The brainstem is continuous with the spinal cord and responsible for vital, unconscious functions such as breathing, regulating the heartbeat, blood pressure, and other important functions. It’s a passageway for ascending and descending tracts. Tracts are bundles of neuron axons in the central nervous system. In the peripheral nervous system, the same structures are called nerves.
The three structures of the brainstem are the medulla oblongata, the pons, and the midbrain. The medulla is the most inferior part and it's continuous with the spinal cord. This part regulates vital functions, for example, heart rate, breathing rate, and swallowing. As this is such a vital area, injuries to the medulla can lead to breathing irregularities, even failure, and loss of sensations.
The pons, or in other words, the bridge, lies in the middle segment of the brainstem. Apart from controlling breathing, it mainly houses nerve tracts that connect various brain parts.
The midbrain, between the pons and diencephalon, is involved in processing visual and auditory information.
Figure 1: Major regions of the brain