Sleep

Sleep – A state of relative unresponsiveness to the environment, regulated by biological clocks (circadian rhythm).

Circadian Rhythm – 24-hour internal clock influencing sleep timing.

Electroencephalogram (EEG) – Non-invasive measurement of neural activity.

N1 (Stage 1) – Transitional stage of sleep; alpha waves → theta waves.

N2 (Stage 2) – Deeper relaxation; dominated by theta waves, sleep spindles, and K-complexes.

N3 (Stage 3) – Deep slow-wave sleep; delta waves (<3 Hz).

REM (Rapid Eye Movement) Sleep – Sleep stage with darting eye movements; brain waves resemble wakefulness; vivid dreaming occurs.

Sleep Spindles – Bursts of neural activity in N2; important for learning and memory.

K-Complexes – Large waves in N2; responses to external stimuli.

Suprachiasmatic Nucleus (SCN) – Hypothalamic nucleus generating circadian rhythms; receives light input.

Pineal Gland – Releases melatonin, promoting sleep onset.

Preservation & Protection Theory – Sleep conserves energy and protects vulnerable animals.

Body Restoration Theory – Sleep repairs tissues, releases growth hormone, lowers metabolism.

Brain Maintenance Theory (REM) – REM sleep provides neuronal exercise; critical for sensory-motor development.

Suprachiasmatic Nucleus (SCN) – Hypothalamic nucleus; master circadian clock.

Pineal Gland – Releases melatonin to promote sleep.

Hypothalamus – Regulates sleep and circadian rhythms.

Thalamus – Relay station; involved in sensory input during sleep.

Pons & Reticular Formation – Involved in sleep regulation, especially REM.