Brain Stem: a key structure in the “central nervous system.” A division of the brain attaching the brain to the rest of the body. It includes three main parts – the "midbrain," the "pons," and the "medulla." (Koch, 331) Funnel-shaped structure with a bulbous out-pouching in the middle. (Fisch, 2) Connected to the “diencephalon,”  the “cerebellum,” and the “spinal cord.” (Blumenfeld, 38) The stalk emerges from below the brain and continues as the spinal cord. (SAM Dec08/Jan09, 21)

The major route by which the "cerebral hemispheres” send information to and receive information from the spinal cord and “peripheral nervous system.” (RamachandranTTB, 296) Responsible for the most basic functions of life such as breathing, heart rate, and blood pressure. (Chudler, 31) The most ancient part of the brain -- it evolved more than 500 million years ago and it is rather like the entire brain of present-day reptiles. (Carter, 17) Allows us to attend selectively to specific memories. (Ramachandran, 17)

Medulla Oblongata"caudal" most portion of the brain stem. (Patestas, 81) A major relay station for the crossing of “motor neuron”  “tracts”  between the spinal cord and brain. (Fields, 316) Lower part of the brain that connects to the spinal cord. Contains clusters of cells or "nuclei" that control critical functions like blood pressure, heart rate and breathing. Its upper portion connects to the pons. (Ramachandran, 9) Also referred to as the ‘medulla’ and the ‘myelencephalon.”

Midbrain: see “biological development:nervous system development.”

Tectum: dorsal aspect of the midbrain. (Patestas, 80) Roof of the midbrain. Its functions are "sensory" processing, particularly visual and auditory, and producing 'orienting' movements. (Kolb, 51)

Inferior Colliculus: the posterior pair of the (structures) which contain centers for auditory function. (MeSH) Reflex center for auditory signals. (Patestas, 23) Associated with the ‘medial geniculate (nucleus)’. (Patestas, 80)

Superior Colliculus: the anterior pair of the (structures) which contain the centers for visual function. (MeSH) Reflex center for visual signals. (Patestas, 23) Structure that forms a bump on the roof of the brain stem. The colliculus helps to determine the location of an object. (SAM. Dec08/Jan09, 21) Associated with the “lateral geniculate (nucleus). (Patestas, 80)

Tegmentum: the region of the midbrain below the ("aqueduct of Sylvius"). Floor of the midbrain. A collection of nuclei with movement-related, species-specific, and pain-perception functions. (Kolb, 51)

Pons: part of the central nervous system, located at the base of the brain, between the medulla oblongata and the midbrain. It is part of the brainstem. (NCIt) Region of the brain most closely associated with breathing and with circuits that generate respiratory rhythms. Forms a bridge between the “cerebrum” and cerebellum and is involved in motor control, posture, and balance. It is also involved in sensory analysis and is the site at which auditory information enters the brain. (3D Brain) The medulla is on the floor of the pons. The cerebellum is on the roof of the pons. (Ramachandran, 18)

Pyramidal Decussation: located at the junction between the “medulla” and the “spinal cord.” Area of nerve tracts crossing over to the opposite side of the body. (Blumenfeld, 32)

Reticular Formation: a tangle of neurons in the brain stem that projects widely to vast regions of the brain. Area in which nuclei and fiber “pathways” are mixed, producing a netlike appearance. (Kolb, 51) Various distinct populations of cells embedded in a network of (axons and dendrites) occupying the central core of the brainstem. (In evolutionary terms), an ancient neural complex that is closely associated with two other ancient neural systems, the “olfactory system” and the “limbic system.” (Like these systems), participates in “visceral” functions and “behavioral” responses. (Patestas, 241) Part of the brain stem in charge of general “arousal.” (Goldberg, 22) (Also sometimes used to refer to) any gray matter that is unlabeled in diagrams. (S.Goldberg, 66)