The medulla oblongata, or medulla for short, is the part of the brain stem that connects to the spinal cord. Since it is continuous with the spinal cord, there is no clear separation between where the medulla ends and the spinal cord starts. It is arguably the most important part of the brain partly due to its involvement in the heart’s function. The medulla regulates the heart rate and blood pressure. Baroreceptors in the blood vessels detect pressure via the vessels’ expansion and contraction. Using these signals, it sends signals to the heart to pump harder or softer. Chemoreceptors in the blood vessels detect changes in the blood’s oxygen and carbon dioxide levels. Breathing is initiated and regulated due to these responses.
While the medulla is hailed for its involvement in the cardiovascular system, it is responsible for other reflexive actions like coughing, sneezing, swallowing, and vomiting. The part of the medulla that is responsible for vomiting reflexes is not protected by the blood-brain barrier. When potentially toxic substances in the blood are detected, the neurons in that area of the medulla trigger vomiting. Several arteries pass through the medulla, thus allowing it to easily and directly receive signals from blood.
Upon a sudden sight or sound, the medulla will trigger a flight-or-flight response that could include stopping digestion, raising heart rate and blood pressure, and higher alert levels. The medulla also plays a role in sweating and internal body temperature. The startle response would include an increase in sweat production and a raise in body temperature as a result of the increased blood flow. A faster breathing rate would also ensue in order to compensate for the increased oxygen usage.
The medulla contains neurons that activate during rapid eye movement (REM) sleep. Whether or not these neurons play a causal role in REM sleep has yet to be seen. However, it has been shown that a pathway in the medulla of mice promotes REM sleep.