Decussation of the pyramids

Brain: Decussation of the pyramids
Deep dissection of brain-stem. Lateral view. ("pyramidal tract" visible in red, and "pyramidal decussation" labeled at lower right.)
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Latin	decussatio pyramidum
Gray's	subject #192 870
Part of
Components
Artery
Vein
BrainInfo/UW	hier-796
MeSH	[1]

The two pyramids contain the motor fibers that pass from the brain to the medulla oblongata and medulla spinalis, corticobulbar and corticospinal fibers.

When these pyramidal fibers are traced downward, it is found that some two-thirds or more of them leave the pyramids in successive bundles, and decussate in the anterior median fissure of the medulla oblongata, forming what is termed the pyramidal decussation.

Having crossed the middle line, they pass down in the posterior part of the lateral funiculus as the lateral cerebrospinal fasciculus.

Additional images

Gray663.png

Diagrams of the medulla spinalis.

Medulla oblongata and pons. Anterior surface.

Decussation of pyramids. Scheme showing passage of various fasciculi from medulla spinalis to medulla oblongata.

Section of the medulla oblongata through the lower part of the decussation of the pyramids

Section of the medulla oblongata at the level of the decussation of the pyramids.

Superficial dissection of brain-stem. Ventral view.

The motor tract.

Human brain frontal (coronal) section description 2.JPG

Human brain frontal (coronal) section

External links

• Dictionary at eMedicine pyramidal+decussation
• Anatomy Atlases - Microscopic Anatomy, plate 17.326 - "Medula Oblongata"

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.