The spinal cord is connected to the brain by the brain stem. The medulla oblongata connects the spinal cord to other structures in the brain stem and the brain proper. The brain stem is responsible for some the most basic processes of survival, including the control of hunger, thirst, blood pressure, body temperature and breathing.
In humans, the brain stem consists of three structures: the medulla oblongata, the pons and the midbrain. The medulla oblongata is responsible for the cardiac, respiratory and vasomotor centers that control blood pressure, heart rate and breathing. This structure also controls the reflex centers responsible for vomiting, sneezing, coughing and swallowing. The medulla oblongata is estimated to have evolved in vertebrate organisms approximately 505 million years ago in early fish, as it is present in primitive fish species such as hagfish and lampreys.
The pons structure lies between the midbrain and the medulla oblongata. It is responsible for carrying neural signals from the cerebellum to the medulla oblongata and for carrying sensory signals to the thalamus. This signal relay function makes the pons significant in sensory functions such as equilibrium, taste, touch and hearing. The midbrain is responsible for carrying signals to other areas of the brain significant to hearing, vision and motor control. It is also responsible for sleep/wake arousal and body temperature regulation. The pons and midbrain are very primordial nervous system structures, being present in vertebrate organisms from common insects to humans.