| Have you ever noticed that when it starts to get | | | | influences commonly include jet lag and working |
| dark you start to yawn, and when the sun is | | | | night shifts. |
| shining on you in the morning it is difficult to stay | | | | Intrinsic circadian rhythm disorders occur when a |
| asleep? This isn't coincidence; it is your body's | | | | person's SCN isn't working correctly. In delayed |
| circadian clock functioning correctly. This is the | | | | sleep phase syndrome, for example, a person will |
| biological clock that every mammal has that tells | | | | become tired much later than normal and want to |
| you to be active during daylight and rest when it | | | | sleep half the day away. These people experience |
| is dark. | | | | peak alertness late at night. Advanced sleep phase |
| The technical term for this clock is the | | | | syndrome is just the opposite. Sufferers will find it |
| suprachiasmatic nucleus, or the SCN. The SCN | | | | difficult to stay awake in the evening, and always |
| consists of two very small brain structures that | | | | wake up very early in the morning. |
| contain about twenty thousand neurons combined. | | | | Perhaps the most interesting of these disorders is |
| Light that hits the photoreceptors in the retina | | | | the twenty five hour sleep phase disorder. |
| creates a signal that is sent along the optic nerve | | | | Although this is considered a disorder, these |
| to the SCN, according to Health Link. | | | | people are actually on the natural human biological |
| One of the major functions of the SCN is that it | | | | clock. Studies have found that when people are |
| controls the production of melatonin. When a light | | | | removed from light and given no time cues, their |
| signal reaches the SCN, it automatically turns off | | | | bodies naturally slip back into a twenty five hour |
| melatonin production. At night, the SCN will | | | | time clock rather than our twenty four hour one. |
| increase the level of melatonin in the body, which | | | | People who have this natural clock normally |
| makes the person drowsy. Other bodily functions | | | | experience peak alertness one hour later each |
| the SCN regulates are body temperature, | | | | day, until it gets back to the beginning and starts |
| hormone secretion, urine production and blood | | | | all over again. |
| pressure. | | | | While none of these disorders are too serious, |
| While most people's circadian rhythm is on time | | | | they can cause insomnia during normal sleeping |
| with normal daily life, some have circadian rhythm | | | | hours. This can be easily fixed by an adjustment |
| disorders that throw them off. Most commonly, | | | | to the person's schedule so that they can sleep |
| these disorders are extrinsic, meaning they are | | | | when their body wants to. |
| developed because of outside influences. Such | | | | |