Several important nuclei are located in the midbrain, including the red nuclei, the substantia nigra, and the nuclei of cranial nerves III and IV. The red nuclei connect the midbrain to the cerebellum and to the inner ear. It is also an important part of the extra pyramidal tract.he corpora quadrigemina, which is located on the posterior surface of the midbrain, is composed of two superior colliculi and two inferior colliculi. The superior colliculi are part of the visual system, relaying input from the optic tract to the lateral geniculate bodies of the thalamus.