<p>Suprachiasmatic nucleus: accumulation of a few thousand nerve cells, located above (supra) the intersection of the optic nerve (chiasm). It is now considered as the main regulator of the circadian clock. Each of the nerve cells in the SCN has its own internal clock. Normally, the internal clocks of these cells are synchronized and thus enhance the timing signal to a strong common control signal for the circadian clock<img class="buttons square13 zippy-plus" src="http://www.google.com/images/cleardot.gif" border="0" /></p>