Part of the epithalamus, the pineal body is a small endocrine gland that produces melatonin, a hormone that affects the modulation of wake/sleep patterns. It is shaped like a pine cone (hence its name) but is only the size of a pea. It is a midline structure located just above the superior colliculi and, and is often seen in X-rays, as it is usually becomes calcified with age. The pineal gland is innervated by peripheral sympathetic and parasympathetic nerve fibers as well as by nerve fibers originating in the central nervous system proper. Descartes regarded it as the principal seat of the soul and the place in which all our thoughts are formed.
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