Intro | Forebrain | Midbrain | Hindbrain
Part 1: Image-Mapped Tutorial
Part 2: Matching Self-Test
Part 3: Multiple-Choice Self-Test
The Midbrain is found at the upper part of the brain stem, between the hindbrain and the forebrain. The midbrain structures control our ability to orient our ears and eyes to important events in our environment.
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The midbrain is also referred to by the Greek name, mesencephalon; which means literally, middle-brain. The roof of the midbrain is called the tectum; it is composed of two visible swellings called the superior colliculus and inferior colliculus (meaning little hill). The collicului of the tectum are involved in the control of movements that orient our sensory receptors to external events of interest. The superior colliculus controls this function for the visual system, whereas the inferior colliculus controls this function for the auditory system. Below the tectum lies the tegmentum (or rug of the midbrain). The tegmentum contains the nuclei for cranial nerves III and IV, portions of the reticular formation, pathways conveying information to and from higher and lower centers of the nervous system, and the substantia nigra. The substantia nigra is a dopamine-containing nucleus with diffuse projections to motor centers of the brain. A depletion of dopamine in the substantia nigra is associated with the movement disorder called Parkinson's Disease. The reduction of dopamine causes a reduction in and slowing of voluntary movement, peculiar posture, muscular tremor at rest, and expression-less face.