Tegmentum mesencephali

The midbrain is anatomically delineated into the tectum (roof) and the tegmentum (floor).

The midbrain tegmentum extends from the substantia nigra to the cerebral aqueduct in a horizontal section of the midbrain.

It forms the floor of the midbrain that surrounds below the cerebral aqueduct as well as the floor of the fourth ventricle while the midbrain tectum forms the roof of the fourth ventricle.

The tegmentum contains a collection of tracts and nuclei with movement-related, species-specific, and pain-perception functions.

The general structures of midbrain tegmentum include red nucleus and the periaqueductal grey matter.

Nigrostriatal Pathway and Mesolimbic Pathway in the Dopaminergic System

Unlike the midbrain tectum (which is a sensory structure located posteriorly), the midbrain tegmentum, which locates anteriorly, is related to a number of motor functions.

Within the tegmentum, the red nucleus is in charge of motor coordination (specifically for limb movements) and the periaqueductal gray matter (PAG) contains critical circuits for modulating behavioral responses to pains.

The substantia nigra (black substance) serves an important role in rewarding behaviors such as approaching desired objects.

In addition, the substantia nigra forms reciprocal connections with the basal ganglia which are highly correlated with motor functions and learning.

The midbrain tegmentum is also an important part of the dopaminergic system which is essential for feelings of reward and pleasure.

Two regions in the midbrain tegmentum are of particular interest.