The brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. In humans it is usually described as including the medulla oblongata, pons, and midbrain. Less frequently, parts of the diencephalon are included.
The brainstem provides the main motor and sensory innervation to the face and neck via the cranial nerves. Of the twelve pairs of cranial nerves, ten pairs come from the brainstem. Though small, this is an extremely important part of the brain as the nerve connections of the motor and sensory systems from the main part of the brain to the rest of the body pass through the brainstem. This includes the corticospinal tract, the posterior column-medial lemniscus pathway, and the spinothalamic tract.
The brainstem also plays an important role in the regulation of cardiac and respiratory function. It also regulates the central nervous system, and is pivotal in maintaining consciousness and regulating the sleep cycle. The brainstem has many basic functions including heart rate, breathing, sleeping, and eating.