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Cerebellar relation to muscle spindles in hand tracking

Elsevier Science & Technology
DOI: 10.1016/s0079-6123(08)63416-0
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Publisher Summary The cautionary warning raise on the limb studies is, whether each eye movement is indeed governed separately from all others, or whether all are affected through a differential control of a common neural element, such as the muscle spindle and the stretch reflexes. The limb and the eye are similar in their capacity to move in planned trajectories. To do this, the central processes that control the two members must face similar problems in selecting the muscles, force, direction, position (and its time derivatives), and times of initiation and termination that are needed to program a trajectory. Yet, the limb and the eye are very different in many respects and the question is whether any of the differences creates special control problems unique to one member. One such difference is the tendency of the limb to oscillate. Reasons for believing that one normal function of the intact cerebellar dentate and interposed nuclei is the control of the oscillation through adjustment of stretch reflexes are: 1) in precise ramp tracking, these cerebellar neurons do not relate to parameters of trajectory; 2) in precise ramp tracking, these cerebellar neurons do relate to spindle afferent discharge as though controlling it or being controlled by it, or both; 3) in precise ramp tracking, the one parameter of movement that these cerebellar neurons obviously monitor is tremor; 4) oscillation is itself a problem inherent in the design of the normal neuromusculoskeletal system; and 5) tremor is itself a normal phenomenon that may be kept within acceptable limits, but never prevented entirely.

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