Tegmentum | Brain Parts

Tegmentum

Ashley Davidoff MD

Definition

The tegmentum (latin for covering) is the part of the midbrain that lies anterior to the 4th ventricle. It houses the substantia nigra and he red nuccli. Functionally it is involved with homeostattic mechanisms.

The Tegmentumum (mesencephalon) in Context

Part of the Mesencephalon

The basic and simplest classification of the brain into forebrain midbrain and hindbrain is shown in this diagram and advanced to a more complex tree using the embryological and evolutionary terminologies.

The midbrain or mesencephalon and the Tectum is depicted in a salmon orange.

The forebrain consists of the cerebrum also called the prosencephalon, which contains the more advanced form of the brain and the thalamic structures which contain more basic structures. The cerebrum (telencephalon) itself consists of two cerebral hemispheres and paired basal ganglial structures. Each cerebral hemisphere will have gray and white matter distributed in the frontal parietal temporal and occipital lobe, with the basal ganglia being part of the gray matter deep in the cerebral hemispheres. The most important thalamic structures arising from the diencephalons include the thalamus itself and the hypothalamus. The midbrain (mesencepaholon) consists of the tectum tegmentum and cerebral peduncles. The hindbrain has two major branch points based on the evolutionary development. The pons and cerebellum(part of the metencephalon) are grouped and the medulla (part of the myelencephalon is the second branch.

Midbrain (mb) Tectum (t) and Tegmentum (tg)

Connecting the Forebrain with the Hindbrain

The midsagittal section view of brain reveals the distinctive shape position and character of the midline structures of the brain. The distinction between the character of the cerebral cortex which has a creamy color and the white matter exemplified by the corpus callosum (c) and septum pellucidum (sp) which are white, and the midbrain (mb) with the tegmentum anteriorly (tg) and the tectum (t) posteriorly. The pons (p) and medulla (m) which are off white are part of the hindbrain The cerebellum (c) aso part of the hindbrain is light salmon pink. The relative sizes of the forebrain, midbrain and hindbrain and their components are well appreciated in this section.

Image Courtesy of Thomas W.Smith, MD; Department of Pathology, University of Massachusetts Medical School. 97805b03

Basic Parts of the Midbrain

The midbrain consists of a larger anterior portion called the cerebral peduncles incorporated into the tegmentum or floor of the midbrain (orange ). The posterior portion is called tectum or the roof (yellow/orange) The tegmentum and tectum are separated by the aqueduct of Sylvius (black)

Image provided by Philips Medical Systems Enhanced by Davidoff art Courtesy Ashley Davidoff MD 92141.3kb01bab02.8s

Basic Divisions of the Midbrain

Tegmentum and Tectum

Cerebral Peduncles, Cerebral Crura and Colliculli

The midbrain consists of a larger anterior portion consisting of the cerebral peduncles, (green) the substantia nigra (black) and the tegmentum (light orange) that extends to the aqueduct (thin gray line) The posterior portion called tectum (orange) contains the colliculi (purple) which are the most posterior portions of the midbrain. brain anatomy neuroanatomy midbrain tegmentum colliculi tectum cerebral peduncle aqueduct of Sylvius conceptual diagram MRI principles

Image provided by Philips Medical Systems Enhanced by Davidoff art Courtesy Ashley Davidoff MD 92141.3kb01ba02b02.8s

Tegmentum Substantia Nigra and the Cerebral Peduncles

The anterior border iof the midbrain incorporates the cerbral peduncles(green), and the substantia nigra (black – just posterior to the peduncles. Between the substantia nigra and the aqueduct is an area of the midbrain called the tegmentum (floor of the midbrain) The posterior end of the midbrain, posterior to the aquedct and behind the thin purple line is the tectum (roof) and it houses the colliculi (purple) .

The Cerebral Peduncles Sunstantia Nigra

The Tegmentum and the Tectum

The T2 weighted MRI series focuses on the midbrain with characteristic shape and the small aqueduct of Sylvius posteriorly. The cerebral crura are now shown anteriorly (green) in the cerebral peduncles, and the colliculi are shown posteriorly in the tectum or roof posteriorly