Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0040822 (tremor)
 18,428 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By taking into account the torque/angle and the torque/angular speed relationships of antagonist muscles acting across a joint it is possible to predict the contraction dynamics when they are simultaneously activated at a constant level. The simulation is displayed in a "phase-plane" where trajectories for each starting condition (angle--abscissa, angular speed--ordinate) represent the contraction dynamics. The results vary in the position of attractors, repulsors and trajectory shapes. Attractor points (at zero speed) have particular significance in joint stabilization. It was found that with certain reciprocal torque/angle relationships of antagonist muscles, a range of stable joint angles can be quickly reached just by selecting the proper group activation level. A given ratio between the activation levels selects the stable joint angle (attractor) while the overall amplitude will set the joint stiffness in that position. Thus a hypothesized control system should choose just two neural activation amplitudes (time-course considerations are unnecessary), with a reduction of the information needed to stiffen the joint. Furthermore, even ignoring the effects of joint friction, the trajectories toward attractors showed a tendency to cross the zero speed boundary no more than once, resembling the behaviour of an overdamped spring-dashpot system. A couple of testing simulations demonstrated that the combination of non-linear torque/angle and torque/speed relationships is essential to avoid tremor-like paths about the equilibrium and to quickly stiffen the joint. Other aspects related to co-contractions are discussed in the paper.
 ...
PMID:Contraction dynamics in antagonist muscles. 796 21

Reflex sympathetic dystrophy (RSD) is a neuropathic pain condition most often occurring in relation to trauma to, or surgery on, an extremity. It is characterized among other things by motor disturbances such as joint stiffness and tremor. Signs and symptoms can be induced in a rat model through chronic constriction of a sciatic nerve (CCI-model). In this study the CCI-model was used to evaluate the extent of bilateral peripheral motor nerve-fiber involvement in relation to ligature localization. In 12 Lewis rats, the common sciatic nerve was loosely ligated with four chromic catgut ligatures at the midthigh level just proximal to the right sciatic trifurcation. Acetylcholinesterase (CE) histochemistry of sciatic (distal and proximal to ligation) and corresponding contralateral nerve biopsy specimens was performed at 21 days after ligation. An additional 12 rats were sham-operated and served as controls. As compared to sham-operated controls or contralateral nonligated sciatic nerves, CE histochemistry after 21 days revealed a marked decrease of CE-positive fibers in cross-sections taken from distal and proximal sciatic nerve biopsies ipsilateral to the ligatures. In addition, as compared to sham-operated controls, there was a decrease of CE-positive fibers in cross-sections taken from contralateral nonligated sciatic nerves. The present findings indicate profound motor denervation, distal as well as proximal to the ligatures. Motor denervation also affected the contralateral nonligated sciatic nerve. The evident usefulness of the CCI-model for the study of RSD places the present results in line with the concept of central nervous system involvement in the pathophysiology of RSD.
 ...
PMID:Motor dysfunction and reflex sympathetic dystrophy. Bilateral motor denervation in an experimental model. 968 64

Active or passive movement causes a temporary reduction in muscle stiffness that gradually returns to baseline levels when the muscle remains still. This effect, termed muscle thixotropy, alters the mechanical properties of the joint around which the muscle acts, reducing its resonant frequency. Because physiological tremor is affected by joint mechanics, this suggests that prior movement may alter tremor independently of neural output. To address this possibility, vertical acceleration of the outstretched prone hand was recorded in eight healthy subjects, along with EMG activity of the extensor digitorum communis muscle. A series of voluntary wrist flexion/extension movements was performed every 20 s, interspersed by periods during which hand position was maintained. Time-dependent changes in the amplitude and frequency of acceleration and EMG were analyzed using a continuous wavelet transform. Immediately following movement, acceleration displayed a significant increase in wavelet power accompanied by a reduction in peak frequency. During the postmovement period, power declined by 63%, and frequency increased from 7.2 to 8.0 Hz. These changes occurred with an exponential time constant of 2-4 s, consistent with a thixotropic mechanism. In contrast to acceleration, EMG activity showed no significant changes despite being strongly related to acceleration during the movement itself. These results show that prior movement transiently increases the amplitude and reduces the frequency of physiological tremor, despite unchanging neural output. This effect is best explained by a reduction in joint stiffness caused by muscle thixotropy, highlighting the importance of mechanical factors in the genesis of physiological tremor.
 ...
PMID:Postmovement changes in the frequency and amplitude of physiological tremor despite unchanged neural output. 2066 Apr 21