Sleep and Wakefulness Lecture Review

Chapter 44

Sleep

A condition of body and mind recurring after a period of several hours, characterized by closed eyes, relaxed muscles, altered brain activity, and usually a state of suspended consciousness.

N1 Sleep

The first stage of the sleep cycle, characterized by drowsiness, slowing eye movement, decreasing brain activity, and some spontaneous muscle activity.

N2 Sleep

The 'lighter' or intermediate stage of sleep, representing about 50% of total sleep time, characterized by decreased muscle movement, fluctuating brain activity, and the appearance of sleep spindles.

Sleep Spindles (N2)

Random bursts of electrical activity in the brain during N2 sleep, caused by communication between the thalamus and cortex due to leaky calcium channels and brief sodium spikes.

N3 Sleep

The deepest stage of sleep, characterized by the lowest brain activity, eye movement, and muscle activity, and the appearance of slow wave sleep spindles (large, wide peaks on EEG) due to random cortical neuron activation.

REM Sleep (Rapid Eye Movement)

A stage of sleep characterized by rapid eye movement, brain activity similar to wakefulness (body asleep, brain awake), vivid dreams, and importance for memory consolidation, emotion processing, and learning.

Non-REM Sleep

Stages N1, N2, and N3 of sleep, where the body and brain are at rest; crucial for tissue repair, muscle growth, regulation of metabolism, blood pressure, and the immune system (homeostasis), and essential for survival.

Arousal System

Brain circuitry and neuronal communication (primarily glutaminergic, dopaminergic, and some acetylcholine) responsible for keeping an individual awake; lesions in key areas can lead to a coma.

Sleep System

Brain circuitry primarily involving GABAergic neurons that inhibits the arousal system, helping to turn off cortical activity and induce sleep.

Modulatory System

A system involving biogenic amines (serotonin, norepinephrine, histamine) that contributes to both arousal and sleep, produced mainly by neurons in the brainstem.

Coma

A permanent unconscious state of the brain characterized by significantly diminished cortical activation, though brainstem activation may maintain vital functions.

Locked-in Syndrome

A condition where an individual maintains consciousness and brain function but is completely paralyzed and unable to move or speak.

Serotonin (Sleep Role)

A neurotransmitter that generally promotes non-REM sleep and suppresses the ability to transition into the REM cycle.

Histamine (Sleep Role)

A neurotransmitter that promotes wakefulness; its levels typically drop during non-REM sleep.

Norepinephrine (Sleep Role)

A neurotransmitter that promotes arousal and wakefulness while simultaneously turning off sleep circuitry.

Acetylcholine and Dopamine (Sleep Role)

Neurotransmitters that promote REM sleep, specifically enhancing this phase of the sleep cycle.

Glutamate (Sleep Role)

The main excitatory neurotransmitter that functions as the primary driver of the arousal system, promoting wakefulness.

GABA (Sleep Role)

An inhibitory neurotransmitter whose role in sleep and wakefulness is complex, inhibiting either arousal or sleep circuitry depending on the specific neurons it targets.

Circadian Rhythm

A biological process that operates under a roughly 24-hour cycle, synchronizing an individual's sleep-wake cycle with environmental light-dark cues and internal biological clock genes.

Sleep Pressure

A homeostatic drive to sleep that accumulates throughout the day due to metabolic activity (e.g., ATP usage creating adenine) and decreases during sleep.

Suprachiasmatic Nucleus (SCN)

A region of the hypothalamus containing neurons with biological clock genes, serving as the body's master clock to regulate various biological processes and melatonin release, activated by retinal light input.

BMAL1 and CLOCK Genes

Key clock genes that undergo a 24-hour transcription-translation cycle, dimerize, and activate the transcription of CRY and PER genes within the SCN.

CRY (Cryptochrome) and PER (Period) Genes

Genes transcribed and translated in response to BMAL1 and CLOCK; their protein products accumulate, dimerize, and then inhibit BMAL1 and CLOCK, creating a negative feedback loop essential for the 24-hour circadian cycle.

Insomnia

A sleep disorder characterized by difficulty falling asleep, difficulty staying asleep, or both, often linked to unusual activation of the arousal system and treated with GABA-promoting drugs or antihistamines.

Sleep Apnea

A sleep disorder where an individual temporarily stops breathing during sleep due to collapsed airways, leading to oxygen deprivation; regulated by the brainstem and often treated with a CPAP device.

Narcolepsy

A sleep disorder characterized by an irresistible urge to fall asleep at inappropriate times, non-restful sleep, and sometimes symptoms like hallucinations or sleep paralysis (pieces of REM sleep occurring during wakefulness).