Welcome to 2 minute neuroscience, where I explain neuroscience topics in 2 minutes or
In this installment I will discuss the midbrain.
The midbrain is one of the three divisions of the brainstem.
At the level of the midbrain, the fourth ventricle has narrowed to form the cerebral aqueduct,
which connects the third and fourth ventricles.
The region of midbrain behind the cerebral aqueduct is called the tectum.
The area in front of the cerebral aqueduct is called the tegmentum.
The anterolateral portion is made up of two structures called the basis pedunculi.
The tectum primarily consists of the superior and inferior colliculi---clusters of neurons
that together form 4 bumps on the posterior surface of the brainstem.
The superior colliculi are thought to be involved with directing behavioral responses toward
stimuli in the environment, while the inferior colliculi are known for their role in auditory
The tegmentum contains a variety of ascending and descending tracts, like the medial lemniscus
and anterolateral tracts.
It also contains fibers from the superior cerebellar peduncles, the main output pathway
of the cerebellem, and the red nucleus---a nucleus thought to play a role in motor coordination.
The tegmentum contains nuclei for cranial nerves III and IV as well as neurons that
are part of the raphe nuclei---the major serotonin producing neurons in the brain, and the ventral
tegmental area---one of the largest collections of dopamine-producing neurons in the brain.
The basis pedunculi include the crura cerebri---two large bundles of axons that contain fibers
from motor pathways like the corticospinal and corticoblulbar tracts.
The basis pedunculi also include the substantia nigra, which is another major dopamine-producing
structure in the brain.
Finally, the area surrounding the cerebral aqueduct is called the periaqueductal gray.
The periaqueductal gray is known for its role in pain inhibition.