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Gallasch, E; Rafolt, D; Kenner, T; Konev, A; Kozlovskaya, IB.
Physiological tremor and control of limb position in 1 and 0 G.
J Gravit Physiol. 1994; 1(1): P52-P54.
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Leading authors Med Uni Graz: Gallasch Eugen
Co-authors Med Uni Graz: Kenner Thomas
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Abstract:: Muscle and skeletal mechanoreceptors play an important role for the regulation of muscular tone and the genesis of normal Physiological Tremor (PT). For example if a big limb as the arm or leg is kept against the gravity vector, the la afferent spindle discharges continuously control the load bearing flexor in a negative feedback manner in order to compensate the gravity vector and to the stabilize arm position. This servo-like action, denoted as 'stretch reflex', not only increases static postural stability (tonic stretch reflex) but also counteracts against external disturbances by dynamically increasing the muscle tone. Muscle spindles are very sophisticated sensory organs. They have an own innervation and the endings of the nuclear bag fibres are highly sensitive for small microstretches. EMG and microneurografic studies showed their importance in the mechanism of the 8-12 Hz component for PT. In a 0 G a limb becomes position controlled. In contrast to 1g, where control of limb position is a subordinated function of force compensation in the load bearing muscle, an antagonistic control scheme is necessary in 0 G to compensate the arm against positional drifts. As a consequence there is a shift from load dependent (muscular) to position dependent (skeletal) mechanoreceptors that become involved in the neural control process. As the control process is reflected in the tremor pattern, we investigated arm tremor in a constant limb position in 1 and 0 G.
Find related publications in this database (using NLM MeSH Indexing): Arm - physiology; Gravitation - physiology; Humans - physiology; Leg - physiology; Mechanoreceptors - physiology; Muscle Contraction - physiology; Muscle Spindles - physiology; Muscle Tonus - physiology; Neuromuscular Junction - physiology; Proprioception - physiology; Psychomotor Performance - physiology; Space Flight - physiology; Tremor - etiology; Weightlessness - etiology