1.5 Sleep

Sleep is a big deal for how we act and feel. Our sleep/wake cycle follows a circadian rhythm, which is like our body's internal clock, controlled by a part of the brain called the suprachiasmatic nucleus. When this rhythm gets messed up (like with jet lag or working night shifts), it can really throw us off.

Sleep has different stages, including non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. These stages are key for memory, brain restoration, and those wild dreams we have. Knowing about sleep disorders and keeping good sleep habits is crucial for staying on top of our physical and mental health game.

quick cram review

• the sleep/wake cycle controls energy, mood, and thinking.
  • circadian rhythm → 24-hour body clock regulating sleep and alertness.
  • REM sleep → important for memory and dreaming.
  • deep sleep → restores body and brain.
  • lack of sleep → worsens focus, mood, and decision-making.

Sleep/wake cycle effects on behavior

Levels of consciousness

Consciousness = how aware we are of stuff going on inside and outside our bodies.

😳 During wakefulness, we experience:

• High levels of awareness and responsiveness
• Active engagement with our environment
• Clear perception of stimuli

😴 In contrast, sleep is characterized by:

• Reduced awareness of surroundings
• Decreased responsiveness to external stimuli
• Altered states of consciousness

Circadian rhythm and disruptions

Our body's internal clock runs on about a 24-hour cycle, controlled by the suprachiasmatic nucleus (SCN) in the brain. This biological timekeeper responds to environmental cues, especially light and dark.

Common disruptions include:

• Jet lag from crossing time zones
• Shift work schedules, especially if they keep changing
• Irregular sleep schedules
• Exposure to artificial light at night (aka doom scrolling)

These disruptions can lead to:

• Trouble falling asleep, staying asleep, or staying awake
• Feeling foggy-headed
• Changes in appetite (hangry) or mood
• Feel physically off (tired, queasy)

Stages of sleep

Sleep progresses through multiple stages throughout the night, each serving distinct biological purposes.

NREM sleep consists of three stages:

1. Stage 1: Light sleep transition

   • Brief duration
   • Easily awakened
   • Hypnagogic sensations

2. Stage 2: Intermediate sleep with some specific brain wave patterns

   • Sleep spindles appear
   • K-complexes present on EEG
   • Decreased body temperature

3. Stage 3: Deep sleep with slow brain waves

   • Slow-wave activity
   • Difficult to wake
   • Critical for physical restoration

These stages change throughout the night, with the deepest sleep happening earlier on.

REM sleep characteristics

REM sleep is a unique state that combines aspects of both sleep and wakefulness. During this phase, the brain becomes highly active while the body remains largely paralyzed.

Key features include:

• Rapid eye movements (even though they are closed)
• Muscle atonia (so you don't act out your dreams)
• Vivid dreaming
• Increased brain activity

The timing and duration of REM periods follow a predictable pattern:

• First REM period occurs about 90 minutes after falling asleep
• Later REM periods become progressively longer, with longest happening in the morning
• REM rebound occurs after REM deprivation

Theories of dream function

Dreams serve multiple potential functions in cognitive processing and emotional regulation. The two main scientific theories explain dreams through different mechanisms.

Activation-synthesis theory proposes that:

• Dreams result from the brain interpreting random neural firing
• The brain creates narratives to make sense of this activity
• Dream content reflects this synthesis process

Memory consolidation theory suggests that:

• Dreams help process daily experiences
• Emotional memories are integrated during dreaming
• Dream content often incorporates recent events

Sleep's role in memory

Sleep plays a vital role in learning and memory formation. During sleep, the brain processes and stabilizes new information while clearing away unnecessary data. aka you need to sleep before big tests!

Memory consolidation occurs through:

• Neural replay of daytime experiences
• Strengthening of important synaptic connections
• Transfer of information to long-term storage

The restoration process involves:

• Clearing metabolic waste from the brain
• Replenishing neurotransmitters
• Optimizing neural networks for new learning

Sleep disorders and effects

Sleep disorders can significantly impact daily functioning and overall health. Understanding these conditions is crucial for proper diagnosis and treatment.

Common sleep disorders include:

• Insomnia (difficulty falling or staying asleep)
• Narcolepsy (excessive daytime sleepiness or suddenly falling asleep)
• Sleep apnea (interrupted breathing during sleep)
• REM sleep behavior disorder (physically acting out dreams)
• Somnambulism (sleepwalking)

These conditions can lead to various effects:

1. Cognitive impacts:

   • Reduced attention span
   • Impaired decision-making
   • Memory problems

2. Physical effects:

   • Increased accident risk
   • Weakened immune system
   • Weight gain
   • Cardiovascular issues

3. Emotional consequences:

   • Mood swings
   • Irritability
   • Increased anxiety
   • Depression risk