The pineal gland is near the centre of the brain on the midline, between the two halves of the thalamus, tucked into a groove where they join, just behind the third ventricle, resting between the superior colliculi of the midbrain. [1]
The 3D brain needs JavaScript. The text below still says where the pineal gland is and what it does.
Slice
Opens cut by a side (sagittal) slice through the pineal gland. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Takes part in: sleep, hormones — see every part of each lit together.
Where it is
It lies in a depression between the two superior colliculi of the midbrain, between the two thalami, and behind the habenular commissure. [1]
It sits in the quadrigeminal cistern behind the third ventricle, enclosing the pineal recess. [1]
Below and somewhat behind the thalamus (the hypothalamus, by contrast, is below and in front of it). [2]
A single (unpaired) midline structure, part of the epithalamus, attached to the rest of the brain by the pineal stalk. [1][3]
What it does
Its pinealocytes make and secrete the hormone melatonin, derived from serotonin. [2]
Light reduces melatonin production and darkness increases it, so blood levels fall in daylight and rise in the evening; melatonin helps set sleep patterns and may influence the other circadian rhythms of appetite and body temperature. [2][1]
When you cross time zones, melatonin production can take several days to adjust to the new light-dark pattern, which is part of jet lag. [2]
Children have higher melatonin levels than adults; this may hold back the release of the pituitary’s reproductive hormones until puberty. [2]
Connections
Light reaches it indirectly: light-sensitive ganglion cells in the retina signal the suprachiasmatic nucleus of the hypothalamus, which relays through the spinal cord and the superior cervical ganglion to the pineal gland. [1][2]
Its stalk is continuous with the posterior commissure below and the habenular commissure above. [1]
It sits outside the blood–brain barrier and has a rich blood supply, second only to the kidney, from branches of the posterior cerebral artery. [1]
Inside it
Mostly pinealocytes arranged in lobules, with four other cell types, surrounded by connective tissue and covered by a capsule of pia mater. [1]
Other names
Also called the pineal body or epiphysis cerebri. “Pineal” is from Latin pinea, “pine cone”, for its shape; Galen called it konarion, “small cone”. [1]
René Descartes called it the “principal seat of the soul”. In some amphibians and reptiles it is linked to a light-sensing parietal or “third” eye. [1]
Size
About the size of a grain of rice: 5 to 8 mm long in humans, reddish-grey. [1]
It grows until about one to two years of age and then stays the same size, though its weight rises gradually from puberty. [1]
On this model the pineal gland measures about 11 mm front to back, 8 mm top to bottom and 6 mm side to side (the box it fits in, not its volume). [4]
Centre of the pineal gland compared with the centre of the left thalamus: 14 mm further back, 9 mm lower, 13 mm closer to the midline; 21 mm apart in a straight line. [4]
Centre of the pineal gland compared with the centre of the pituitary gland: 41 mm further back, 16 mm higher; 44 mm apart in a straight line. [4]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.