Anatomy of the pyramidal tract

Origin and course of pyramidal tract:
• Originates from Betz cells (in5th layer) of motor cortex –area 4
Pyramidal tract also receives fibers from supplemental motor area 6and from
parietal lobe areas1, 2, 3, 5 and 7.
• The fibers then pass through -Corona radiata,
Next through, internal capsule i.e. through genu and anterior 2/3 of
posterior limb of internal capsule, thence through
• Cerebral peduncle of midbrain–( through the middle 3/5th )and enters
• Pons –in pons the compact bundle is broken into number of small
bundles by pontine nuclei and transverse ponto cerebellar fibers and then
the tract passes on to
• upper medulla –forming again a compact tract
• In the lower medulla most of fibers of pyramidal tract decussate to
form the crossed pyramidal tract which descends in –
• The lateral column of spinal cord ;90% fibers pass through lateral column
after crossing in the lower medulla .10% fibers do not cross –descend
ipsilaterally as uncrossed fibers in anterior funicle
(Rarely all fibers cross).
Termination: axons terminate or synapse in internuncial neurons which in
turn synapse with motor cells in anterior horn cells.
 Throughout the brain stem, pyramidal tract gives out cortico bulbar fibers to
opposite side which end in nuclei of cranial nerves of opposite side.