Gland
Pineal gland
Also called Epiphysis, Pineal body
A tiny pine cone deep in the brain that releases melatonin when darkness falls.
The pineal gland is a tiny gland shaped like a pine cone, tucked at the back of the diencephalon. When it gets dark, it releases melatonin, a hormone that tells your body it is night and helps time sleep. Light hitting your eyes, especially bright bluish light, shuts melatonin down through signals from the brain's master clock. The philosopher René Descartes famously called it the "seat of the soul".
Where it is
Deep in the center of the brain, at the back of the third ventricle, just above the top of the brainstem and between the two halves of the thalamus.
What it does
Night signal
It releases melatonin into the blood mostly at night, telling your body it is time to wind down.
Follows the master clock
It takes its orders from the suprachiasmatic nucleus in the hypothalamus, which tracks light and dark.
Marking the seasons
Longer winter nights mean longer melatonin release. Many animals use this to time breeding.
Think of it as the brain's night-light in reverse: it switches on only when the lights go out.
Works with
- HypothalamusIts master clock tells the pineal gland when it is day or night.
- Spinal cordThe clock's message takes a detour down into the spinal cord and back up before reaching the gland.
- HabenulaIts close neighbor, attached near its base.
- Third ventricleThe fluid-filled space it sits at the back of.
- Optic nerve (II)Where the light information that controls it first enters the brain.
When it goes wrong
Calcification
Calcium deposits commonly build up in the pineal gland with age and show up on X-rays and CT scans. This is usually harmless.
Pineal tumors
Rare growths here can press on the top of the brainstem, causing trouble looking upward and a buildup of brain fluid.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- Descartes picked it as the "seat of the soul" partly because he believed it was the only part of the brain not doubled into left and right copies.
- The "it is dark" message takes a strange detour: from the brain's clock down into the spinal cord, out to a nerve cluster in the neck, and back up into the skull.
By the numbers
Where the name comes from
From Latin "pinea", meaning "pine cone", because of its shape.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the pineal gland?
Show the answer
Night signal. It releases melatonin into the blood mostly at night, telling your body it is time to wind down.
Night signal. It releases melatonin into the blood mostly at night, telling your body it is time to wind down.
The pineal gland is part of which larger structure?
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Diencephalon. It belongs to the diencephalon.
Diencephalon. It belongs to the diencephalon.
Which part fits this description? "Like the brain's night-light in reverse: it switches on only when the lights go out."
Show the answer
Pineal gland. It is the pineal gland. A tiny pine cone deep in the brain that releases melatonin when darkness falls.
Pineal gland. It is the pineal gland. A tiny pine cone deep in the brain that releases melatonin when darkness falls.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Physiology, Pineal Gland, StatPearls, NCBI Bookshelf
- 15.2 Where Are Rhythms in the Brain?, OpenStax, Introduction to Behavioral Neuroscience
- Descartes and the Pineal Gland, Stanford Encyclopedia of Philosophy
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