The brain stem is the lowest part of the brain. It connects the midbrain to the spinal cord. The brain stem is comprised of the pons located in the upper portion of the brain stem and the medulla oblongata located in the lower portion of the brain stem. The pons is a bundle of nerve fibers linking the left and right sides of the cerebellum. The medulla oblongata’s main function is to relay nerve signals between the brain and the spinal cord. The medulla oblongata also functions to help control autonomic functions including breathing and heart contractions, as well as reflex activities such as swallowing and coughing.