Thermographic analysis of the mechanism of involuntary contraction of the facial mimic muscles

面部模仿肌肉是自愿或反射性收缩的。虽然这些肌肉由快肌纤维和慢肌纤维组成，但它们缺乏通常诱导慢肌纤维反射收缩所需的内在肌梭。我们发现，位于提上睑肌和睑板之间的Mueller肌的机械感受器作为外源性机械感受器引起面部慢缩纤维的反射性收缩。为了强烈地收缩上眼睑，提上睑肌非骨骼肌快缩纤维的增加的自主收缩拉伸Mueller肌中的机械感受器以强烈地唤起三叉神经本体感受。这种本体感受刺激面部运动神经元，通过中脑三叉神经元和蓝斑诱发面部慢缩纤维的反射性收缩，两者都与缝隙连接相连。面部慢缩纤维的这种反射性收缩通过热成像产生热量。

Facial mimic muscles are contracted voluntarily or reflexively. Although these muscle consist of fast- and slow-twitch fibers, they lack intrinsic muscle spindles normally required to induce reflex contraction of slow-twitch fibers. We found that the mechanoreceptors in Mueller's muscle, which locates between the levator muscle and the tarsus, function as extrinsic mechanoreceptors to induce reflex contraction of the facial slow-twitch fibers. To strongly retract the upper eyelid, increased voluntary contraction of the levator non-skeletal fast-twitch fibers stretches the mechanoreceptors in Mueller's muscle to strongly evoke trigeminal proprioception. This proprioception stimulates the facial motor neurons to induce reflex contraction of the facial slow-twitch fibers via the mesencephalic trigeminal neurons and the locus ceruleus, both of which are connected with gap junctions. This reflex contraction of the facial slow-twitch fibers thermographically produces heat.