Biological Clock PDF

# Biological Rhythms Biological Rhythms are the natural cycle of change in our body's chemicals or functions. It's like an internal master "clock" that coordinates the other clocks in your body. The "clock" is located in the brain, right above the nerves where the eyes cross. It's made up of thousan...

# Biological Rhythms Biological Rhythms are the natural cycle of change in our body's chemicals or functions. It's like an internal master "clock" that coordinates the other clocks in your body. The "clock" is located in the brain, right above the nerves where the eyes cross. It's made up of thousands of nerve cells that help sync your body's functions and activities. Biological rhythms are an integral part of everyday life for most organisms on earth. They regulate most important functions in each organism. In plant circadian clocks control flowering, response to seasons and photosynthesis. In mammals, circadian clocks manage sleeping, waking, feeding and controlling whether an animal is nocturnal or diurnal. ## Chronobiology Chronobiology is a field of biology that examines periodic phenomena in the biological processes of living organisms. “chrono” means related with time; opbiology means science of life. Thus chronobiology is the study of science of life in relation with time, “biological rhythmicity is an integral part of the organization of living matter. ### Location of Body's Master Clock The master circadian clock that regulates 24-hour cycles throughout our bodies is found in a region called the suprachiasmatic nuclei (SCN) in the hypothalamus of the brain. The SCN is made up of two tiny clusters of several thousand nerve cells that "tell time" based on external cues, such as light and darkness. The SCN regulates sleep, metabolism, and hormone production. ### Circadian Rhythms Circadian rhythms are controlled by "clock genes" that code for clock proteins. The levels of these proteins rise and fall in rhythmic patterns. These oscillating biochemical signals control various functions, including when we sleep and rest, and when we are awake and active. Circadian rhythms also control body temperature, heart activity, hormone secretion, blood pressure, oxygen consumption, metabolism, and many other functions. ### The Tッキング of the Biological Clock The basis of circadian rhythm lies in interactions between certain proteins creating the 'tick' of the biological clock. It is an ingenious negative feedback loop. Darlington et al (1998) first discovered it in fruit flies but actual proteins vary from species to speciesThe protein mechanism is present in SCN (central oscillator) and other cells throughout the body (peripheral oscillators)This explains why different functions have different rhythms. ### The Suprachiasmatic Nucleus (SCN) Tiny cluster of cells, in thehypothalamus, just above optic chiasmObtains info about light via optic nerveIf the sun rises earlier than day before, light resets the clock There is one in each hemisphere, divided into two parts, dorsal and ventral. Ventral is reset much more quickly, dorsal more resistant to being reset as it is less affected by light (Albus et al, 2005). ### Pineal Gland and Melatonin SCN sends signals to pineal gland telling it to increase melatonin at night. Melatonin induces sleep by inhibiting brain mechanisms responsible for alertness. In birds and reptiles this is just below the thin skull bone and so directly affected by light – light inhibits melatonin production. Some lizards have a third 'eye' which sticks out of a small opening in the skull and receives info about light. ### Endogenous Pacemakers and Exogenous Zeitgebers | Endogenous Pacemakers | SCN evidence-'mutant' hamsters | Evolutionary approach | | ------------------------ | -------------------------------- | ----------------------- | | SCN-main EP | Desynchronisation leads to symptoms similar to jet lag | SCN lesions in chipmunks - (de Coursey et al) | | SCN contains protein mechanism | | Non-human animal studies evaluated in terms of ethics and relavance. | | Pineal gland controls melatonin secretion | | | | Exogenous Zeitgebers | | | | Light is dominant zeitgeber | Artifical lighting may also reset biological clock | You could also use studies from rhythms topics to add to your AO2; | | Social cues also important | Failure of biological clock leads to sleep-phase disorders | You just need to make sure you say why they are relavant | | Biological rhythms can be entrained by temperature | Biological clock is really a blend of endogenous and exogenous factors. | | ## Figure 3: Human Biological Clock | Time | Event | Time | Event | | -------- | --------------- | -------- | ------------------------------------------------ | | 02:00 | Deepest Sleep | 12:00 | Noon | | 04:30 | Lowest temperature | 14:30 | Best coordination | | 06:00 | | 15:30 | Fastest reaction time | | 06:45 | Sharpest rise in blood pressure | 17:00 | Greatest cardiovascular efficiency and muscle strength | | 07:30 | Melatonin secretion stops | 18:00 | | | 08:30 | Bowel movement likely | 18:30 | Highest blood pressure | | 09:00 | Highest testosterone secretion | 19:00 | Highest body temperature | | 10:00 | High alertness | 21:00 | Melatonin secretion starts | | | | 22:30 | | | | | 00:00 | Midnight | | | | | Bowel movement suppressed | ## Properties of Circadian Rhythms They are genetic in origin. They are controlled by biological clocks. The biological clocks are reset and calibrated by periodic environmental signals (called synchronizers or Zeitgebers or entraining agents). There are often cycles within cycles, their intensity and frequency varying in different parts of the activity period. ### Circatidal –Tidal Activity Period (Approx 12hrs 25min) Cycle of high and low tides, roughly twice per day. Because the tides aren't exactly 12 hours apart, high and low tide are approximately 50mins later each day. ### Circalunar –Monthly Activity Period (Approx 29days) Some cycles are approximately monthly, resulting from the movement of the moon around the earth. More commonly, these cycles are circasemilunar = twice a month. These are usually the result of spring tides and neap tides'. Spring tides are particularly high tides that occur twice each month when the moon and sun are in alignment (and the gravitational field of the sun contribute to the tides aldar tides are weaker tides where there is much less difference between high and low tide. They occur when the sun and moon are perpendicular to each-other and their gravitational fields have an opposing influence on the tides. ### Circannual -Yearly Activity Period (Approx 365 Days) The earth axis is on a slight tilt, causing a yearly cycle of seasonal changes. Countries experience summer when their hemisphere is tilted towards the sun. It's not warmer because they are any closer to the sun, but because the days are longer. In winter the days are shorter and the sun doesn't rise as high, staying closer to the horizon. The lower angle of Sun during the winter months means that incoming rays of solar radiation is spread over a larger area of the Earth's surface, so the light received is more indirect and of lower intensity. Lower intensity light is less able to heat the ground. Circannual rhythms are often associated with migratory behaviours, hibernation, dormancy, etc. ## Figure 8: Life History Stages of the Annual Cycle of a Seasonal Migrant Peripheral arrow's indicate the clockwise direction of the cycle. Central arrows illustrate annual change in photoperiod with increasing light coloration representing lengthening photoperiods of spring and summer and the darkening portions signifying short day lengths of autumn and winter. Points of contact of medial arrows represent winter and summer solstices. ## Biological Rhythms in Animals If the biological rhythm is controlled by a biological clock it will continue even in the absence of the exogenous (external) stimulus. The behaviour is not a direct response to an environmental factor, but is controlled endogenously -by an internal timing mechanism that is ultimately genetic in origin. It allows the organism to anticipate the environmental change and respond before hand. However, some responses are controlled purely by exogenous (external) factors. In this case the response always follows the environmental change. ### Figure 8: Process of SCN Sending Signals to Body This clock helps regulate functions that include: - sleep schedule - appetite - body temperature - hormone levels - alertness - daily performance - blood pressure - reaction times External factors can influence your biological rhythms. For instance, exposure to sunlight, drugs, and caffeine can affect sleep schedules. ## Types of Biological Rhythm Disorders Disorders may develop when natural biological rhythms are disturbed. These disorders include: ### Sleep Disorders The body is "wired" to sleep at night. Disruptions in the body’s natural rhythms can lead to affected sleep, including insomnia. ### Jet Lag A disruption in circadian rhythms when traveling across time zones or overnight. ### Mood Disorders Lack of exposure to sunlight can lead to conditions like depression, bipolar disorder, and seasonal affective disorder (SAD). ### Shift Work Disorders When a person works outside the typical work day it causes changes in typical circadian rhythms. ## The Effects of Biological Rhythm Disorders Biological rhythm disorders can affect a person’s health and feelings of wellbeing. Some of the effects include: - anxiety - daytime sleepiness - depression - lower performance at work - being more accident-prone - lack of mental alertness - increased risk for diabetes and obesity ## Why Do You Need Seven to Eight Hours of sleep? Some of the world’s most significant human errors have happened during night shift work. These include the Chernobyl disaster and the Three Mile Island accident. Also, most single-driver accidents occur in the time before dawn, according to Cornell University. From a brain and body perspective, our bodies are made to sleep at night. This is why we don't have adaptations like night vision and an enhanced sense of smell and hearing like nocturnal animals do. ## Risk for Biological Rhythm Disorders An estimated 15 percent of full-time workers in the United States work shifts. Shift workers are usually in service-related jobs that are vital to the health and movement of society. They're also more likely to sleep fewer than six hours a night. Those who do shift work, or work outside the typical 9 a.m. to 5 p.m. workday schedule, are especially at risk for biological rhythm disorders. Examples of professions that involve shift work include: - healthcare workers - drivers, pilots, and others who provide transportation - food preparers and servers - police officers - firefighters An NSF survey found that 63 percent of works felt that their work allowed them to get enough sleep. The same survey also found 25 to 30 percent of shift workers have episodes of excessive sleepiness or insomnia. Other groups of people who are at risk for a biological rhythm disorder include people who travel across time zones often or live in places that do not have as many hours of daylight, like Alaska. ## Diagnose Biological Rhythm Disorders? Diagnosing biological rhythm disorders is usually a matter of a careful health history review. A doctor will ask you questions that may include: - When did you first notice your symptoms? - Are there activities that make your symptoms worse? Better? - How do your symptoms affect you? - What medications are you taking? A doctor may also wish to rule out other conditions, like blood sugar disorders, that can cause similar mood disorder symptoms. ## Biological Rhythm Disorders Treatment Treatments for biological rhythm disorders vary and depend on the underlying cause. For example, jet lag symptoms are usually temporary and don't need medical treatment. In cases of shift work disorder or mood disorders, lifestyle changes may help. ## Important Questions ### Short Answer Questions 1. Define biological rhythms. 2. Define circadian rhythms. 3. What are parameters of circadian rhythms. 4. What are names of brain areas responsible for biological rhythm. ### Long Answer Questions 1. What are Endogenous Pacemakers and Exogenous Zeitgebers. 2. Parameters of biological rhythms. 3. Write short notes on: - Zeitgebers - Tidal rhythms - Circalunar rhythms - Circadian rhythms