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Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics
in 2 minutes or less.
In this installment I will discuss the suprachiasmatic nucleus.
The suprachiasmatic nuclei, or SCN, are two small, paired nuclei found in the hypothalamus;
they are involved in maintaining circadian rhythms, or biological patterns that follow
a 24-hour cycle.
To accomplish this, the cells of the SCN contain biological clocks.
The following is a simplified description of the molecular mechanism of the biological
clocks in the mammalian SCN.
Cells in the SCN produce two proteins called Clock and BMAL1.
Clock and BMAL1 bind together and promote the expression of genes called period, or
per, and cryptochrome, or cry.
The protein products of these genes, Per and Cry, then bind together and inhibit the actions
of Clock and BMAL1, which in turn suppresses the production of Per and Cry.
Gradually, however, the Per and Cry proteins break down.
When Per and Cry degrade fully, Clock and BMAL1 are free to act again; they go back
to promoting the expression of per and cry, starting the cycle anew.
The process consistently takes around 24 hours to complete before it repeats.
It is thought that this cycle of gene expression is what acts as the molecular clock in SCN
cells, although the process is actually more complex as there are multiple period and cryptochrome
genes as well as other proteins involved in the complete mechanism.
The SCN can use information it receives from the retina about light in the environment
to make adjustments to the circadian clock.
Such information travels from the retina to the SCN along a path called the retinohypothalamic
tract.