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February 1964

Fusimotor Function: Part V. Reflex Reinforcement Under Fusimotor Block in Normal Subjects

Author Affiliations

From the Department of Neurology and the Beaumont-May Institute of Neurology, Washington University School of Medicine.

Arch Neurol. 1964;10(2):123-127. doi:10.1001/archneur.1964.00460140009002

In the previous study 1 we have been unable to confirm the finding of Sommer2 and others3,4 that the H reflex in man is not subject to reinforcement in the same manner as the tendon jerk. Nevertheless it remains possible that the efferents to muscle spindle stretch receptors are an essential link in the pathway for the Jendrassik phenomenon. In animals our present knowledge of the gamma efferent fibers to striated muscle has evolved from techniques where ventral root, dorsal root, or muscle nerve fibers are dissected and recorded separately. Such techniques are hardly applicable in man.

The motor fibers to extrafusal muscle fibers as well as the afferents from muscle spindles and tendon receptors are the largestdiameter myelinated nerve fibers, largely in the alpha range, while the fusimotor fibers are predominantly in the small myelinated gamma group. This circumstance provides an approach to funcional study, for the