The diencephalon has four main substructures: thalamus,
hypothalamus, epithalamus, and subthalamus.
We'll focus on the first two.
In Latin, thalamus means little room. In the
brain, the thalamus is located deep inside and between the
two cerebral hemispheres, so it is indeed a little room. The
thalamus is a nuclear mass of great importance in both sensory
and motor systems. No sensory information, with the exception
of olfactory information, reaches the cerebral cortex without first passing through
and being processed by thalamic nuclei.
The thalamus functions as a way station between the brain
and the spinal cord. If you experience sensations such as
pain, pressure, or temperature, you have your thalamus to
thank! Senses such as taste, sight, sound, and touch also
must pass through the thalamus as they make their first stops
in the brain.
The prefix hypo means under, so consider the
hypothalamus as being located under the thalamus. In
medical lingo, the hypothalamus is referred to as inferior
to the thalamus. The lower, or inferior, surface of the hypothalamus
is actually one of the very few parts of the diencephalon
visible on an intact brain. (Remember, the thalamus is the
The hypothalamus is tiny, about the size of a small bean,
and comprises about 1/300th of the brain's total weight. Despite
its unimpressive size, the hypothalamus is the major visceral
control center of the brain. It is your hypothalamus that
regulates your body temperature. And it is your hypothalamus
that sends you a signal to let you know that you're hungry,
thirsty, tired, mad, or sad. The hypothalamus is involved
in limbic system function as well.