Suprachiasmatic nucleus

Suprachiasmatic Nucleus

The Suprachiasmatic Nucleus (pronounced soo-pra-kai-uh-mat-ik noo-klee-uhs), often abbreviated as SCN, is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle, using around 20,000 neurons.

Etymology

The term "Suprachiasmatic" is derived from Latin roots. "Supra" means above, "chiasmatic" refers to the optic chiasm, the part of the brain where the optic nerves partially cross. "Nucleus" is a Latin term meaning "kernel" or "core", used in anatomy to denote the central part or core of an object or body.

Function

The primary role of the SCN is to control circadian rhythms. These are physical, mental, and behavioral changes that follow a daily cycle. They respond primarily to light and darkness in an organism's environment. The SCN receives information about illumination through the eyes. The retina of the eye contains "classical" photoreceptors ("rods" and "cones"), which are used for conventional vision. But the retina also contains specialized ganglion cells that are directly photosensitive, and project directly to the SCN where they help in the regulation of the circadian rhythms.

Related Terms

• Circadian rhythms
• Hypothalamus
• Optic chiasm
• Retina
• Photoreceptors

See Also

• Biological clock
• Chronobiology
• Melatonin
• Pineal gland

External links

• Medical encyclopedia article on Suprachiasmatic nucleus
• Wikipedia's article - Suprachiasmatic nucleus

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