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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 pineal gland.
The pineal gland was given its name because it has a pine-cone like shape.
Unliked most brain structures, the pineal gland is unpaired, meaning there is only one.
It sits directly on the midline of the brain.
The function most linked to the pineal gland is the secretion of a hormone called melatonin,
which is best known for its role in regulating circadian rhythms.
The pineal gland is made up of secretory cells called pinealocytes, which secrete melatonin
throughout the 24-hour cycle.
Secretion is highest in the middle of the night.
It begins to decrease as it gets closer to dawn and is lowest during daylight hours.
This schedule of melatonin secretion is regulated by signals from the retina about light in
the environment, which travel to a nucleus in the hypothalamus called the suprachiasmatic
nucleus and then via an indirect route to the pineal gland.
The main function of the suprachiasmatic nucleus is to control circadian rhythms, and in addition
to sending information about ambient lighting to the pineal gland, the suprachiasmatic nucleus
also uses levels of melatonin as a signal to provide information about the time of day.
Because melatonin levels are highest during the hours of darkness, melatonin activity
can be used as a signal that circadian rhythms should be in their nocturnal stage.
If melatonin levels are high and someone is still wide awake, it is an indication circadian
rhythms are not in sync.
This might happen, for example, after flying across several time zones.
In this case, melatonin is used by the suprachiasmatic nucleus as a signal to get circadian rhythms
back on track.
Due to its close association with nighttime and circadian rhythms, melatonin has also
been investigated as playing a role in promoting sleep, but the true relationship between melatonin
and sleep is still unclear.