The diencephalon is the central part of the forebrain, between the cerebral hemispheres and the midbrain, built around the third ventricle. Its modelled parts, the thalamus, hypothalamus, pineal gland and third ventricle, are lit together. [1][2]
Not lit: the habenula (with the pineal gland it makes up the epithalamus), the subthalamus with its subthalamic nucleus, and the posterior pituitary. The first two are not separate shapes in this 3D model, so no marker is placed at a guessed position; the posterior pituitary grows from the diencephalon, but the model’s pituitary is one shape that includes the front lobe, which does not, so it stays dark. [1][3][4][5][6]
The 3D brain needs JavaScript. The text below still says where the diencephalon is and what it does.
Slice
All 4 are lit together, on both sides where they are paired; tap a name in the list to focus one. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Where it is
It sits between the telencephalon (the cerebral hemispheres) and the midbrain, almost completely covered by the hemispheres. [1][2]
The thalamus forms its upper part and the hypothalamus its lower part; the epithalamus (pineal gland and habenula) sits at the back, and the subthalamus lies below the thalamus. [1][7]
What it does
Almost every sensory signal heading for the cerebral cortex passes through a thalamic relay first; smell is the main exception, reaching the cortex directly. [2][7]
Through the hypothalamus and the pituitary gland, it links the nervous system to the endocrine (hormone) system. [8][2]
Connections
The optic nerves meet at the optic chiasm on its underside; the optic tracts then run to the lateral geniculate nucleus of the thalamus, the relay for vision. [9][10]
Other names
Diencephalon means “between-brain” or “through-brain” (Greek dia, through, and enkephalos, brain); it is also called the interbrain. It is the one region of the adult brain that keeps its name from the embryo, where it grows from the forebrain vesicle (prosencephalon). [1][2]
Size
On this model the diencephalon together fit in a box about 51 mm front to back, 34 mm top to bottom and 48 mm side to side (the box they fit in, not their volume). [6]
Centre of the hypothalamus compared with the centre of the left thalamus: 22 mm further forward, 12 mm lower, 13 mm closer to the midline; 28 mm apart in a straight line. [6]
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. [6]
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.