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Show f. C!in. NeUfll-pphth.l/nllll. 2: 28~-284, 1l182. NORMA BOSCHETTI BARTON, MD., PhD. RONALD G. CLARK, PhD. Thi~ ~peein1t'n i~ unique in th.lt it .lliows the \·i~1I.1Iiz.lti''I1"f.1Il.1t'llllie.ll ~tnl(ture~ at the inferior ~urf.Ke llf the br.lin n)upled tl) .1 uo~~ ~eetion of the Illidbr.lin .It the level ,)f the inferior colliculus. The f,)urth nerve~ (.Hwwhe.ld~) de(Uss.lte at the ~ureri,)r medul\.lry velum ("SIllV") dors.ll to the cerebr.ll .1lJueduct (".1"). The nerves exit at the dl)r~.ll surbce d the br.lin stem caudal to the inferior cl)lIiculus ("IC'). The midbrJin can be divided into the tectum •Ind the (erebrJI peduncles. The tectum consists of the superior Jnd inferior colliculi ("Sc. IC'). The cerebral peduncles .:Ire further subdivided into a dorsal portion, the tegmentum. and the crura cerebri ("C'). The cerebral aqueduct ("a") separates the tectum from the tegmentum. This separation is more obvious in sections of the midbrain which are higher than the one shown. The substantia nigra ("SN") separates the tegmentum from the crurJ cerebri. The superior colliculus receives afferents from the retina, cerebral cortex, inferior colliculus, and spinal cord. Although most fibers in the optic tract ("OT") terminate in the lateral geniculate body ("LG"), a small number project to the superior colliculus and to the pretectal area via the brachium of the superior colliculus ("bs"). The pretectal area is located rostral to the superior colliculus and is the principal midbrain center involved in the pup- From the DepJrtment of Ophth.llm,.lol(Y (NBBI. B.ls,,>m r.llnll'r Eve Institute. Unlv"",tv of Mi.lml School of Medi,'ine, Mi.lmi. Florid.l; .lnd the Dep",iment l>f An.llomy (Ree). Universitv l>f Ml.lmi SlhooJ of Medlline, Mi.lmi. r1"ndJ. December 1982 Neuro-anatomicaI Feature Photo illary light reflex. The efferents of the superior colliculus are to the pulvinar ("P") and posterior th.ll,lmUs; it is involved in the coordination of head .lnd eye movements in response to visual and auditory stimuli. The inferior colliculus is involved in acoustic reflexes, and its efferents project to the medial geniculate body ("Me"). The cerebral aqueduct, which has a triangular appearance in cross section, is surrounded by a central gray area (the periaqueductal gray- "pg"). At the periphery of this zone, there is a network of fibers and cells-the reticular formation. The white area occupying the central portion of the tegmentum is the decussation of the superior cerebral peduncle ("dec"). This is the largest bundle of cerebellar efferents projecting to the thalamus. The substantia nigra extends throughout the midbrain and caudal diencephalon. It is a large nuclear mass intimately related to the basal ganglia, namely the caudate and putamen. It is the principal source of dopamine and is implied in the metabolic disturbances of Parkinsonsim. The crus cerebri ("C') is a massive bundle of corticofugal fibers: corticospinal, corticopontine, and the corticobulbar. Between the crura is the interpeduncular fossa. The mammillary bodies and the ventral aspect of the hypothalamus lie in the fossa. The tuber cinereum ("TC") lies posterior to the chiasm ("Ch"). From the anterior portion of the tuber cinereum the infundibulum of the pituitary gbnd arises (not shown). Write t,'r reprint;; I,,: N,lrnM B'lschetli B.uton. M.D.. B.1swm r.11mer Eye Institute. l100 N. W. 17th Street. P.O. Box IO()880, Mi.1mi, F1orid.1 ~JIOI. 283 21\4 Journal of Clinical Neuro-ophthalmology |
