SEM Based Determination of the Motor to Sensory Axon Ratio of the Lateral & Medial Roots of the Median Nerve
This study of the human brachial plexus quantifies and compares the total number of axons, axon diameter, and axon density within the lateral and medial roots of the median nerve in twenty-seven adult human cadavers (IRB Ref #1030 V.0). The lateral and medial cords give rise to the lateral and medial roots, which join to form the median nerve. Increased understanding of axon quantity, axon diameter, and axon density is critical in the case of brachial plexus root injury. The ratios of motor to sensory fibers present in the lateral and medial roots of the median nerve of the brachial plexus were investigated. Peripheral nervous tissue sections of the lateral and medial roots were surgically removed from the axilla region of formalin-fixed cadavers. Excised tissue sections were fractured using liquid nitrogen-based freeze-cracking, and subsequently viewed using scanning electron microscopy. ImageJ 1.x and Microsoft Excel software were used to analyze axon count, diameter, and density, plus fascicular bundle count. Results revealed a higher ratio of sensory to motor fibers for the lateral root, and a higher ratio of motor to sensory fibers for the medial root. Analysis of the fiber composition of the roots that form the median nerve is important for predicting potential functional implications of injury. Our data suggests different patterns of motor and sensory losses in the upper extremity following injury of the upper or lower roots of the brachial plexus involving the median nerve.
Walters, B.N., Brandt, L.S.E., and Kunigelis, S.C. (2023). SEM Based Determination of the Motor to Sensory Fiber Ratio of the Lateral & Medial Roots of the Median Nerve.