Thomas, Juergen E.

Measurements of conduction velocity of the motor fibers of the ulnar nerve in the segment between the upper part of the arm and the wrist were made in 6 premature infants, 42 full-term newborn infants and 98 children up through the age of 14 years. In premature infants, 21 – 40 days before full term, values ranged from 18 to 22 meters per second with a mean of 21. Full-term newborn infants had velocities that ranged from 21 to 33 m.p.s., with a mean of 28. The values in the newborn were about one-half those of normal young adults, which range from 47 to 73 m.p.s. (mean, 60). By the age of 3 years almost all values were in the lower part of the adult range and, at 5 years, the velocities were not significantly different from those of the adult. These observations are in harmony with information about the diameter of nerve fibers during growth in man. The H-reflex could be elicited by stimulation of the ulnar nerve in almost every newborn infant. By the age of 1 year and thereafter it could rarely be elicited. Between the elbow and wrist, afferent fibers subserving this reflex conducted with a mean velocity of 30 m.p.s. Data on the action potential of the hypothenar muscles, residual latency of conduction in the ulnar nerve, latency of the H-reflex and conduction in the peroneal nerve in infants and children are compared with those on adults. Submitted on July 15, 1959