Decussation of the pyramids

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Brain: Decussation of the pyramids
Deep dissection of brain-stem. Lateral view. ("pyramidal tract" visible in red, and "pyramidal decussation" labeled at lower right.)
Latin	decussatio pyramidum
Gray's	subject #192 870
NeuroNames	hier-796
Dorlands/Elsevier	d_04/12282126

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.

[edit] Additional images

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

[edit] External links

• pyramidal+decussation at eMedicine Dictionary
• 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 As such, some of the information contained herein may be outdated.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.

v • d • e Brain: rhombencephalon (hindbrain) Metencephalon/ pons Dorsal/ (tegmentum) surface: Locus ceruleus Trigeminal lemniscus (Dorsal trigeminal tract, Ventral trigeminal tract) cranial nuclei: GSA: Principal V/Spinal V - VIII-c (Dorsal, Anterior)/VIII-v (Lateral, Superior, Medial, Inferior) - SVE: Motor V - VII - GSE: VI - GVE: VII: Superior salivary nucleus MLF, III, IV and VI (vestibulo-oculomotor fibers, medial vestibulospinal tract) sensory/ascending: Trapezoid body/VIII - Superior olivary nucleus Inferior cerebellar peduncle (Vestibulocerebellar tract) motor/descending: Apneustic center • Pneumotaxic center (Medial parabrachial nucleus) - Lateral parabrachial nucleus Ventral/ (base) Middle cerebellar peduncles (Pontocerebellar fibers) - Pontine nuclei motor/descending: Corticospinal tract - Corticobulbar tract - Corticopontine fibers Raphe/reticular Reticular formation (Caudal, Oral, Tegmental, Paramedian) • Raphe nuclei (Median) Myelencephalon/ medulla Dorsal surface: Posterior median sulcus - Postero-lateral sulcus - Area postrema cranial nuclei: GVA: VII,IX,X: Solitary/tract • SVA: Gustatory nucleus • GSE: XII  • GVE: IX,X,XI: Ambiguus • SVE: X: Dorsal • IX: Inferior salivatory nucleus - MLF, III, IV and VI sensory/ascending: Gracile nucleus • Cuneate nucleus (Accessory cuneate nucleus) • Sensory decussation  • Medial lemniscus motor/descending: Dorsal respiratory group Ventral motor/descending: Ventral respiratory group - Pyramid (Motor decussation) - Inferior olivary nucleus (Olivocerebellar tract, Rubro-olivary tract) surface: Anterior median fissure - Antero-lateral sulcus - Arcuate nucleus of medulla - Olivary body Raphe/reticular Reticular formation (Gigantocellular, Parvocellular, Ventral, Lateral, Paramedian) • Raphe nuclei (Obscurus, Magnus, Pallidus)