The diencephalon is a part of the brain that is located between the cerebral cortex and brain stem. It contains a number of components, including the thalamus, hypothalamus, and epithalamus. Each of these components plays an important role in regulating our behavior and emotions.

The thalamus is the largest of the diencephalon components. It functions as a relay center for sensory information to and from the cortex. It also plays a role in some types of learning and memory.

The hypothalamus is responsible for regulating hormones and controlling the autonomic nervous system. It is also involved in the control of body temperature, hunger, and thirst.

The epithalamus is composed of the habenular nucleus and the pineal gland. The habenular nucleus is involved in the regulation of sleep, while the pineal gland produces melatonin, a hormone that helps regulate sleep and wakefulness.

Out of the three diencephalon components, the one that is not a part of it is the cerebellum. The cerebellum is located at the back of the brain and plays an important role in motor control and coordination.

In conclusion, the cerebellum is not a diencephalon component. The diencephalon consists of the thalamus, hypothalamus, and epithalamus. Each of these components plays a crucial role in regulating our behavior and emotions.