The brain stem connects the brain with the spinal cord, with which it is continuous. In the brain stem are regulating areas for all kinds of functions of which we are not aware. For example regulation ofpressure and heart rate, muscle tension of vessel walls, control of breathing and of body temperature. In this it is closely related to the hypothalamus. The degree of consciousness is controlled by the reticular formation, which has an important role in sleep. The brain stem also contains scattered islands of grey matter, groups of nerve that give rise to the majority of the cranial nerves. These cranial nerves control many functions of the head and neck. An exception is the vagus nerve (the tenth cranial nerve), which extends from the medulla oblongata of the brain stem through the chest and into the abdomen. It is part of the parasympathetic nervous system, serving the vocal cords, lungs, heart and stomach. It has both sensory and motor functions.
By this we can see that the brain stem is indispensable for the maintainance of life. Therefore brain stem death has come to be synonymous with death. The recognition of brain stem death is of great importance in patients whose vital functions, such as breathing, have been taken over by life support machines.