Ask JaniceLiving organisms developed an internal biological clock, called the Circadian rhythm, to help their bodies adapt to the daily cycle of day and night- light and dark as the Earth rotates every 24 hours. Our body works differently from hour to hour, day to day and year to year. These patterns of change occur in all living organisms. Chronobiology studies the biological rhythms; ultradian rhythms are shorter than a day with a length, from thousandths of a second (like the pulses in neurons) or seconds (like the heartbeat) to the rhythm of about 90 minutes in our sleeping cycle from sleep to deep sleep, circadian rhythms, which last about 24 hours and infradian rhythms, longer than a day. The most well know is the female cycle, another cycle is the week, it has a biological basis – the immune system has a weekly rhythm. The biological clock (a term used long before the clock was created), is a piece of brain made up of two tiny clusters of several thousand nerve cells that “tell time” based on external cues, such as light and darkness. This region of the brain is referred to as the suprachiasmatic nucleus (SCN), located very close to the optic nerve where it can get information directly from the eyes. Circadian rhythms are controlled by "clock genes" that carry the genetic instructions to produce 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. Daylight resets the internal biological clock every day so it is synchronized with a 24-hour day Air travel to a distant time zone can also disrupt normal cycles. Jet lag is a disconnect between local time and your body's time. Once you arrive at your destination, the change in daylight hours will reset your internal clock, but it will take a few days to get rid of the jet lag. The human circadian rhythm is not exactly 24 hours - it's actually 10 to 20 minutes longer. Other species have circadian rhythms ranging from 22 to 28 hours. The biological clock in living organisms keeps working even when the organism is removed from natural light. Without daylight, the biological clock will eventually start running on its own natural cycle. If you lived in an underground bunker under constant artificial light, you would continue to follow an approximately 24-hour sleep-wake pattern, but your cycles would slowly get out of phase with actual daytime and nighttime. But as soon as morning light hits the eyes, the clock will reset to match the earth's 24-hour day. Why aren't organisms' internal clocks exactly 24 hours long? A theory is the competition for food and other resources is most intense among species with 24-hour cycles. If you eat at the same time as everyone else, you're less likely to get your share. Our slightly out of sync internal clock may have evolved to help us survive the competition. Biological clocks also play a role in longer cycles such as hibernation, bird migrations and even annual changes in the color of a hamster's coat. When the animal brain records longer days in the spring and shorter days in the fall, it triggers hormone secretion that influences these events. Light is the main signaling influencing circadian rhythms: The hormone melatonin is most important in the control of the rhythms. Production of melatonin is in the pineal gland also referred to as the “third eye” and is directly influenced by light. In mammals it is influenced through the eyes. When it gets dark the gland starts the production of melatonin, when it gets light again it stops. During longer nights more melatonin n is produced. Irregularities in melatonin production can cause sleep problems, lethargy and mood disorders. The neurotransmitter serotonin is believed to influence mood and brain activity. Many antidepressants on the market today are used to help in production of serotonin. Interestingly melatonin and serotonin cannot be produced at the same time. Serotonin and melatonin work in conjunction with each other. When serotonin levels are high melatonin levels are held in check – and visa versa. After the lights are out at night your melatonin levels rise and your serotonin levels fall. The morning light immediately starts suppressing melatonin levels and allowing the rise in serotonin. Getting outside in the natural light helps this process and allows a full release of serotonin for the day’s use. Many believe that seasonal affective disorder (SAD) is partly caused by high melatonin levels due to the lack of exposure to light which act to suppress serotonin release. The message here is: get out in the light in the morning and turn down the lights at night. Janice Gaines Jan 2012