File:Brain stem subdivisions 01.jpg

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Comparison of Old and New Brain Stem Subdivisions

Old subdivisions view of the human brain stem with the new system of segmentation revealed by developmental gene expression.


At the top, the subdivisions of the “old” human brain stem (traditional version) are based on the assumption that the midbrain extends from the thalamus to the rostral margin of the pons; this concept wrongly holds that the pretectum (dp1) and the isthmus (isth) belong to the midbrain.

At the bottom, the new segmental schema shows the “old” pons was held to extend between levels r1 to r6. In reality, r5 and r6 represent a hidden rostral retropontine part of the “medulla oblongata,” whereas the migrated basilar pons is located only within r3 and r4.

Part of the confusion relating to the extent of the pons is due to a mushroom-like rostral expansion of the pons created by rostral pontine cerebellopetal fibers that surround the trigeminal root in r2 as they approach the cerebellum in r1(see Figure 6), thus adding part of r2 to the apparent pontine bulge in humans. On the other hand, mammals with less massive pontine development than humans show a simpler, less deformed general arrangement, which leaves the ventral surface of r5 and r6 exposed.

Old version - places the pyramidal decussation (pyx) at the caudal end of the medullary brain stem, whereas the decussation actually lies in the rostral spinal cord.

The basilar pons in the human bulges rostrally into r2, where only crossed fibers of the middle cerebellar peduncle are found, and caudally, where the overhanging part of the basilar pontine nuclei partly hides the underlying rhombomeres r5 to r6 (Pn*).

The positions of the oculomotor (3N), trochlear (4N), and facial (7N) nerve nuclei, the interpeduncular nuclei (the prodromal, caudal and rostral IP parts are collectively labeled as IP*); the posterior commissure (pc), and the inferior olive are shown for reference. The rostrocaudal extent of key developmental genes is shown in the middle of the diagram. Note Fgf8 codes for the morphogen signal of the isthmic organizer, whose hindbrain gradient ends at the r1/r2 boundary.

Above text modified from original figure legend.

Se also Image - Hypothalamus model


Links: midbrain | medulla oblongata | pons | rhombomere

Reference

Watson C, Bartholomaeus C & Puelles L. (2019). Time for Radical Changes in Brain Stem Nomenclature-Applying the Lessons From Developmental Gene Patterns. Front Neuroanat , 13, 10. PMID: 30809133 DOI.


Copyright

2019 Watson, Bartholomaeus and Puelles. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.


Cite this page: Hill, M.A. (2024, June 14) Embryology Brain stem subdivisions 01.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Brain_stem_subdivisions_01.jpg

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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current13:05, 25 February 2020Thumbnail for version as of 13:05, 25 February 20201,530 × 520 (168 KB)Z8600021 (talk | contribs)==Comparison of brain stem subdivisions== the traditional view of subdivisions of the human brain stem with the new system of segmentation revealed by developmental gene expression. At the top, the subdivisions of the “old” human brain stem (the traditional version) are based on the assumption that the midbrain extends from the thalamus to the rostral margin of the pons; this concept wrongly holds that the pretectum (dp1) and the isthmus (isth) belong to the midbrain (Puelles et al., 2012a)...

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