Lesson 2

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Questions and Answers

What aspect of sleep is primarily influenced by Process S?

Daytime alertness

Duration of REM sleep

Circadian timing

NREM sleep prioritization (correct)

How does sleep deprivation affect the subsequent sleep cycle?

Does not affect sleep duration

Increases sleep pressure leading to longer NREM (correct)

Increases REM sleep only

Reduces total sleep time

What is the role of the SCN in sleep regulation?

Controls sleep medications timing

Influences the severity of sleep deprivation

Regulates only NREM sleep

Governors circadian processes related to alertness (correct)

Which statement about cancer treatments and timing is accurate?

Certain times of day enhance their effectiveness and reduce toxicity Signup and view all the answers

What describes the relationship between Process C and REM sleep?

REM sleep is more influenced by Process C but is still affected by homeostasis Signup and view all the answers

What characterizes Rem sleep paralysis?

Inhibits all nerve connections to skeletal muscles Signup and view all the answers

Which component of polysomnography primarily measures eye movement?

Electrooculography (EOG) Signup and view all the answers

What is the primary aim of circadian rhythms in organisms?

To synchronize bodily functions with environmental changes Signup and view all the answers

What is the typical duration of one complete sleep cycle in humans?

90 minutes Signup and view all the answers

What type of sleep is characterized by high amplitude and low frequency brain waves?

Slow-wave sleep (Stage 3 and 4 NREM) Signup and view all the answers

Which stage of NREM sleep is primarily associated with memory consolidation?

Stage 2 NREM Signup and view all the answers

What phenomenon occurs when the body fails to transition smoothly through sleep phases?

Circadian disruption Signup and view all the answers

Which of the following is NOT a characteristic of awake brain activity?

Muscle atonia Signup and view all the answers

What factors can serve as Zeitgebers for regulating circadian rhythms?

Light exposure and meal times Signup and view all the answers

What distinguishes phasic REM sleep from tonic REM sleep?

Presence or absence of rapid eye movements Signup and view all the answers

What is a factor that can contribute to jet lag?

Circadian disruption due to rapid time zone changes Signup and view all the answers

What type of biological rhythm occurs faster than a 24-hour cycle?

Ultradian rhythm Signup and view all the answers

Why do younger individuals exhibit larger amplitude slow waves during sleep compared to older adults?

Changes in neurological health with age Signup and view all the answers

What is the significance of the hypnogram in sleep studies?

It depicts the transition between different sleep stages Signup and view all the answers

Study Notes

Sleep Measurement

Phenomenology: Subjective experience of sleep, including loss of external awareness, disconnected thoughts, and disorientation in time and space.
Behavior: Observable characteristics of sleep such as horizontal body position, low muscle tone, and responsiveness to stimuli.
Physiology: "Gold standard" for measuring sleep using polysomnography (PSG).

Polysomnography (PSG)

Electroencephalography (EEG): Measures electrical activity of the brain through electrodes placed on the scalp.
- Brain waves: Reflect different stages of sleep.
Electrooculography (EOG): Records eye movements by monitoring electrical activity near the eye.
- Eye movements: Indicate specific sleep stages, particularly REM sleep.
Electromyography (EMG): Measures muscle activity using electrodes placed under the chin and on the face.
- Muscle tension: Represents changes in muscle tone throughout sleep.

Types of Sleep - Sleep Stages

Non-Rapid Eye Movement (NREM) Sleep: Increases in depth across stages 1 through 4.
- Stage 1: Transitional stage characterized by slower brain waves.
- Stage 2: Deeper sleep, characterized by sleep spindles and K-complexes.
- Slow-Wave Sleep (SWS): Stages 3 and 4, marked by very slow brain waves (delta waves).
Rapid Eye Movement (REM) Sleep: Characterized by rapid eye movements, PGO waves, and dream sleep.
- REM Sleep Paralysis: Muscles become inhibited, preventing movement during dreams.

Sleep Cycle

Hypnogram: Diagram showcasing the architecture of sleep.
NREM/REM Cycle: Approximately 90 minutes in humans.
Early sleep: Dominated by deep NREM (slow wave sleep)
Later sleep: Dominated by more REM sleep.

Appearance of Sleep Stages

Awake:
- Eyes: Open with blinks.
- Brain waves: High frequency, low amplitude, desynchronized.
- Muscle: Strong muscle tone.
Stage 1 NREM:
- Eyes: Slow, rolling eye movements.
- Brain Waves: Slower frequency, higher amplitude, more synchronous.
- Muscle: Lowered muscle tone.
Stage 2 NREM:
- Eyes: Eye movements stop.
- Brain Waves: Slower frequency, higher amplitude, more synchronized.
- Muscle: Lowered muscle tone.
- Special events: K-complexes and sleep spindles.
Stage 3 + 4 NREM (Slow Wave Sleep):
- Eyes: No identifiable eye movements.
- Brain Waves: Very slow frequency, high amplitude, synchronized.
- Muscle: Limited muscle tone.
REM Sleep:
- Eyes: Closed, but rapid, horizontal eye movements.
- Brain Waves: High frequency, low amplitude, desynchronized.
- Muscle: Atonia (no muscle tone).

Discussion 1: Polysomnography in Practice

Polysomnography (PSG): Simultaneous recording of (EEG), (EOG), and (EMG).
X-axis: Time.
Y-axis: Amplitude.
Power: Amplitude integrated across time.
Stage 4 SWS sleep: Channels show synchronized delta waves in parallel, indicating synchronous brain activity.
REM Sleep:
- Phasic REM: Frequent bursts of rapid eye movements.
- Tonic REM: No eye movements.
- EEG shows high frequency, low amplitude, desynchronized activity, similar to wakefulness.
- EMG shows extremely low muscle activity.

Circadian Rhythms

Circadian rhythms: Biological rhythms that occur in 24-hour cycles.
Diurnal: Active during the day and sleep at night.
Nocturnal: Active during the night and sleep during the day.
Crepuscular: Active during twilight.
Ultradian: Cycles faster than 24 hours (e.g., cycles within the sleep cycle).
Infradian: Cycles slower than 24 hours (e.g., menstrual cycle).

Entrainment and Zeitgebers

Zeitgebers: External cues that synchronize circadian rhythms.
- Light: Primary zeitgeber.
- Food: Important for peripheral clocks in the liver and pancreas.
- Exercise and Activity: Can help strengthen circadian rhythm, particularly in older adults.
Melatonin: Hormone that can phase-advance the internal clock.
Jet Lag: Disruption of circadian rhythm caused by travel across multiple time zones.

Circadian Disruption and Health Implications

Cognitive Deficits: Shift work and jet lag can lead to decreased cognitive function.
Increased Cortisol Levels: Can be caused by chronic circadian disruption.
Increased Cancer Risk: Sleep deprivation is linked to cancer risk.
Blood pressure medications: Most effective when taken at specific times of day.
Cancer Treatments: Some cancer drugs are more effective and less toxic at certain times of day.

Two-Process Model of Sleep Regulation

Process S (Homeostatic Sleep Drive): Represents sleep debt. Increases during wakefulness and decreases during sleep.
- Adenosine: Neurochemical associated with Process S.
- NREM > REM: Dominates at the start of sleep.
- Process S favors NREM sleep: NREM is the priority stage of sleep.
Process C (Circadian Rhythm): Regulates alertness and arousal.
- Melatonin: Hormone associated with Process C.
- NREM < REM: Dominates at the end of sleep.
- REM rebound: Increase in REM sleep after a night of restricted REM.
- Process C is controlled by the SCN: Suprachiasmatic nucleus (SCN) is the brain's master clock.

Summary

The timing and duration of sleep are regulated by both circadian and homeostatic processes.
The two-process model helps explain how sleep pressure builds and declines throughout the day.
Sleep deprivation leads to increased sleep pressure, resulting in daytime sleepiness and an increased need for NREM sleep during the subsequent sleep opportunity.