How does the biological clock tick

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How does biological clock tick?

What is Biological Clock:

A clock that runs in our body is often overlooked but is found in all major groups of organisms. It tells us to maintain the rhythmicity in our daily life and has certain characteristics like period, free-running rhythm, entertainment, Zietgebers, masking etc.

How does biological clock tick

Patterns of Biological Clock:

Based on the period of the rhythm, we come across three major types of rhythm: circadian (20-80 hours), ultradian (20 hours) and infradian rhythm (28 hours).

Influence of Biological Clock:

It has also been observed that if the biological clock is disturbed it leads to depression, seasonal effective disorder and many more. Shift workers and jet lag are some of the common examples of altered biological clock and we can keep this biological clock in time by maintaining a good routine life with a sound sleep.

One of the most common phenomenons that we are living with is the biological clock rhythms. These are found in all major groups of organisms, but very few of us are concerned about it. One of the major characteristics of biological clock is period which in simple words is length of time required to repeat a rhythmic cycle called the period and it has been used to categorize rhythms into three major groups: circadian (20-80 hours), ultradian (20 hours), and infradian (28 hours). 

In nature, there occurs synchronization between circadian rhythms and cycle changes in light dark cycle or temperature. 

When these environmental cues are not present, the rhythm continues but in the form of free running rhythm and it has a period slightly longer or shorter than just 24 hours. 

Biological Clock Variables:

Some typical examples of biological variables for rhythms include (a) change in body temperature in humans and leaf movements of lants show circadian rhythmicity (b) brain waves of humans and twining of movements of bean shoots have ultradian rhythmicity and (c) the menstrual cycle of human females and the annual germination of certain seeds are common examples of infradian rhythms. 

The term ‘circadian’ comes from the Latin word circa, meaning “around” and ‘Diem’ or dies meaning “day”. Collectively, the proper study of different biological temporal rhythms is called as chronobiology or in other words the science that describes timing in biological clocks and their associated rhythms is called chronobiology.

By nature circadian rhythms are endogenous or self-sustaining but they are adjusted to the native environment by external cues or signals called Zietgebers the most important of them is daylight. Light is known to influence the circadian rhythms very strongly as it turn on and turn off certain genes that control the body’s internal clock.

Circadian rhythms can influence some of the significant body functions which include sleep-wake cycle, hormone release, body temperature and son on. Irregular circadian rhythms generally end with obesity, diabetes, depression, bipolar disorder and seasonal effective disorder. 

Properties of Biological Clock:

Time keeping is important at two levels: to time changes in physiology and behavior within each day and within each year. For the former, birds have a system of at least three independent circadian clocks present in the retina of the eyes, the pineal gland, and the hypothalamus. This differs from the situation in mammals in which the input, pacemaker, and output are localized in different structures. When it comes to the biological clock, it is necessary to mention about the master clock that is present in brain and coordinates all the body clocks so that they are in sync. 

Now the question arises what is there in the master clock that regulates the different body clocks in a coordinated manner? This master clock controls circadian rhythms with the help of a group of nerve cells in the brain called the suprachiasmatic nucleus, or SCN. The SCN which is located in the hypothalamus, an area of the brain just above where the optic nerves from the eyes cross contains about 20,000 nerve cells. 

How does biological clock tick

Biological clock have certain properties that describe them, regardless of where they are found:

  • They continue to run under constant conditions: Biological clock produce rhythmic patterns even if the environment cues called Zietgebers are removed. This phenomenn is called free running in terms of chronobiology.
  • They are temperature compensated: Biological clocks are one of the few biological systems that are not subtle to temperature changes. Normally, the activity of many systems alters according to temperature e.g. enzymes catalyse reactions at a faster rate at a warm temperature than cold one. an important property of the clock is temperature compensation, and it is maintained by the clock irrespective of environmental temperature changes or there will be disruptions in clock when there will be temperature variations.
  • They are altered by light: Biological clocks are altered or entrained by light levels and changing lengths of photoperiod. This anticipation of changing day length helps different organisms to adjust accordingly.
  • They are under Genetic Control: It has been observed that the period length of the clock runs shorter or longer than 24 hours if there is alteration in the clock gene expression.
  • They are adjustable: The external environmental cues called Zietgebers which mainly include photoperiod, temperature and social cues allows the clock to run with a rhythm most appropriate for the organisms surroundings.

Physiology of the biological clock:

To study the physiological location of biological clocks a number of animal systems, including humans were studied and it was observed that in most vertebrates other than mammal for example sparrows, biological clock was found to be located in the pineal gland. This gland is located at the base of the brain and is responsible for the production of melatonin, a hormone produced in high levels at night and low levels during the day.

In mammals, additional cells responsible for biological clock functions were located in the hypothalamus, in two clusters of nerve cells called the suprachiasmatic nuclei (SCN). Light receptors in the retina are connected by nerves to the SCN. The SCN and the mammalian pineal gland are linked by both nervous connections and by the presence of melatonin receptors on SCN cells. A cascade is observed in the flow of light transmission from eyes to SCN, which in turn passes the information on to the pineal gland, controlling melatonin production.

The circadian rhythms of humans can be entrained to slightly shorter and longer periods than the Earth’s 24 hours. Recent studies by researchers at the Harvard have reported that human subjects can at least be entrained to a 23.5 hour cycle and a 24.65 hour cycle (the latter being the natural solar day-night cycle on the planet Mars). The action of light on the body rhythms and on the biological clocks is of prime importance as many of the the fundamental processes of the body are controlled by these rhythms. These internal rhythms are usually (via the retinal perception and the clock system) showing up as daily rhythms with a 24 hour period.

What if the biological clock is disturbed:

Systems, like hunger, mental alertness, mood, stress, heart function, and immunity also operate on a daily rhythm. The existence of the biological clock can be clearly understood when it is out of harmony or imbalanced as in the case of jet lag and shift workers. These phenomenons disturb our normal biological clock and affect our physical and mental health badly. Even shifting the clock an hour forward or backward when daylight saving time begins or ends can disrupt our biological clocks.

Many studies have shown that when we work late in night and lose 1- 2 hours sleep, we observe more frequent accidents and workplace injuries due to sleep disturbance.

The best example of biological clock is disturbed in the case of jet lag and shift workers. In the case of jet lag we move abroad to a place with a huge time lag from our own country. When jet lag sets occurs, we feel disoriented, foggy and sleepy at the wrong times of the day because after changing time zones, our body’s biological clock tells us it’s one time and the outside environment tells us it’s another. 

Shift work is another is another example of how we can get ourselves off-cycle, and it also leads into a circadian rhythm disorder over the long term. People who work in night shift not only have a hard time with their sleep patterns, but other systems in their bodies can also feel the effects and they can be chronic. In many cases, weight gain and metabolic disturbances are observed but no connection has still been found.

Biological Clock Controlling Moods: 

The emotional up and downs are also regulated by our internal biological clock. The altered circadian rhythms are generally observed in people with mood disorders like depression, bipolar disorder and seasonal affective disorder.

The relationship between the body rhythms and moods is a complex one, and likely has to do with how the brain chemical serotonin which fluctuates in relation to the light-dark cycle and the throughout the year as the days become longer and shorter. The circadian rhythm is also known to have a connection with the mental health which in turn leads to disease states like Alzheimer’s, Parkinson’s and Huntingtin’s and even autism spectrum disorder.

Studies have shown that normally functioning biological clock is sensitive to light input, so light treatment can be used as a therapy to restore the proper timing of the body rhythms and in terms of biological clock we call it as chronotherapy. This special form of light therapy is sometimes used as an approach for treating depressive disorders.

Keeping the Biological Clock in Time:

In today’s time, paying attention to our body’s natural rhythms is undoubtedly more important to our health than we realize. Most of the times we feel that it is only the sleep deprivation that affects our body, but it is also the variation in our biological rhythms that affect so many body functions, making us more prone to health problems like infection, mood problems and even heart disease.

Why Biological Clock Disorder Happens:

Why biological clock becomes disordered in certain people, or naturally with age, is not completely clear, but some have recently suggested that it could in part have to do with the aging of the eyes as from the studies it has already been known that light is also perceived by the retina and is connected to the nerves with SCN or the suprachiasmatic nucleus which plays an important role in maintaining our biological clock stable.

Therefore, the natural changes in the lens and even the development of cataract reduce the light perceived into the eye and, therefore, the brain; and this can affect biological cock. 

There are many other reasons which lead our bodies’ biological clock to go out of sync, which possibly involve a combination of genetic susceptibility and life style choices. 


Waking up a little earlier, reducing the intake of caffeine late in the day and finishing the last piece of work late night rather than getting up earlier in the morning makes a huge difference in the biological clock functioning and the way of our living. 

Therefore, we conclude that keeping our schedule on track as much as possible is probably the best advice. Wes should have a pretty good sense of our body’s natural rhythms intuitively. Avoid disruptions to our eat-sleep cycles. Practice good sleep hygiene, and stick to a sleep schedule that works well for your body to keep the system in its natural rhythm.

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