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Invited review: Microneurography and applications to issues of motor control: Fifth annual stuart reiner memorial lecture
Author(s) -
Hagbarth KarlErik
Publication year - 1993
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880160702
Subject(s) - microneurography , motor control , neuroscience , medicine , physical medicine and rehabilitation , psychology , baroreflex , heart rate , blood pressure
Among the hypotheses regarding fusimotor functions based on earlier animal experiments some are inconsistent, others are in conformity with microneurographic observations in man. The human data provide evidence against the following two theories: (1) the length follow‐up servo theory; and (2) the theory that fusimotor neurons can be selectively activated to produce spindle sensitization and stretch reflex reinforcements. The human data support the theory of alpha–gamma coactivation. In particular, in the early phase of isometric voluntary contractions fusimotor‐driven afferent spindle activity assists in autogenetic activation of alpha motoneurons and in reciprocal relaxation of antagonists. As muscle fatigue develops, the autogenetic reflex drive via the fusimotor route declines. The fusimotor bias during contraction provides for maintenance of spindle sensitivity to minute perturbations and for load‐compensating reflex adjustments to such perturbations. Reflex overcorrections may lead to uncontrollable oscillations of the type seen in enhanced physiological tremor.