Exogenous and Endogenous Factors Affecting Bodily Rhythms

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The Role of Endogenous and Exogenous Factors in Bodily Rhythms: Biological rhythms are cyclical changes in the way biological systems behave, one such rhythm is the sleep-wake cycle in humans and animal. Other rhythms are seasonal such as animals hibernating in the winter or migrating to a new region. But what controls these rhythms?, there are internal biological clocks also called endogenous pacemakers. One such internal “biological clock” is the suprachiasmatic nucleus. In mammals, the main endogenous pacemaker is a tiny cluster of nerve cells called the suprachiasmatic nucleus (SCN), which lies in the hypothalamus. It is located just above the place where the optic nerves from each eye cross-over. The SCN obtains information about light from the eye via the optic nerve. If our endogenous clock is running slow, morning light automatically shifts the clock ahead, putting the rhythm in tune with the world. The SCN sends signals to the pineal gland, located next to the optic nerve, directing the gland to increase production of the hormone melatonin at night. Melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness. In birds and reptiles the pineal gland lies beneath the bone of the skull and is regulated by light; light inhibits the production of melatonin. In fact many lizards have a “third eye” near the pineal gland which actually protrudes through a small opening in the skull and receives information about light. External cues from the environment, called Exogenous Zeitgebers, also control our bodily rhythms; these include sunlight, food, noise and social interaction. Another cue is light, light is the dominant Zeitgeber in humans. As mentioned light can reset the bodies’ main pacemaker, the SCN. However, it can also reset the other oscillators located throughout the body because one of the proteins in the biological clock is CRY,

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