The brachial plexus is formed from five spinal roots: C5, C6, C7, C8 and T1, providing innervation to the upper limb. It has been shown that the morphometric analysis of nerve fibers is of great value in detecting abnormalities, such as the size of nerve bundles, the number or size of axons and the area of myelin. The present study was performed on samples of 10 brachial plexuses (5 right, 5 left), obtained from 5 fresh cadavers, male, with an average age between 24 ± 3.14 (range, 20-30 years), and 73 ± 5.52 years (range, 60-90 years), with no history of malignancy and neuropsychiatric pathology. The samples were fixed in 10% formalin and stained with hematoxylin- eosin. The data obtained from the 10 brachial plexuses were grouped into two age ranges, these being young and adult. In the group of young people the number of fascicles in C5, 4.00 ± 1.22; C6, 9.25 ± 3.83; C7, 15.20 ± 7.57; C8, 8.60 ± 5.39; T1, 4.80 ± 3.19 in adults the diameter of the root was C5, 4.77 ± 1.31; C6, 5.39 ± 0.76; C7, 5.91 ± 1.63; C8, 5.19 ± 0.94; T1, 4.86 ± 1.40. There are differences between the nerve roots of the human brachial plexus, young individuals and Chilean adults, so the root area of young individuals is smaller, the number of fascicles decreases in adult individuals and their diameters are always higher in the latter.

KEY WORDS: Brachial plexus; Estate; Morphometry