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Located deep inside the middle of our brain—in the exact center of our brain, actually—is our pineal gland. It's the only endocrine gland that is in contact with the outside world, and it senses when we're exposed to light, much in the way that a security-type light sensor does. The pineal gland has cells that resemble the back of the retina, but it is nestled deep in our brain, far away from any direct access to light.
In some animals—for instance, chameleons—it senses light directly through the skull. In human beings, it likely senses light through special receptors in the backs of our eyes that don't actually provide vision but do dictate our circadian rhythms. Even the blind have this rhythm, indicating that our pineals along with other neurological inputs can substitute for these special cells in our eye.
In some animals—for instance, chameleons—it senses light directly through the skull. In human beings, it likely senses light through special receptors in the backs of our eyes that don't actually provide vision but do dictate our circadian rhythms. Even the blind have this rhythm, indicating that our pineals along with other neurological inputs can substitute for these special cells in our eye.
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