In 1940 Sommer1 observed that the Jendrassik maneuver which is used to reinforce the human tendon jerk was ineffectual when the muscle afferents were instead stimulated electrically according to the technique of Hoffmann (H reflex). Both the mechanically evoked and the H reflex share a pathway that includes muscle spindle stretch receptor axons, a predominantly monosynaptic coupling with motoneurons for the same muscle, and a final path to the muscle over motor axons. In addition the tendon jerk requires the activation of the stretch receptor end-organs in the muscle, while the electric stimulus short-circuits this portion of the physiological system. Since the Jendrassik maneuver did not augment the H reflex, Sommer inferred that the potentiation could not take place at the common central motoneuron synapse, but must instead occur peripherally at the stretch end-organ which is part of the tendon jerk circuit. He postulated that activity in the motor neurons
LANDAU WM, CLARE MH. Fusimotor Function: Part IV. Reinforcement of the H Reflex in Normal Subjects. Arch Neurol. 1964;10(2):117–122. doi:10.1001/archneur.1964.00460140003001
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