Why do the nerve tracts decussate? Basic principles of the vertebrate brain organization

Authors: R. Bartoš *1,2;  D. Ospalík 3;  A. Hejčl 1;  A. Malucelli 1;  M. Sameš 1;  V. Němcová *2
Authors‘ workplace: Veronika Němcová a Robert Bartoš, se na minimonografii podíleli stejným, dílem. *;  Neurochirurgická klinika UJEP, Masarykova, nemocnice, KZ a. s., Ústí nad, Labem 1;  Anatomický ústav 1. LF UK, Praha 2;  Neurologické oddělení, Masarykova, nemocnice, KZ a. s., Ústí nad Labem 3
Published in: Cesk Slov Neurol N 2021; 84/117(4): 316-328
Category: Minimonography
doi: 10.48095/cccsnn2021316


The fact that some brain tracts decussate accompanies medical students and neurologists and neurosurgeons during the whole period of their study, as well as in their work “careers”. We take the decussation of the pyramidal tract, anterolateral, lemniscal systems and visual pathways for granted and we describe contralateral hemipareses, hemiplegia, including alternating ones, Brown-Séquard’s spinal cord hemisyndrome and homonymous hemianopsia. We understand the central lesion of the facial nerve, presenting only with contralateral paresis of mouth muscles while the ability to close the eye is preserved. The other tracts which cross and in which we do not often realize this are for example the tracts of the dentate-rubro-olivary (Guillain-Mollaret’s) triangle, lemniscus lateralis (corpus trapezoideum) conducting hearing, tractus pontocerebellaris, and tractus dentatothalamicus (decussatio pedunculi cerebellaris superioris). The trochlear nerve, tectospinal tract (decussatio tegmenti dorsalis) and rubrospinal tract (decussation tegmenti ventralis) decussate in the mesencephalon, reticulospinal tracts are both crossed and also uncrossed and on the contrary the crossing of the interstitiospinal tract from the ncl. of Cajal and vestibulospinal tract from the ncl. of. Dieters are not present. We questioned this finding, so we conducted the review of the pertinent literature concerning the theories why the tracts cross, we added the mnemotechnic predator theory of the silur sea, and we concentrated on the phylogenetic differences in the architecture of vertebrate brains, with the help of dissection of brain cadavers from rabbit (Oryctolagus cuniculus), duck (Anas platyrhynchos domesticus) and carp (Cyprinus carpio). Based on our results, we are not able to answer all of the above-mentioned and further related questions, hence we present them to the reader in the form of a minimonography.


brain tract – comparative anatomy – Nervous system – corticospinal tract – optic chiasm – evolution


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