The difference pattern of regulation by muscle spindles during the various cortically-induced rhythmic movements

经验表明，在精神压力下，骨骼肌张力增加，无意识地引起咬牙、磨牙等功能异常，这表明口颌系统与精神状态之间存在密切关系。因此，在本研究中，我们研究了精神应激对口颌系统的影响以及咬合夹板的影响。健康的成年志愿者参与了这项研究。以2小时的字母识别任务作为应激源。记录颞肌和咬肌肌的肌电图、食指掌面和前额的排汗率、食指掌面皮肤血流量、咬肌局部肌肉氧合情况。心率谱分析评估自主神经功能。采用两种不同硬度的咬合夹板。在脑力任务中，咬肌和颞肌的综合肌电活动、组织血红蛋白O_2饱和度（StO_2）和Lo/Hi比值（交感神经活动的标志）较脑力任务前有所增加。这些增加在至少30到60分钟后具有统计学意义；之后没有发现明显的变化。综合皮肤血流量和排汗没有明显变化。软性夹板增加了颞肌电综合活动和Lo/Hi比值，而硬性夹板没有增加。这些结果表明，咬合夹板的硬度可以影响咀嚼肌活动和自主神经系统活动在应激条件下。

It has been known empirically that under mental stress, skeletal muscle tone is increased and parafunction such as clenching or teeth grinding can be caused unconsciously, which suggests that a close relationship exists between the stomatognathic system and the mental condition. In this study, therefore, we investigated what the effect of mental stress on the stomatognathic system is and what the effect of occlusal splints is.Healthy adult volunteers participated in this study. A letter identification task over a 2-hour period was employed as a stressor. Electromyographic records were taken from the temporal and masseteric muscles, sweat rates from the palmar surface of index finger and from forehead, skin blood flow from the palmar surface of index finger, local muscle oxygenation from the masseter muscle. Assessment of autonomic function was made by heart rate spectral analysis. Two occlusal splints of different hardness were employed.During the mental task, the integrated EMG activity of masseteric and temporal muscles, tissue hemoglobin O_2 saturation (StO_2), and the Lo/Hi ratio (a marker of sympathetic activity) increased as compared before the mental task. These increases were statistically significant after at least 30 to 60 minutes ; afterwards no notable changes were found. The integrated skin blood flow and sweat expulsion did not change significantly. The integrated temporal EMG activity and Lo/Hi ratio increased with the soft splint, but did not with the hard splint. These results indicate that the hardness of an occlusal splint can affect the masticatory muscle activity and autonomic nervous system activity under stressful conditions.