Circadian Rhythms and SCN Overview

Circadian Rhythms

• Early psychologists believed sleep-wake cycles relied on environmental cues.
• In 1922, a researcher proposed the body generates its own sleep-wake cycles.
• Circannual rhythms are internal mechanisms for annual sleep-wake cycles.
• Circadian rhythms are internal mechanisms regulating 24-hour cycles.
• Sunlight, exercise, meals, and temperature reset circadian rhythms.
• Disruptions to circadian rhythms cause depression, irritability, and poor performance.
• Jet lag disrupts circadian rhythm due to crossing time zones.
• Night shift work disrupts circadian rhythms.

Suprachiasmatic Nucleus (SCN)

• The SCN is a brain region controlling circadian rhythms, sleep, and body temperature.
• SCN damage leads to inconsistent body rhythms and difficulty syncing with light/dark cues.
• SCN single cells regulate tissues responding to circadian rhythms.

Genes and Biochemistry

• Period and timeless genes produce proteins increasing SCN neuron activity.
• The pineal gland, part of the endocrine system, regulates sleepiness by producing melatonin.
• Melatonin secretion typically begins 2-3 hours before bedtime.

Stages of Sleep

• Stage 1 sleep is the initial stage of sleep, with declining brain activity.
• Stage 2 sleep is characterized by sleep spindles and K-complexes.
• Stages 3 and 4 sleep, now combined, feature slow brain waves.
• REM sleep is rapid eye movement sleep, characterized by muscle relaxation and dreaming.

Brain Mechanisms for Arousal

• The reticular formation in the midbrain controls arousal.
• The pontomesencephalon contributes to arousal.
• The locus coeruleus in the pons releases norepinephrine, arousing the cortex. It is inactive during sleep.
• The hypothalamus controls sleepiness, releasing histamine. Antihistamines can induce sleepiness.
• Orexin, a peptide neurotransmitter, promotes wakefulness, released by hypothalamus and basal forebrain.
• GABA and acetylcholine also play roles in wakefulness.

Sleep Disorders

• Sleepwalking occurs when parts of the brain are awake while others sleep.
• Lucid dreaming is awareness of being asleep and dreaming.
• Insomnia is inadequate sleep.
• Sleep apnea is trouble breathing during sleep.
• Narcolepsy involves frequent sleepiness, paralysis, and hallucinations.
• Periodic limb movement disorder involves involuntary leg (and sometimes arm) movements during sleep.
• REM behavior disorder involves movements during REM sleep, potentially due to inadequate inhibitory neurons.
• Night terrors cause intense anxiety and screaming during non-REM sleep.
• Sleepwalking can occur during stages 3 and 4 sleep.
• Sexsomnia involves sexual activity during sleep.

Functions of Sleep

• Sleep provides muscle rest, reduced metabolism, neuronal maintenance, synapse reorganization, memory consolidation, energy conservation, and body temperature regulation.
• Hibernation involves decreased body temperature, offering relative protection against infection and trauma.

Dreaming

• Activation-synthesis hypothesis: Dreaming begins with spontaneous pons activity, activating the cortex.
• Neurocognitive hypothesis: Dreaming is a result of brain activation from multiple areas, including senses, cortex, and internal stimulation.

Explore the fascinating world of circadian rhythms and the role of the suprachiasmatic nucleus (SCN) in regulating sleep-wake cycles. This quiz covers historical perspectives, types of rhythms, and factors that influence these biological clocks. Test your understanding of how disruptions can affect mental and physical health.