Brain Stem

Portion of the brain comprising the medulla oblongata, pons and midbrain. The name pons is derived from the Latin word "pons" meaning "bridge". It is the crossover point for ascending sensory and descending motor tracts linking higher and lower centers, and for transverse fiber pathways entering and leaving the cerebellum on each side. Its significance lies in the fact three cranial nerves arise from it and along with the medulla oblongata it regulates the rate and depth of breathing. The three nerves are the sixth cranial (abducens), seventh cranial (facial) and the eighth cranial (vestibuloocular). The medulla oblongata or, as it is more often called, the medulla is a bulbous structure that resembles the spinal cord that is continuous with the pons above and the spinal cord below. The medulla comprises vital nuclei and white matter that form the descending and ascending communication tracts between the spinal cord and the brain. Various cranial nerves arise from the medulla, including the glossopharyngeal, accessory, hypoglossal and vagus. Other nuclei within the medulla function as autonomic centers for controlling vital visceral functions including heartbeat, arterial blood pressure and rate and depth of breathing