Topic 9: Sleep I: Circadian Rhythms

Circadian Rhythm

A biological cycle that repeats approximately every 24 hours.

Biological Clock

An internal timing system that regulates daily physiological and behavioural rhythms.

Circadian Timing System

The network of structures that generates and regulates circadian rhythms.

Sleep-Wake Rhythm

The daily cycle of sleeping and waking controlled by circadian processes.

Suprachiasmatic Nucleus (SCN)

A group of neurons in the hypothalamus that acts as the body's master clock.

Hypothalamus

A brain structure involved in regulating homeostasis hormones and circadian rhythms.

Master Clock

The primary biological clock that coordinates rhythms throughout the body.

Zeitgeber

An external cue that synchronizes circadian rhythms.

Light

The most important environmental cue regulating circadian rhythms.

Retina

A light-sensitive structure in the eye that detects environmental light levels.

Retinohypothalamic Pathway

A neural pathway that carries light information from the retina to the SCN.

Entrainment

The process by which circadian rhythms synchronize with environmental cues.

Melatonin

A hormone that helps regulate sleep and circadian rhythms.

Pineal Gland

An endocrine gland that releases melatonin.

Melatonin Release

The secretion of melatonin that typically increases in darkness.

Darkness

A cue that promotes melatonin production and sleepiness.

Alertness

A state of wakefulness influenced by circadian rhythms.

Body Temperature Rhythm

A daily fluctuation in body temperature regulated by the circadian clock.

Hormonal Rhythm

Daily patterns of hormone release controlled by circadian processes.

Cortisol

A hormone that typically peaks in the morning to promote alertness.

Sleep Pressure

The increasing drive to sleep that builds during wakefulness.

Homeostatic Sleep Drive

The process that increases the need for sleep the longer a person remains awake.

Circadian Phase

A specific point within the circadian cycle.

Phase Shift

A change in the timing of circadian rhythms.

Advanced Phase Shift

A shift causing sleep and wake times to occur earlier.

Delayed Phase Shift

A shift causing sleep and wake times to occur later.

Jet Lag

A temporary disruption of circadian rhythms caused by rapid travel across time zones.

Shift Work

A work schedule that often disrupts normal circadian rhythms.

Circadian Misalignment

A mismatch between internal biological rhythms and the external environment.

Chronotype

An individual's natural preference for sleeping and waking at particular times.

Morning Type

A person who naturally prefers earlier sleep and wake times.

Evening Type

A person who naturally prefers later sleep and wake times.

Sleep Hygiene

Behaviours that promote healthy sleep patterns.

Artificial Light

Human-made light that can disrupt circadian rhythms especially at night.

Blue Light

A wavelength of light that strongly influences circadian timing and melatonin suppression.

Circadian Regulation

The control of physiological and behavioural processes according to a 24-hour cycle.

Biological Rhythm

A recurring cycle in biological processes.

Homeostasis and Circadian Rhythms

Circadian rhythms work with homeostatic processes to regulate sleep and body function.

Circadian Disruption

A disturbance of normal biological rhythms that can affect health and sleep quality.

Daily Rhythms

Predictable physiological and behavioural changes occurring across the day.

Internal Timekeeping

The biological process that allows the body to track time independently of external cues.