Miles T S, Nordstrom M A, Türker K S
J Physiol. 1986 Jan;370:457-65. doi: 10.1113/jphysiol.1986.sp015944.
Action potentials of single motor units in the human masseter muscle were recorded during isometric contractions at different muscle lengths over most of the working range of the temporomandibular articulation. The shape of the unit potential wave form changed progressively as the muscle length changed. This was considered to be due principally to a change in the geometric relationship of the electrode to the muscle fibres at various muscle lengths. The recruitment thresholds for all units increased sharply when the jaw opening approached the maximal gape. The pattern of change of unit thresholds with muscle length closely paralleled the curve of length versus passive tension for the combined jaw-closing muscles, temporomandibular articulation and associated soft tissues. It was concluded that the change in unit recruitment thresholds with length is likely to be a consequence of the length-passive tension relationship of the muscles, joint and soft tissues. The results of this study indicate that attempts to assign masseter motor units to one or other of the accepted functional categories on the basis of recruitment force or wave form only are unlikely to give reliable results.
在颞下颌关节的大部分工作范围内，于不同肌肉长度的等长收缩过程中记录了人类咬肌单个运动单位的动作电位。随着肌肉长度的变化，单位电位波形的形状逐渐改变。这主要被认为是由于在不同肌肉长度下电极与肌纤维的几何关系发生了变化。当张口接近最大开口度时，所有单位的募集阈值急剧增加。单位阈值随肌肉长度的变化模式与联合闭口肌、颞下颌关节及相关软组织的长度与被动张力曲线密切平行。得出的结论是，单位募集阈值随长度的变化很可能是肌肉、关节和软组织的长度 - 被动张力关系的结果。本研究结果表明，仅基于募集力或波形试图将咬肌运动单位归入一种或其他公认的功能类别不太可能得出可靠结果。
