Tectum and tegmentum

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Brainstem and related structures.

The midbrain is the most superior portion of the brainstem, the connection central between the brain and the spinal cord. There are three main parts of the midbrain that include:

• The tectum;
• The tegmentum;
• The cerebral peduncles.

The tectum is the region of the midbrain posterior to the cerebral aqueduct of Sylvius. It contains the nuclei of the superior and inferior colliculi. These colliculi are involved in preliminary processing of the visual (superior colliculi) or auditory stimuli (inferior colliculi) before they reach their corresponding primary processing centers. 

Between the cerebral aqueduct and the pars compacta of the substantia nigra, is the larger portion of the midbrain called the tegmentum (Latin for ‘hood’). The tegmentum in the broader sense extends through the whole brainstem, but its superior portion forms a part of the midbrain. It contains two areas named after specific colours: the red nucleus (involved in the coordination of movements); the periaqueductal grey matter (involved in pain processing). The tegmentum in the midbrain also contains connections within the reticular formation that play a key role in alertness.