Sleep and Circadian Rhythm

Question 1

How does wakefulness differ from REM and non-REM sleep?

Answer 1

Wakefulness:
- aware, active cortex

REM:
- unconscious, active cortex
- skeletal muscle paralysis

Non-REM:
- unconscious, reduced cortical activity
- reduced muscle tone

Question 2

What are the components of polysomnography?

Answer 2

1) Electroencephalogram (EEG)
- brain wave activity

2) Electro-oculogram (EOG)
- eye movements

3) Electromyogram (EMG)
- muscle tone

Question 3

What is the main indication for a clinical sleep study?

Answer 3

Sleep apnea (obstructive)
- additional bio-signals collected:
(airflow sensors, oximetry, nasal pressure, esophageal pressure, body position, respiratory effort, ECG)

Question 4

How do the different sleep stages differ?

Answer 4

Wake with eyes closed:
- α wave predominance
- tonic EMG

N1:
- low voltage theta activity
- slow eye movements
- reduced tone EMG

N2:
- K complexes (high amp, negative wave, followed by slower positive wave) + sleep spindles (12-15Hz bursts >0.5sec)
- no eye movements
- reduced tone EMG

N3: slow wave sleep
- high amp delta activity
- no eyemovements
- reduced tone EMG

REM:
- low voltage mixed freq. waves
- rapid eye movements

Question 5

Of the sleep stages, ___________ is more prominent in the first half of the night, while _______ is more prominent in the latter.

Answer 5

1st 1/2: N3 Slow wave sleep
2nd 1/2: REM

Question 6

How long is 1 REM cycle?

Answer 6

90-120mins
- but varies between and within individuals

Question 7

How does our sleep structure change with age?

Answer 7

Infants have more frequent REM cycles + REM4 (deeper sleep) than older individuals

Question 8

What are the 2 major sleep-promoting processes?

Answer 8

1) Homeostatic sleep drive
- builds with time spent awake

2) Circadian sleep drive
- ↑ during nighttime hours

Question 9

What is an example of a somnogen?

Answer 9

Adenosine

Question 10

What are 3 ways adenosine promotes sleep?

Answer 10

1) Adenosine builds up when energy is used and ATP consumes

2) Excess adenosine non-synaptically released by facilitated transport
- extracellular adenosine is an indicatory of neuronal energy stores

3) Adenosine levels ↑ when awake and ↓ when sleeping in basal forebrain

Question 11

What are 3 neurotransmitters in the arousal system?

Answer 11

1) ACh
- pedunculopontine, dorsolateral tegmental nuclei, basal forebrain

2) NA
- locus coeruleus

3) Serotonin
- raphe nuclei

4) Dopamine
- ventral tegmental area

5) Histamine
- tuberomammillary nucleus

6) Orexin
- lateral hypothalamus

Question 12

How does the ventrolateral preoptic nucleus promote sleep?

Answer 12

GABAergic → inhibit arousal system
- activated by prostaglandin D2 (somnogen)

Question 13

Which type of neurons are active during REM sleep?

Answer 13

1) GABA (inhibit arousal)
2) ACh (cortical activity)

Question 14

Which chemical stabilises sleep-wake transition?

Answer 14

Orexin
- activated arousal system
- inhibited by VLPO (GABA)

Question 15

How do the sleep cycles of narcolepsy differ from normal individual?

Answer 15

1) More sleep-wake transitions vs normal subject

2) Direct entry into REM sleep from wakefulness (skip N1-3)

3) Multiple sleep bouts/attacks during daytime

Question 16

Which part of the brain controls the circadian rhythm?

Answer 16

Suprachiasmatic nucleus

Question 17

What is the physiology of blue light therapy in treating circadian misalignment?

Answer 17

Blue-light sensitive melanopsin in retinal ganglion cells → SCN → light induced resetting of circadian rhythm

Question 18

What are the 2 chronotypes?

Answer 18

1) Morningness
- shorter-than-average circadian period

2) Eveningness
- longer-than-average circadian period

Question 19

What is insomnia?

Answer 19

difficulty falling asleep or maintaining sleep across the night

Question 20

What is obstructive sleep apnea?

Answer 20

excessive daytime sleepiness due to repeated obstruction of the airway during sleep
- fragmented sleep and ↓ slow-wave sleep
- During sleep, muscle tone is reduced including the upper motor airway

Question 21

Obstructive sleep apnea
- causes (1)
- indicator (1)
- sequelae (3)

Answer 21

Causes: obesity
Indicator: chronic snoring
Sequelae:
- Hypoxemia
- HTN
- IHD
- excessive daytime sleepiness

Question 22

What are 2 movement disorders of sleep?

Answer 22

1) Periodic limb movement disorder
- excessive leg movements during sleep
- can wake person

2) Restless legs syndrome
- uncomfortable sensations in legs relieved by stretch/rubbing
- Diagnostic criteria:
1) Urges to move the legs, accompanied or caused by uncomfortable and unpleasant sensations in the legs
2) a worsening of symptoms during periods of rest or inactivity
3) the unpleasant sensations are partially or totally relieved by movement (e.g., walking or stretching)
4) the symptoms are worse in the evening or at night compared to the daytime.

Question 23

What is cataplexy?

Answer 23

Sudden loss of muscle tone while awake, often caused by emotion
- symptom of narcolepsy

Question 24

What are 4 symptoms of narcolepsy?

Answer 24

1) excessive daytime sleepiness
2) cataplexy
3) sleep paralysis
4) hypnagogic hallucinations

Question 25

What is 1 cause of narcolepsy?

Answer 25

Loss of orexin neurons

Question 26

What is delayed sleep-wake phase disorder?

Answer 26

Sleep onset insomnia and extreme difficulty waking in the morning