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Related Concept Videos

Biological Clocks and Seasonal Responses02:45

Biological Clocks and Seasonal Responses

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The circadian—or biological—clock is an intrinsic, timekeeping, molecular mechanism that allows plants to coordinate physiological activities over 24-hour cycles called circadian rhythms. Photoperiodism is a collective term for the biological responses of plants to variations in the relative lengths of dark and light periods. The period of light-exposure is called the photoperiod.
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Disturbances in Heart Rhythm01:29

Disturbances in Heart Rhythm

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Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
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Pulse rhythm01:30

Pulse rhythm

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Pulse rhythm refers to the pattern of pulsations within specific intervals, offering valuable insights into the regularity or irregularity of the heart's beats as observed through the pattern of pulsation within specific intervals. A regular pulse exhibits a consistent heart rate with uniform waveforms and pulsation force, variations of which can be classified as normal, weak, or bounding.
Conversely, an irregular pulse pattern is termed dysrhythmia, stemming from disruptions in cardiac...
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ECG Interpretation of Rhythms01:24

ECG Interpretation of Rhythms

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An electrocardiogram (ECG)graphically represents the heart's electrical activity on ECG paper or a monitor.
Components of the Electrocardiogram
The primary components of a normal ECG waveform in Normal sinus rhythm(NSR) include the P wave, PR interval, QRS complex, ST segment, T wave, and occasionally a U wave.
ECG waveforms are divided by vertical and horizontal lines at standard intervals.
The horizontal axis measures time and rate, and the vertical axis measures amplitude or voltage....
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Electrophysiology of Normal Cardiac Rhythm01:19

Electrophysiology of Normal Cardiac Rhythm

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The normal cardiac rhythm is a synchronized electrical activity that facilitates the regular and coordinated contraction of the heart muscle. This process is essential for efficient blood circulation throughout the body. The fundamental elements involved in establishing and maintaining this rhythm include the unique electrical properties of cardiac muscle cells, the sinoatrial (SA) node's pacemaker function, the specialized conducting system, and the ionic mechanisms underlying each phase...
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Circadian Rhythms and Gene Regulation02:19

Circadian Rhythms and Gene Regulation

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The biological clock is involved in many aspects of regulating complex physiology in all animals. It was in 1935 when German zoologists, Hans Kalmus and Erwin Bünning, discovered the existence of circadian rhythm in Drosophila melanogaster. However, the internal molecular mechanisms behind the circadian clock remained a mystery until 1984, when Jeffrey C. Hall, Michael Rosbash, and Michael W. Young discovered the expression of the Per gene oscillating over a 24-hour cycle. In subsequent...
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Melatonin reduces kainate-induced lipid peroxidation in homogenates of different brain regions.

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Related Experiment Video

Updated: Jan 26, 2026

Design and Analysis of Temperature Preference Behavior and its Circadian Rhythm in Drosophila
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Design and Analysis of Temperature Preference Behavior and its Circadian Rhythm in Drosophila

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The melatonin rhythm: both a clock and a calendar

R J Reiter1

  • 1Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78284-7762.

Experientia
|August 15, 1993
PubMed
Summary

Melatonin production by the pineal gland signals daily and seasonal time to organisms. The duration of elevated melatonin directly correlates with night length, conveying crucial photoperiod information.

Area of Science:

  • Endocrinology
  • Chronobiology
  • Neuroscience

Background:

  • The pineal gland produces melatonin rhythmically.
  • Melatonin secretion follows distinct patterns across species.
  • Melatonin signaling provides daily and seasonal time cues.

Purpose of the Study:

  • Review data on melatonin's role in timekeeping.
  • Summarize nocturnal melatonin production patterns.
  • Identify melatonin receptor functions and locations.

Main Methods:

  • Review of existing scientific literature.
  • Analysis of melatonin production patterns in relation to photoperiod.
  • Discussion of melatonin receptor distribution and function.

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Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents
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Monitoring Cell-autonomous Circadian Clock Rhythms of Gene Expression Using Luciferase Bioluminescence Reporters

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Related Experiment Videos

Last Updated: Jan 26, 2026

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Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents
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Main Results:

  • Nocturnal melatonin duration is proportional to night length.
  • Melatonin rhythms adjust to photoperiod, signaling season.
  • Receptors in the suprachiasmatic nuclei (SCN) may mediate clock signals.
  • Receptors on pars tuberalis cells likely mediate seasonal reproductive changes.
  • Melatonin receptor distribution is species-specific.
  • Some melatonin functions may not require receptors.

Conclusions:

  • Melatonin is a key endocrine signal for both circadian and seasonal timing.
  • Specific melatonin receptors are crucial for conveying time-of-year information.
  • Further research is needed to understand non-receptor-mediated melatonin functions.