Biological rhythms are defined as a periodic, more or less regular, fluctuation in a biological system that may or may not have psychological implications. Infradian rhythms are a certain type of biological rhythm that is a occurring less frequently than once a day, such as birds migrating, Seasonal Affective Disorder, and the menstrual cycle.

Seasonal Affective Disorder (SAD) is an infradian rhythm that affects many people. It is characterized by certain symptoms, including depression, constant drowsiness, constant hunger, carbohydrate cravings, and a frequent feeling of being lethargic. Though there are numerous sufferers of this disorder, there is no instant cure. One treatment for the disorder is a special kind of light treatment where the person suffering from SAD uses a special light that is more like natural sunlight as opposed to an indoor light.

Another infradian rhythm is the Menstrual Cycle in women. The entire menstrual cycle is a complex cause and effect series. During the first half of the cycle, there is an increase in the woman's estrogen levels, which causes the uterus to thicken. Around mid-cycle, ovulation occurs which in turn causes

A Circadian Rhythm is a cycle that occurs at least once every 24 hours, like sleeping, or change in body temperature. These rhythms are controlled by the body's 'biological clock' located in the hypothalamus, called the SCN (suprachiasmatic nucleus). The SCN regulates our body's melatonin and produces internal synchronization. When certain cycles are thrown out of their usual cycle, the result is internal desynchronization.

Another type of drug is a depressant (like alcohol or tranquilizers). Depressants slow down the activity of the Nervous System. In moderation, depressants can alter the user's perception, slow down their response time, hinder their coordination and balance, and decrease the flow of serotonin, therefore impairing memory. In larger doses, depressants cause insensitivity to pain (emotional and physical), insensitivity to other sensations, convulsions, and can inhibit brain centers that are involved with breathing and heart rate, resulting in death.

The last theory of dreaming is that dreams are intercepted brain activity. In this 'activation-synthesis theory' (first developed by Allan Hobson) dreams are not actually dreams at all, but random firing of neurons during REM sleep. These neurons stimulate the portions of the brain that are responsible for identifying various sensory experiences during waking, and therefore force them to try and make sense of the spontaneous stimulation.

During a single night of sleep, the body goes through the four stages of sleep from one to four, and then goes backwards, from four to one. Following that portion of the cycle, the body slips into REM. This process repeats itself, each time increasing the length of time spent in REM sleep.

PMS (Pre-menstrual Syndrome) is also an infradian rhythm. Some causes of PMS are a progesterone deficiency, levels of progesterone and estrogen are imbalanced, the level of sodium in the bod

Some common words found in the essay are:
Circadian Rhythm, Allan Hobson, Nervous System, Sigmund Freud's, Rosalind Cartwright, Menstrual Cycle, Disorder SAD, Pre-menstrual Syndrome, Biological Rhythms, Affective Disorder, type drug, nervous system, infradian rhythm, rem sleep, menstrual cycle, muscle mass increase, theory dreams, unconscious wishes, central nervous, muscle mass, mass increase, seasonal affective disorder, central nervous system,
Approximate Word count = 1279
Approximate Pages = 5 (250 words per page double spaced)