answer 20

• The posterior hypothalamus promotes wakefulness through the Reticular Activating System of the brainstem
• The neurotransmitters that regulate this are:
  -> Noradrenaline from the locus coeruleus
  -> Serotonin from the raphe nucleus
  -> Acetylcholine from the brainstem & forebrain
• With hypothalamus and brainstem waking up, thalamus sends more sensory information to the cortex.
• Damage to the RAS = coma

Question 21

Neuronal control of sleep?

Answer 21

• Neurons that control sleeping are part of our regulatory neurotransmitter system
• NE, serotonin and ACh neurons fire during waking and enhance the awake state
• ACh also enhances critical REM events
• Metabolic activity during awake times, increase adenosine which promotes sleep by inhibiting excitatory neurotransmitters
• Regulatory systems control the rhythmic behaviour of the thalamus which controls the EEG rhythms of the cortex
• Slow rhythms block the flow of sensory information to the cortex
• Descending activity is required to inhibit motor neurons during dreaming

Question 22

Mechanisms of REM sleep?

Answer 22

• Control of REM sleep comes from regulation in the brain stem, at the pons
• Firing rates of the locus corerulus and raphae nuclei decrease to nothing
• Ach neurons in the pons increase firing