The pineal gland is located where the meninges of the corpora quadrigemina surround the brain. This cone-shaped gland measures 9 millimeters wide and 5 to 8 millimeters long. It starts to shrink when a person is 7 years old and continues to adulthood where it looks like a little fibrous tissue.
The pineal gland is composed of specialized parenchymal cells and neuroglial cells. It gets innervated by the autonomic nervous system, and only that. Even if the pineal gland is located in the brain, it does not receive innervation from the brain. The superior cervical ganglion of the autonomic nervous system is specifically in charge of this innervation.
The pineal gland exists in most mammals, and its function is explicitly recognized in some organisms. But, that does not include human beings. The reason for existence of the pineal gland isn’t exactly known. What’s known about it is the following: it produces melatonin, it helps the person adapt to seasonal changes and time differences. It stops there, though. Melatonin, for one, is not clearly understood. Science knows that it affects the hypothalamus and triggers the production of some agents. Others think that it has an effect on a person’s sleep cycle. Then there are some who believe that it may play a role in sexual development, but that is still a theory. It has been found out, too, that an abnormally high level of melatonin in the body can delay puberty.