Chinese (Mandarin)

Spanish

English

Hindi

Arabic

Portuguese

Bengali

Russian

Japanese

Punjabi

German

Javanese

Malay

Telugu

Vietnamese

Korean

French

Marathi

Tamil

Urdu

Turkish

Italian

Chinese, Yue / Cantonese

Thai

Gujarati

Chinese, Jin

Chinese, Min Nan

Persian, Dari

Persian, Western

Polish

Pashto

Kannada

Chinese, Xiang

Malayalam

Sundanese

Hausa

Odia

Burmese

Chinese, Hakka

Ukrainian

Bihari, Bhojpuri

Tagalog

Yoruba

Bihari, Maithili

Uzbek

Sindhi

Amharic

Fula

Romanian

Oromo

Igbo

Azerbaijani

Chinese, Gan

Dutch

Kurdish, Central

Kurdish, Northern

Kurdish, Southern

Malagasy

Lahnda, Saraiki

Nepali

Sinhalese

Chittagonian

Zhuang

Khmer

Turkmen

Assamese

Madurese

Somali

Marwari

Bihari, Magahi

Haryanvi

Hungarian

Chhattisgarhi

Greek

Chewa

Dakhini

Akan, Twi

Akan, Fante

Kazakh

Chinese, Min Bei

Sylheti

Zulu

Czech

Kinyarwanda

Marwari, Dhundhari

Haitian Creole

Chinese, Min Dong

Ilocano

Quechua

Kirundi

Swedish

Hmong

Shona

Uyghur

Hiligaynon

Mossi

Xhosa

Belarusian

Balochi

Psychology

<OpenstaxParagraph>
	<OpenstaxTerm>Biological rhythms</OpenstaxTerm> are internal rhythms of biological activity. A woman’s menstrual cycle is an example of a biological rhythm—a recurring, cyclical pattern of bodily changes. One complete menstrual cycle takes about 28 days—a lunar month—but many biological cycles are much shorter. For example, body temperature fluctuates cyclically over a 24-hour period (<a href="#Figure_04_01_Rhythms">Figure 4.2</a>). Alertness is associated with higher body temperatures, and sleepiness with lower body temperatures.
</OpenstaxParagraph>
<OpenstaxFigure id="Figure_04_01_Rhythms" src="https://openstax.org/apps/archive/20240226.174525/resources/d2da772dbc0592c5fa2e39d56b50ba466a82bf60" alt="A line graph is titled “Circadian Change in Body Temperature (Source: Waterhouse et al., 2012).” The y-axis, is labeled “temperature (degrees Fahrenheit),” ranges from 97.2 to 99.3. The x-axis, which is labeled “time,” begins at 12:00 A.M. and ends at 4:00 A.M. the following day. The subjects slept from 12:00 A.M. until 8:00 A.M. during which time their average body temperatures dropped from around 98.8 degrees at midnight to 97.6 degrees at 4:00 A.M. and then gradually rose back to nearly the same starting temperature by 8:00 A.M. The average body temperature fluctuated slightly throughout the day with an upward tilt, until the next sleep cycle where the temperature again dropped. " mediaType="image/jpg" width="731" height="449" />
<OpenstaxFigureText width="731">
	<strong>Figure 4.2</strong> This chart illustrates the circadian change in body temperature over 28 hours in a group of eight young men. Body temperature rises throughout the waking day, peaking in the afternoon, and falls during sleep with the lowest point occurring during the very early morning hours.
</OpenstaxFigureText>
<OpenstaxParagraph>
	This pattern of temperature fluctuation, which repeats every day, is one example of a circadian rhythm. A <OpenstaxTerm>circadian rhythm</OpenstaxTerm> is a biological rhythm that takes place over a period of about 24 hours. Our sleep-wake cycle, which is linked to our environment’s natural light-dark cycle, is perhaps the most obvious example of a circadian rhythm, but we also have daily fluctuations in heart rate, blood pressure, blood sugar, and body temperature. Some circadian rhythms play a role in changes in our state of consciousness.
</OpenstaxParagraph>
<OpenstaxParagraph>
	If we have biological rhythms, then is there some sort of <OpenstaxTerm>biological clock</OpenstaxTerm>? In the brain, the hypothalamus, which lies above the pituitary gland, is a main center of homeostasis. <OpenstaxTerm>Homeostasis</OpenstaxTerm> is the tendency to maintain a balance, or optimal level, within a biological system.
</OpenstaxParagraph>
<OpenstaxParagraph>
	The brain’s clock mechanism is located in an area of the hypothalamus known as the <OpenstaxTerm>suprachiasmatic nucleus (SCN)</OpenstaxTerm>. The axons of light-sensitive neurons in the retina provide information to the SCN based on the amount of light present, allowing this internal clock to be synchronized with the outside world (Klein, Moore, &amp; Reppert, 1991; Welsh, Takahashi, &amp; Kay, 2010) (<a href="#Figure_04_01_SCN">Figure 4.3</a>).
</OpenstaxParagraph>
<OpenstaxFigure id="Figure_04_01_SCN" src="https://openstax.org/apps/archive/20240226.174525/resources/a851b18bae062f1b52f4731e93a853e816aa45c5" alt="In this graphic, the outline of a person’s head facing left is situated to the right of a picture of the sun, which is labeled ”light” with an arrow pointing to a location in the brain where light input is processed. Inside the head is an illustration of a brain with the following parts’ locations identified: Suprachiasmatic nucleus (SCN), Hypothalamus, Pituitary gland, Pineal gland, and Output rhythms: Physiology and Behavior. " mediaType="image/jpg" width="649" height="427" />
<OpenstaxFigureText width="649">
	<strong>Figure 4.3</strong> The suprachiasmatic nucleus (SCN) serves as the brain’s clock mechanism. The clock sets itself with light information received through projections from the retina.
</OpenstaxFigureText>

4.1.1 Biological Rhythms

1 Introduction to Psychology

1.1 What Is Psychology?

1.1.1 Why Study Psychology?

1.2 History of Psychology

1.2.1 Wundt and Structuralism

1.2.2 Functionalism

1.2.3 Freud and Psychoanalytic Theory

1.2.4 Wertheimer, Koffka, Köhler, and Gestalt Psychology

1.2.5 Pavlov, Watson, Skinner, and Behaviorism

1.2.6 Maslow, Rogers, and Humanism

1.2.7 The Cognitive Revolution

1.2.8 Multicultural And Cross-Cultural Psychology

1.2.9 Women in Psychology

1.3 Contemporary Psychology

1.3.1 Biopsychology and Evolutionary Psychology

1.3.2 Sensation and Perception

1.3.3 Cognitive Psychology

1.3.4 Developmental Psychology

1.3.5 Personality Psychology

1.3.6 Social Psychology

1.3.7 Industrial-Organizational Psychology

1.3.8 Health Psychology

1.3.9 Sport and Exercise Psychology

1.3.10 Clinical Psychology

1.3.11 Forensic Psychology

1.4 Careers in Psychology

1.4.1 Other Careers in Academic Settings

1.4.2 Career Options Outside of Academic Settings

2 Psychological Research

2.1 Why Is Research Important?

2.1.1 Use of Research Information

2.1.2 NOTABLE RESEARCHERS

2.1.3 The Process of Scientific Research

2.2 Approaches to Research

2.2.1 Clinical or Case Studies

2.2.2 Naturalistic Observation

2.2.3 Surveys

2.2.4 Archival Research

2.2.5 Longitudinal and Cross-Sectional Research

2.3 Analyzing Findings

2.3.1 Correlational Research

2.3.2 Causality: Conducting Experiments and Using the Data

2.3.3 Reliability and Validity

2.4 Ethics

2.4.1 Research Involving Human Participants

2.4.2 Research Involving Animal Subjects

3 Biopsychology

3.1 Human Genetics

3.1.1 Genetic Variation

3.1.2 Gene-Environment Interactions

3.2 Cells of the Nervous System

3.2.1 Neuron Structure

3.2.2 Neuronal Communication

3.2.3 Neurotransmitters and Drugs

3.3 Parts of the Nervous System

3.3.1 Peripheral Nervous System

3.4 The Brain and Spinal Cord

3.4.1 The Spinal Cord

3.4.2 The Two Hemispheres

3.4.3 Forebrain Structures

3.4.4 Midbrain and Hindbrain Structures

3.4.5 Brain Imaging

3.5 The Endocrine System

3.5.1 Major Glands

4 States of Consciousness

4.1 What Is Consciousness?

4.1.2 Problems With Circadian Rhythms

4.2 Sleep and Why We Sleep

4.2.1 What is Sleep?

4.2.2 Why Do We Sleep?

4.3 Stages of Sleep

4.3.1 NREM Stages of Sleep

4.3.2 REM Sleep

4.4 Sleep Problems and Disorders

4.4.1 Insomnia

4.4.2 Parasomnias

4.4.3 Sleep Apnea

4.4.4 Narcolepsy

4.5 Substance Use and Abuse

4.5.1 Substance Use Disorders

4.5.2 Drug Categories

4.6 Other States of Consciousness

4.6.1 Hypnosis

4.6.2 Meditation

5 Sensation and Perception

5.1 Sensation versus Perception

5.1.1 Sensation

5.1.2 Perception

5.2 Waves and Wavelengths

5.2.1 Amplitude and Wavelength

5.2.2 Light Waves

5.2.3 Sound Waves

5.3 Vision

5.3.1 Anatomy of the Visual System

5.3.2 Color and Depth Perception

5.4 Hearing

5.4.1 Anatomy of the Auditory System

5.4.2 Pitch Perception

5.4.3 Sound Localization

Question	Answer
biological rhythm that occurs over approximately 24 hours	circadian rhythm
tendency to maintain a balance, or optimal level, within a biological system	homeostasis
area of the hypothalamus in which the body’s biological clock is located	suprachiasmatic nucleus (SCN)