The brainstem is made up of all the unpaired structures that connect the cerebrum with the spinal cord. Most rostral (forward) in the brainstem are structures often collectively referred to as the diencephalon. These structures are the epithalamus, the thalamus, the hypothalamus, and the subthalamus.
Directly beneath the diencephalon is the midbrain, or mesencephalon, and beneath the midbrain are the pons and medulla oblongata, often referred to as the hindbrain.
The cerebellum connects the midbrain, the pons, and the medulla. Connections between adjacent structures is completed through paired fiber bundles called peduncles. The cerebellum is capable of providing rapid and decisive responses to stimulus, resulting in almost reflexive type actions.