Neuromechanics of Differential Motor Unit Activation in Multifunctional Muscles

描述(申请人提供)：肌肉中运动单位的招募通常被理解为按照固定的顺序从施加小力量的单位到施加大力量的单位进行。然而，这种理解在文献中受到了质疑，因为研究表明，一些肌肉中的运动单位因关节力的不同方向而被不同地招募。然而，运动单位的差异激活的生理学基础尚未建立。以第一背侧骨间肌(FDI)作为多功能肌的模型，我们将确定FDI内不同的运动单位是否以不同的外展与屈曲力的比例施加抽动力。如果不同的运动单位在一个方向上比另一个方向有更大的机械优势，我们将确定中枢神经系统(CMS)是否激活运动单位，以便在给定任务中具有最大机械优势的单位优先被激活。中风后受影响的手失去方向控制可能与运动单位的选择性激活崩溃有关，导致食指力量的某些方向无法获得或无法控制。我们的研究将通过寻求在未受损的人类受试者中建立差异运动单位激活的生理学基础来确定这一假说的可行性。我们将使用尖峰触发平均(STA)来评估运动单位抽动力方向。尽管STA不能准确地估计抽动的绝对幅度，但它可以准确地确定运动单位抽动力的方向。我们将检查不同定向任务中抽动方向的STA估计的一致性。通过对许多电机单元的研究，我们将评估外国直接投资电机单元可以产生的抽动方向的分布。我们将确定运动单位的抽动方向与其招募之间是否存在相关性。我们的研究既将确定STA是否是运动单位抽动力方向的可靠指标，也将确定运动单位之间不同的抽动力方向是否构成差异运动单位激活的生理基础。与公共卫生相关：中风后，许多人失去了向特定方向移动关节的能力。我们的研究既寻求开发方法来检查脊髓中单个细胞控制的运动方向，又试图确定未受损的大脑如何激活这些细胞来控制关节运动的不同方向。拥有这些信息将为我们提供一个基线，然后我们可以用它来更好地了解受损的大脑如何控制脊髓，以及特定的干预措施如何改善中风后的运动控制。

DESCRIPTION (provided by applicant): The recruitment of motor units in a muscle is generally understood to progress in a fixed order from units that exert small forces to units that exert large forces. However, this understanding has been questioned in the literature as studies have shown that motor units in some muscles are recruited differently for different directions of joint force. However, the physiological basis for the differential activation of motor units has not been established. Using the first dorsal interosseous (FDI) as a model multifunctional muscle, we will determine if different motor units within the FDI exert twitch forces with different ratios of abduction to flexion force. If different motor units have a greater mechanical advantage for one direction over another, we will determine if the central nervous system (CMS) activates motor units so that units with the greatest mechanical advantage for the given task are preferentially activated. Loss of directional control in the affected hand after stroke may relate to a breakdown in the selective activation of motor units rendering some directions of index finger force either inaccessible or uncontrollable. Our study will determine the feasibility of this hypothesis by seeking to establish the physiological basis of differential motor unit activation in unimpaired human subjects. We will assess motor unit twitch force direction using spike- triggered averaging (STA). STA may accurately determine motor unit twitch force direction despite the fact that it can not accurately estimate the absolute amplitude of a twitch. We will examine the consistency of STA estimates for twitch direction across different directional tasks. By studying many motor units, we will assess the distribution of twitch directions that can be generated by FDI motor units. We will determine if a correlation exists between the twitch direction of a motor unit and its recruitment. Our study will both determine whether STA is a reliable indicator of motor unit twitch force direction, and determine whether different twitch force directions among motor units forms the physiological basis for differential motor unit activation. Relevance to Public Health: After suffering a stroke, many individuals lose the ability to move their joints in particular directions. Our study seeks both to develop methods to examine the direction of movement controlled by single cells in the spinal cord, and to determine how the undamaged brain activates these cells to control different directions of joint movement. Having this information will give us a baseline which we can then use to better understand how the damaged brain controls the spinal cord, and how specific interventions may improve motor control post-stroke.