Document Type : Original Article
Anatomy Department, Mashhad Medical Sciences University, Mashhad, Iran
Introduction: To recognize the myelinated nerve fibers of the external capsule in human brain.
Materials and Methods: 10 adult and normal brains (20 hemispheres) from both sexes were studied using 15 mm serial sections in all three cardinal planes after fixation and processing. These sections were stained by Klüver - Barrera and Heidenhain - Woelcke methods.
Results: Some fibers from different parts of the cortex through corona radiata entered the dorsal border of the external capsule. These fibers moved ventraly and ventrocaudally toward the ventral border of the external capsule, and most of them entered the cerbral peduncles trans-, sub-, or retrolenticularly. No connection was seen between these fibers and subthalamic nucleus or substantia nigra. Some fibers passed through dorsal part of putamen and connected the external capsule with posterior limb of the internal capsule; Some fibers exchanged between the putamen and the external capsule, some of them connected the putamen with dorsal parts of the external capsule and the other fibers connected the putamen with ventral parts of the external capsule. Some fibers passed between rostrum of corpus callosum and ventral part of the external capsule. Dorsal to these fibers, there were some fibers which connected the external capsule with ventral part of accumbens nucleus. Some fibers traced from the external capsule to posterior bundle of the anterior commissure; some of them entered the commissure but others terminated in nucleus basalis (Meynert) neurons. Some fibers passed through rostral part of the external capsule and connected the frontal lobe with medial dorsal nucleus of thalamus.
Conclusion: The external capsule is a part of the white matter of the cerebral hemisphere which contains different variety of nerve bundles. The main component of the external capsule is the corticotegmental fibers, especialy in dorsal parts. This capsule provides very important pathways for connecting the cortex to subcortical nuclei as well as the different cortical areas with each others.