A gland named for the cone of a conifer, in the midline of the brain behind the third ventricle
Pineal gland — from Latin pinea, a pine cone.
Anatomy · Glands & the immune system
Pineal gland
A pine-cone-shaped gland deep in the brain
Endocrine system · epithalamus, roof of the third ventricle
A tiny, pine-cone-shaped gland in the midline of the brain, attached by a short stalk to the back of the roof of the third ventricle, between the two cerebral hemispheres and just above the midbrain's superior colliculi. It is only about 5–8 mm long. Its cells, the pinealocytes, make the hormone melatonin, released mainly in darkness, which tells the body the time of day and helps set the sleep–wake cycle.
How to spot them
- ▸A small pine-cone-shaped structure in the midline, at the back of the third ventricle
- ▸Sits above the superior colliculi of the midbrain, tucked beneath the back end of the corpus callosum
- ▸Part of the epithalamus, next to the habenula
- ▸Often calcifies with age, forming 'brain sand' visible on skull X-rays
- ▸Unlike most of the brain it lies outside the blood–brain barrier
What to know
The hormone of darkness, made from serotonin, which peaks at night and is suppressed by light
Pineal gland — melatonin.
The French philosopher who called it 'the principal seat of the soul' (1649)
Pineal gland — René Descartes, in The Passions of the Soul, because it is single and midline while most brain structures come in pairs.
Gritty calcium deposits called 'brain sand' collect in it, and a shift of its calcified shadow on an X-ray can signal a mass elsewhere
Pineal gland — corpora arenacea.
In lizards and the tuatara a related structure forms a light-sensing 'third eye' on top of the head
Pineal gland — the parietal eye belongs to the same pineal complex.
Signals from the eyes reach it via the suprachiasmatic nucleus and a sympathetic relay in the neck
Pineal gland — the route runs through the superior cervical ganglion.
A tumour here can compress the midbrain and blind upward gaze, as in Parinaud's syndrome
Pineal gland — pineal tumours press on the tectum.
Key ideas
- Light on the retina signals the suprachiasmatic nucleus of the hypothalamus, which in the dark drives sympathetic nerves via the superior cervical ganglion to trigger melatonin release in the pineal.
- Melatonin does not switch sleep on by force; it acts as a chemical signal of night, and lag from long-haul travel is sometimes treated with it.
Quick-fire facts
- •About 5–8 mm long and weighing roughly 100–150 mg in adults
- •Its other name is the epiphysis cerebri; it is part of the epithalamus
- •It has no blood–brain barrier; its capillaries are fenestrated so hormone can pass to blood
- •Descartes named it the seat of the soul in the 17th century (1649, The Passions of the Soul)
- •Pinealocytes make melatonin from tryptophan via serotonin
- •Calcified deposits, the corpora arenacea ('brain sand'), accumulate through adult life
- •A calcified pineal in the midline is a classic landmark on skull X-ray and CT
- •In many non-mammalian vertebrates the pineal complex responds directly to light, and in some reptiles forms a 'third eye'
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