Sleep

Question 1

What three techniques are used to monitor activity during sleep?

Answer 1

Electroencephalography (EEG)

Electromyography (EMG)

Electrooculography (EOG)

Question 2

Describe the EEG and EMG activity in wakefulness.

Answer 2

EEG – fast brain rhythm – beta waves (13–>~30 Hz)

EMG – reasonable amount of muscle tone because you are maintaining posture and ready for action

Question 3

Describe the EEG, EMG and EOG activity in non-REM sleep (stages 1-4).

Answer 3

Stage 1+2
 Light sleep
 EEG – beta–>theta (4-8 Hz) waves – gradually becoming more and more drowsy
 EOG – NO eye movements
 EMG – muscle activity reduced considerably

Stage 3+4 
 Very deep sleep
 EEG - Delta activity (< 4 Hz)
 EOG – MINIMAL eye movement
 EMG – continued relaxation of muscles

Question 4

Describe the EEG, EMG and EOG activity in REM sleep.

Answer 4

EEG – brain shifts abruptly back to fast rhythm (similar to wakefulness)
EOG – rapid eye movement
EMG – muscle activity at its lowest – subject is basically paralysed

Question 5

How long is a normal sleep cycle?

Answer 5

1-1.5 hours (60-90 mins)

Question 6

Compare the relative amounts of NREM and REM sleep in a sleep cycle at the start of a night’s sleep and at the end.

Answer 6

Start of the night – more NREM sleep

End of the night – more REM sleep, plus less/no stage IV

Question 7

Describe how heart rate and respiratory rate change during sleep.

Answer 7

SLOW during NREM

FAST during REM sleep

Question 8

Which system is responsible for maintaining consciousness?

Answer 8

Reticular activating system

Question 9

How does the reticular activating system control the activity of the cortex?

Answer 9

Either via direct connections

Or via indirect connections through the intralaminar nuclei of the thalamus

Question 10

What are the two important nuclei in the hypothalamus that are responsible for influencing the reticular activating system and, hence, regulating the sleep-wake cycle?

Answer 10

Lateral Hypothalamus (LH) – excitatory- promotes wakefulness

Ventrolateral Preoptic Nucleus (VLP) – inhibitory-promotes sleep

NOTE: they have an antagonistic relationship

Question 11

Describe the circadian synchronisation of the sleep-wake cycle.

Answer 11

The suprachiasmatic nucleus is responsible for synchronising the sleep-wake cycle with falling light level

It receives an input from the retina (not from the usual photogenic cells)

As light level falls the suprachiasmatic nucleus becomes more active- activates more nuclei within hypothalamus

Question 12

Describe the effect of the suprachiasmatic nucleus on the nuclei within the hypothalamus.

Answer 12

Falling light level –> increased activity of suprachiasmatic nucleus

This leads to activation of ventrolateral preoptic (VLP-inhibitory) nucleus and inhibition of lateral hypothalamus (LH-excitatory) so you become sleepier

Also has direct effects on RAS

Question 13

What other important projection does the suprachiasmatic nucleus have and what is the importance of this projection?

Answer 13

Projection to the pineal gland

Increase in suprachiasmatic nucleus activity leads to activation of pineal gland so that it releases melatonin

Melatonin adjusts various physiological processes in the body that fit with sleep

Question 14

What are some consequences of sleep deprivation?

Answer 14

Sleepiness/irritability

Performance decrements

Concentration difficulties

Glucose intolerance – risk of diabetes

Reduced leptin

Hallucinations

Question 15

Describe three ways in which sleep is regulated after sleep deprivation.

Answer 15

Reduced latency of sleep onset (fall asleep faster)

Increased NREM sleep (sleep for longer)

Increased REM sleep (after selective REM sleep deprivation)

Question 16

During what stages of sleep can you dream?

Answer 16

Both NREM and REM but you tend to dream more and are able to recall dreams better during REM sleep

Question 17

Describe the brain activity of the limbic system compared to the frontal lobe in sleep.

Answer 17

Brain activity in the limbic system is higher than in the frontal lobe

This is because the content of dreams tends to be more emotional than in real life

Question 18

Sleep is important in memory consolidation. What is the difference in memory consolidation between NREM and REM sleep?

Answer 18

NREM – declarative = facts and events

REM – procedural = learning skills

Question 19

State some causes of insomnia that are physiological or due to brain dysfunction.

Answer 19

Physiological – sleep apnoea, chronic pain

Brain Dysfunction – depression, fatal familial insomnia, night work

Question 20

Hypnotics can be used to treat insomnia. How do they work?

Answer 20

They enhance the inhibitory (GABAergic) circuits in the brain

Question 21

What is narcolepsy?

Answer 21

A condition characterised by an extreme tendency to fall asleep whenever in relaxing surroundings

Question 22

What is cataplexy?

Answer 22

Sudden onset of muscle weakness that may be precipitated by excitement or emotion

Question 23

Explain cataplexy with regards to the sleep cycle.

Answer 23

It tends to be due to a dysfunction of control of REM sleep

Patients go straight to REM sleep without going through NREM sleep so they become paralysed

Question 24

What is narcolepsy caused by?

Answer 24

Orexin deficiency

Orexin is a neuropeptide, which is the neurotransmitter in the lateral hypothalamus

Orexin deficiency could be autoimmune or genetic

Manage with tight control of sleep

Question 25

What are the potential consequences of working night shifts?

Answer 25

Physiological processes could become desynchronised

This can lead to sleep disorders, fatigue and increased risk of some conditions such as obesity, diabetes and cancer