Lev-Tov A, Tal M, Lavy R
Department of Anatomy, Hebrew University Medical School, Jerusalem, Israel.
Arch Oral Biol. 1993 Feb;38(2):169-78. doi: 10.1016/0003-9969(93)90203-x.
Microwire recordings from the histochemically heterogeneous inner compartment of the guinea pig anterior digastric muscle (ADG) revealed tonic firing of single motor units, which were spontaneously active and could also be recruited following orofacial afferent stimulation and during rhythmic jaw movements (RJM). As units with tonic firing were not observed in the homogeneously fast-twitch outer ADG, the tonic units were classified as slow-twitch motor units. Irregular patterns of motor-unit firing at variable frequencies were observed after orofacial stimulation and during RJM in the outer and inner compartments. The irregular firing pattern of units in the fast-twitch outer compartment was characterized by shorter and less variable bursts than that of units in the heterogeneous inner compartment. A phasic, centrally driven firing pattern was observed during RJM in outer and inner ADG units. The firing frequency of some of these units was modulated during the rhythmical bursts. It is suggested that, as in limb muscles, functionally specialized ADG motor units are recruited in an orderly sequence, starting with spontaneously active, slow-twitch units in the inner compartment, continuing with fast-twitch units recruited upon enhancement of the synaptic drive (as in the case of orofacial stimulation), and ending with massive, rhythmical recruitment of slow- and fast-twitch units during RJM.
对豚鼠二腹肌前腹（ADG）组织化学性质不均一的内侧肌间隔进行微丝记录，结果显示单个运动单位呈紧张性放电，这些运动单位具有自发活性，在口腔面部传入刺激后以及节律性下颌运动（RJM）期间也可被募集。由于在均一的快肌外侧ADG中未观察到紧张性放电的运动单位，因此将这些紧张性运动单位归类为慢肌运动单位。在口腔面部刺激后以及外侧和内侧肌间隔的RJM期间，观察到运动单位以不同频率进行不规则放电。快肌外侧肌间隔中运动单位的不规则放电模式的特点是，与性质不均一的内侧肌间隔中的运动单位相比，其爆发放电持续时间更短且变化更小。在外侧和内侧ADG运动单位的RJM期间，观察到一种由中枢驱动的相位性放电模式。其中一些运动单位的放电频率在节律性爆发期间受到调制。有人提出，与肢体肌肉一样，功能特化的ADG运动单位按有序顺序募集，从内侧肌间隔中具有自发活性的慢肌运动单位开始，接着是在突触驱动增强时募集的快肌运动单位（如在口腔面部刺激的情况下），最后在RJM期间大量节律性募集慢肌和快肌运动单位。
