Along the roof of the third ventricle, in the region of the corpora quadrigemina, the meninges which cover the brain also surround the pineal gland. At only about 5 to 8 millimeters long and 9 millimeteres wide, this little cone shaped gland begins to shrink during childhood, right around the age of 7. In an adult human body, its appearance is misleading, as it resembles little more than a mass of fibrous tissue.
Highly specialized parenchymal cells and neuroglial cells make up the pineal gland. Only the autonomic nervous system innervates the pineal gland. Despite its location, the pineal gland is devoid of direct innervation or nervous connection from the brain. The superior cervical ganglion from the autonomic nervous system is responsible for the innervation fo the pineal gland.
The pineal gland is a common gland shared by most mammals, and in some creatures, its function is clearly understood. In humans, however, its function remains somewhat misunderstood. It is known to administer melatonin. It has been proven to adhere to rhythmical patterns of day and night and adapt to seasonal changes. It is unclear what melatonin provides for humans. It has been determined that melatonin directly affects the hypothalamus and encourage the release of some releasing agents. Others have speculated that melatonin directly impacts the sleep cycle. While there is some evidence supporting melatoninís probably role in sexual development, the evidence has not yet been proven beyond theory. Too much melatonin has been proven to delay the initial onset of puberty.