Motor-Unit Architecture in Long Parallel-Fibered Muscles

描述（由申请人提供）：本研究的长期目标是了解不同人体肌肉运动单元的结构和行为。运动单元是神经肌肉系统的基本功能单元。肌肉纤维组织成运动单元的方式和运动单元活动的协调方式是肌肉产生力量和运动能力的重要决定因素。本提案的重点是调查运动单位的组织和协调在长，平行纤维的人体肌肉。这些肌肉中的纤维通常被认为横跨整个肌肉。然而，初步的研究支持这样一种观点，即一些肌肉，包括肱桡肌，可能有一个复杂的结构，由一系列排列在长纤维支架上的短纤维阵列组成。一些较长的纤维在广泛分离的终板区接受来自多个运动神经元的神经支配。串联纤维组织成运动单元的方式，以及这些运动单元如何协调以有效地将力传递给肌腱的方式尚不清楚。本研究将通过以下具体目的来探讨这些问题：(1)确定肱桡肌的神经支配模式；(2)确定肱桡肌运动单元的组织方式；(3)阐明肱桡肌不同近端和远端运动单元的协调策略；(4)确定多神经支配的纤维是否存在于其他长的、平行纤维的肌肉中，包括肱二头肌、缝匠肌、股薄肌和背阔肌。将使用一种新的电生理方法。肌电图信号将记录在自愿收缩期间使用多个细线和针电极。这些信号将被分解以识别单个运动单元的动作电位。运动单元的结构特性，包括终板位置和纤维长度，将通过分析动作电位波形来估计，运动单元的控制特性，包括招募和同步，以及多神经支配纤维的存在将通过分析运动单元的放电模式来确定。这项工作将有助于了解特定人类肌肉的结构和功能，这将直接关系到几个临床应用，包括肌腱转移和重建手术，功能电刺激，神经学和运动学肌电图，以及治疗性运动。

DESCRIPTION (provided by applicant): The long-term goal of this research is to understand the architecture and behavior of motor units in different human muscles. The motor unit is the basic functional unit of the neuromuscular system. The way muscle fibers are organized into motor units and the way motor unit activity is coordinated are important determinants of a muscle's ability to produce force and movement. The focus of this proposal is to investigate motor-unit organization and coordination in long, parallel-fibered human muscles. The fibers in these muscles are often assumed to span the entire length of the muscle. However, preliminary work supports the idea that some muscles, including brachioradialis, may instead have a complex architecture, consisting of arrays of shorter fibers arranged in series over a scaffolding of longer fibers. Some of the longer fibers receive innervation from more than one motoneuron at widely separated endplate zones. The way in which in-series fibers are organized into motor units, and the way these motor units are coordinated to transfer force effectively to the tendon are not known. The proposed study will investigate these issues through the following specific aims: (1) determining the innervation pattern in brachioradialis; (2) determining how motor units in brachioradialis are organized; (3) elucidating the strategy used to coordinate motor units at different proximodistal levels in brachioradialis; and (4) determining whether polyneuronally innervated fibers exist in other long, parallel-fibered muscles, including brachial biceps, sartorius, gracilis, and latissimus dorsi. A novel electrophysiological approach will be used. Electromyographic signals will be recorded during voluntary contractions using multiple fine-wire and needle electrodes. The signals will be decomposed to identify individual motor-unit action potentials. Motor-unit architectural properties, including endplate locations and fiber lengths, will be estimated by analyzing the action-potential waveforms, Motor-unit control properties, including recruitment and synchronization, and the existence of polyneuronally innervated fibers will be determined by analyzing the motor-unit discharge patterns. The proposed work will contribute knowledge about the structure and function of particular human muscles which will be directly relevant to several clinical applications, including tendon-transfer and reconstructive surgery, functional electrical stimulation, neurological and kinesiological electromyography, and therapeutic exercise.