Morphology and physiology of masticatory muscle motor units.

T. Eijden, S. Turkawski
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引用次数: 105

Abstract

Motor unit territories in masticatory muscles appear to be smaller than territories in limb muscles, and this would suggest a more localized organization of motor control in masticatory muscles. Motor unit cross-sectional areas show a wide range of values, which explains the large variability of motor unit force output. The proportion of motor unit muscle fibers containing more than one myosin heavy-chain (MHC) isoform is considerably larger in masticatory muscles than in limb and trunk muscles. This explains the continuous range of contraction speeds found in masticatory muscle motor units. Hence, in masticatory muscles, a finer gradation of force and contraction speeds is possible than in limb and in trunk muscles. The proportion of slow-type motor units is relatively large in deep and anterior masticatory muscle regions, whereas more fast-type units are more common in the superficial and posterior muscle regions. Muscle portions with a high proportion of slow-type motor units are better equipped for a finer control of muscle force and a larger resistance to fatigue during chewing and biting than muscle portions with a high proportion of fast units. For the force modulation, masticatory muscles rely mostly on recruitment gradation at low force levels and on rate gradation at high force levels. Henneman's principle of an orderly recruitment of motor units has also been reported for various masticatory muscles. The presence of localized motor unit territories and task-specific motor unit activity facilitates differential control of separate muscle portions. This gives the masticatory muscles the capacity of producing a large diversity of mechanical actions. In this review, the properties of masticatory muscle motor units are discussed.
咀嚼肌运动单元的形态学和生理学。
咀嚼肌的运动单元区域似乎比肢体肌肉的区域小,这可能表明咀嚼肌的运动控制组织更局部。运动单元横截面积显示的值范围很广,这解释了运动单元力输出的大变异性。咀嚼肌中含有多于一种肌球蛋白重链(MHC)亚型的运动单位肌纤维的比例比四肢和躯干肌肉大得多。这解释了咀嚼肌运动单元收缩速度的连续范围。因此,咀嚼肌的力和收缩速度可能比四肢和躯干肌肉更精细。慢速型运动单元在咀嚼肌深层和前区所占比例较大,而快速型运动单元在咀嚼肌浅部和后区所占比例较多。拥有高比例慢速运动单元的肌肉部位,在咀嚼和咬咬过程中,能够更好地控制肌肉力量,并且比拥有高比例快速运动单元的肌肉部位具有更大的抗疲劳能力。咀嚼肌的力调节主要依靠低力水平时的招募梯度和高力水平时的速率梯度。Henneman的运动单元有序募集原则也被报道用于各种咀嚼肌。局部运动单元区域和特定任务运动单元活动的存在促进了对不同肌肉部分的差异控制。这赋予了咀嚼肌产生多种机械动作的能力。本文就咀嚼肌运动单元的特性作一综述。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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