A person's chronotype refers to the inherent individual differences in their circadian patterns of activity. These variations explain why some people are 'morning people' (morning larks) while others are 'night owls,' and research indicates that these different chronotypes are linked to differences in sleep regulation.

Chronotype

Analyze the following scenario by identifying the key internal biological structure responsible for the described experience. Explain why this structure is temporarily out of sync with the new environment and identify the most critical external signal that will help it realign over time.

Jet Lag and Biological Rhythms

The sleep-wake cycle is a fundamental circadian rhythm that is internally regulated by the body's biological clock. This process governs the daily pattern of sleeping and waking, ensuring it is synchronized with the 24-hour light-dark cycle of the environment.

Google

Columbia University

- Sleep stages
- Sleep patterns over a lifetime
- Sleep onset
- Sleep regularity
- Biological functions of sleep
- Neural systems underlying sleep
- Sleep deprivation
- General anesthetics
- Sleep disorders
- Tracking Information During Sleep
- Sleep-wake cycle

Sleeping and waking

A hormone that is released by the pineal gland and is important in regulating sleep-wake cycles. Melatonin release is stimulated by darkness and inhibited by light.

Melatonin

A pattern centered around behavioral, biochemical, or physiological fluctuation that repeats every 24 hours. Major value of a circadian rhythm is synchronizing behaviors and body states with environmental changes, providing temporal organization. 

Circadian Rhythms

The suprachiasmatic nucleus (SCN), a structure within the hypothalamus, functions as the brain's primary biological clock. It receives direct input about light levels from the retina, which allows it to synchronize the body's internal rhythms with the external day-night cycle. The SCN then orchestrates these rhythms by sending signals to other parts of the brain, including the pineal gland, to regulate physiological and behavioral outputs.

Suprachiasmatic Nucleus (SCN) as the Brain's Biological Clock

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

https://commons.wikimedia.org

This is a repository of free electronic media.

Wikimedia Commons

Throughout sleep, there are different stages characterized by the presence or absence of types of brain waves. Typically, we cycle through these stages 4-5 times a night, sleeping on average 7-8 hours. These stages are broken down into two categories:

- Non-REM
- REM

Sleep Stages

The partial or total prevention of sleep. Side effects could include hallucinations, but most commonly witnessed effects are increases irritability, decreased ability to concentrate, and episodes of disorientation. Cognitive deficits are noticeable. Prolonged sleep deprivation compromises the immune system in mammals and can lead to death.

Sleep deprivation

The exact reasons we sleep are unclear and hotly debated, but there are four main explanations:

- Energy conservation
- Niche adaptation
- Body restoration
- Memory consolidation

Biological functions of sleep

Sleep library

Sleep regularity refers to whether a person sleeps and wakes at a consistent time. 

Sleep Regularity

Sleep onset is when a person transitions from a state of wakefulness and falls asleep.

Sleep Onset

A drug that renders an individual unconscious. Examples include barbiturates and anesthetic gases. They produce slow waves in the EEG that resemble the ones seen in slow wave sleep, suggesting that they tap into existing brain networks that promote sleep. Almost all are non-competitive agonists at GABA(A) receptors, boosting GABA’s inhibitory effect on neurons.

General Anesthetics

This study investigated sleepers' abilities to filter and allocate their attention towards the most relevant source of information when presented with two streams of dialogue. As of the study, there had been no evidence that the sleeping brain could covertly select which piece(s) of information to prioritize when exposed to multiple pieces of information. This study aims to see if the sleeping brain will amplify meaningful speech compared to irregular signals.

"Sleepers Track Informative Speech in a Multi-talker Environment" Legendre et al. (2019)

Sleep Library

Sleep-Wake Disorders are defined using a multidimensional approach due to the expectations for co-existing or comorbid diagnosis in both mental and neurological health. They are largely characterized by individual’s interpretation of having dissatisfying sleep quality, timing, or amount of sleep. These complaints are often expressed alongside issues of distress or impairment during expected daytime activities. 

Sleep-Wake Disorders

Sleep-Wake Cycle

Sleep-wake cycles are regulated by several brain areas working together. The thalamus, hypothalamus, and pons are key regions in this coordination: the hypothalamus includes the SCN, described as the body's biological clock, other hypothalamic nuclei work with the thalamus to regulate slow-wave sleep, and the pons helps regulate rapid eye movement (REM) sleep.

Brain Areas Regulating Sleep

An internal biological clock that allows animals to proceed with their circadian rhythms. Usually, the internal clock is dependent on light. However, animals will still continue their circadian rhythm even in the absence of external cues. For example, even if it is constantly light or dark, animals will proceed with their circadian rhythm. 
- free running

Endogenous clock and circadian rhythm

Irregular sleepers had less exposure to light during the day compared to regular sleepers. Irregular sleepers also had a smaller difference between the amount of light they were exposed to during the day and during the night. This suggests that the circadian rhythms of irregular sleepers is delayed.

Irregular Sleep and Light/Dark Cycle

Circadian Rhythems during the COVID-19 Pandemic

Psychiatry tends to use the circadian cycle to explain illness genesis and illness vulnerability. This is most prominant for mood disorders where a disruption of the 24-hour system occurs before, during and after an episode.

There is also evidence that circadian abnormalities are part of mood disorders functioning as either a cause or a result.

Circadian rhythem involvement in mood disorders

Zeitgebers are environmental cues that help align biological clocks with the external environment. Light is an important cue for setting this clock.

Zeitgebers (time givers)

A collection of symptoms that arises from a mismatch between the body's internal circadian cycles and the external environment. A common cause for this desynchronization is traveling across multiple time zones.

Jet Lag

Based on the following case study, analyze the most likely cause of the nurse's symptoms. Explain how the change in their work schedule leads to these specific physiological and psychological effects, referencing the body's internal 24-hour cycle.

Shift Work and Biological Rhythms

Circadian output rhythms are the daily cycles in physiology and behavior that are controlled by the brain's internal clock, the suprachiasmatic nucleus (SCN). These outputs include rhythms in sleep-wake patterns, hormone release, body temperature, and other bodily functions, ensuring they are synchronized with the 24-hour environment.

Circadian Output Rhythms

The pineal gland is an endocrine structure located within the brain that produces and releases the hormone melatonin. It plays a significant role in regulating various biological rhythms, including sleep-wake cycles, and is also believed to be involved in modulating the immune system during sleep.

Pineal Gland

A research participant is placed in a specially designed room with no windows and is exposed only to constant, dim light for several weeks. Based on the function of the brain's primary biological clock, what is the most likely outcome for their internal daily cycles, such as body temperature and feelings of sleepiness?

A research participant agrees to live in a specially designed laboratory environment for several weeks. The room has no windows, no clocks, and is kept under constant, dim light. Based on the known function of the brain's primary biological clock, what is the most likely outcome for the participant's sleep-wake cycle?

Axons from light-sensitive neurons in the retina carry information about how much light is present to the suprachiasmatic nucleus (SCN), allowing the brain's internal clock to stay synchronized with the outside world.

Retinal Light Input to the SCN

States of consciousness change across the day and across the lifespan, and biological rhythms are important contributors to those changes. Circadian rhythms are a specific biological rhythm involved in these shifts, and they are generated by the suprachiasmatic nucleus (SCN).

Learn Before

Related

Learn After