Cross Section Through the Inferior Colliculi of the Midbrain

Cross Section Through the Inferior Colliculi of the Midbrain

The inferior colliculus with its nucleus (nucleus of inferior colliculus) (D14) (synaptic relay station of the central auditory path-way) is seen dorsally. The transitional re-gion between pons and cerebral peduncles and the most caudal cell groups of the sub-stantia nigra (D15) lie ventrally. The magno-cellular nucleus of the trochlear nerve (D16) is clearly visible in the center of the teg-mentum below the aqueduct, and the lateroposterior tegmental nucleus (D17) issituated dorsal to it. Further lateral are the cells of the locus ceruleus (D18) (the pontine respiratory center reaching into the mid-brain; it contains noradrenergic neurons, p. 100, B28). The relatively large, scattered cells dorsal to the locus ceruleus form the mesencephalic nucleus of the trigeminal nerve (D19). The lateral field is occupied bythe pedunculopontine tegmental nucleus (D20). At the ventral margin of the tegmen-tum lies the interpeduncular nucleus (D21), which is rich in peptidergic neurons (pre-dominantly enkephalin). The habenulo in-terpeduncular tract (fasciculus retroflexus,Meynert’s bundle), which de-scends from the habenular nucleus, termi-nates here.

The lateral lemniscus (D22) radiates ven-trally into the nucleus of the inferior col-liculus (D14). The fibers of the peduncle of the inferior colliculus (D23)aggregate at the lateral aspect and run to the medial geniculate body (central auditorypathway, p. 378). In the medial field lie the medial longitudinal fasciculus (D24) and the decussation of the superior cerebellarpeduncle (D25). The fiber plateof the medial lemniscus (D26) lies laterally. The fibers of the cerebral peduncle (D27) are cut transversely and are inter-spersed with a few pontine fibers running across.

D28 Periaqueductal gray substance,centralgray.

C29 Edinger – Westphal nucleus (accessorynucleus of the oculomotor nerve).