Chapter 1. The Suprachiasmatic Nucleus

Infographics Activity
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The suprachiasmatic nucleus (SCN) of the hypothalamus is the body’s internal master clock, playing a role in regulating our circadian rhythms. These rhythms roughly follow the 24-hour cycle of daylight and darkness. But one doesn’t have to consciously perceive light for the SCN to function properly: there is a dedicated, nonvisual pathway that carries light information from the eyes to the SCN.

The figure shows human brain. Reticular formation regulates alertness and sleepiness. Pineal gland produces melatonin. Hypothalamus regulates patterns of hunger and temperature. The Suprachiasmatic nucleus (SCN) is actually two tiny bundles of neurons within the hypothalamus. The SCN sends messages about light to the rest of the hypothalamus and the reticular formation, and regulates the pineal gland’s production of melatonin, a sleep-inducing hormone. The SCN is located deep in the brain, far away from visual processing areas. So how does it get information about light. Our eyes contain a separate nonvisual pathway made of retinal ganglion cells. This pathway goes directly to the SCN. For the 20 percent of the U.S. workforce doing shift work, normal sleep schedules are disrupted. This leads to health problems and increased accidents (Harrington, 2001). Using what we know about how the SCN works, researches are helping industries ease these effects. Bright light, such as those installed in this power station control room, contain a high proportion of the light found in morning sun, fooling the SCN into thinking it is daytime. That makes it easier for workers to synchronize sleep patterns with work activities.

QUESTION: Before he goes to sleep one night, Liam sets the alarm clock on his cell phone for 7:30 the next morning. He makes a mistake, though, and chooses 7:30 pm instead of 7:30 am. At around 7:20 the next morning, he wakes up all by himself, even though the cell phone never rang. Thankfully, the part of his brain called the __________ acted as his own internal alarm clock and he did not miss his important meeting at work.
Correct.
Incorrect.

QUESTION: Which of the following structures does not seem to be specifically involved in the regulation of the sleep-wake cycle?
Correct.
Incorrect.

QUESTION: After she got home from work, Louise decided to spend the whole evening working on the project she needed to complete for work. She sat at her desk, typing on her computer for several hours before she took a break. When she stood up she was surprised to find how much time had passed, and noticed that it was already dark outside. Very soon after she started feeling very sleepy and yawning. Which hormone has probably been released in higher amounts in Louise’s bloodstream in the last several minutes?
Correct.
Incorrect.

QUESTION: Julian was born blind, and has never had a “visual” experience. He sees nothing, not even shades of light or black and white. Given what Infographic 4.1 says about light and the sleep-wake cycle, do you think that Julian will be more likely to feel tired when it is dark outside than when it is light outside?
Correct.
Incorrect.

QUESTION: Which part of the endocrine system is responsible for increased secretion of melatonin when it is time for a person to get sleepy?
Correct.
Incorrect.

QUESTION: If you were the manager of a security company whose job it was to provide overnight monitoring of computerized security systems, which of the following would you be advised to do to help your nighttime workers synchronize their sleep patterns with their work demands?
Correct.
Incorrect.

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