Hagbarth K E, Hellsing G, Löfstedt L
J Neurol Neurosurg Psychiatry. 1976 Aug;39(8):719-28. doi: 10.1136/jnnp.39.8.719.
In order to investigate myotatic reflex involvement in jaw muscle control, an analysis was made of the motor responses induced by mechanical vibration (120-160 Hz) of the jaw elevator muscles in healthy subjects. As seen in torque measurements and mean-voltage electromyographic (EMG) recordings, the vibration caused involuntary reciprocal changes in jaw muscle tone, the contraction force increasing in jaw elevators and decreasing in antagonistic jaw opening muscles. This tonic vibration reflex (TVR) elicited from the jaw elevators exhibited many characteristics similar to those previously described for limb muscle tonic vibration reflexes: it varied in strength from one subject to the next independently of the briskness of the jaw elevator tendon jerks; it had a gradual onset with successive recruitment of jaw elevator motor units firing largely out of phase with one another and at rates much lower than the vibration frequency; it was susceptible to voluntary control--when allowed visual feed-back from the torque meter all subjects were able to suppress the TVR and keep mean contraction force constant. The results indicate that with respect to the tonic motor response to sustained inflow in the Ia afferent nerve fibres, the jaw elevators do not differ markedly from other skeletal muscles. Independently of whether a TVR was present or not, the vibration caused a timing of the motor unit discharges in the jaw elevators that could not be controlled voluntarily and that showed up in gross EMG recordings as a marked grouping of discharges synchronous with each wave of vibration. A similar but less distinct grouping of the gross EMG pattern was seen in limb muscles exposed to vibration, the dispersion increasing with the peripheral conduction distances of the reflex arcs. It is suggested that contrary to the TVR, which depends on the sustained mean level of the Ia afferent input, the timing phenomenon depends, like the tendon jerk, on the degree of synchrony in the afferent Ia volleys. Monosynaptic projections may well be involved in the dynamic timing of motor discharges during tonic firing, but this does not imply that the TVR or the tonic stretch reflex is dependent upon such projections.
为了研究肌伸张反射在颌肌控制中的作用，对健康受试者颌上提肌的机械振动（120 - 160Hz）所诱发的运动反应进行了分析。从扭矩测量和平均电压肌电图（EMG）记录中可以看出，振动引起了颌肌张力的非自主交互变化，颌上提肌的收缩力增加，而拮抗的颌张开肌的收缩力降低。从颌上提肌引出的这种紧张性振动反射（TVR）表现出许多与先前描述的肢体肌肉紧张性振动反射相似的特征：其强度在不同受试者之间各不相同，与颌上提肌腱反射的活跃程度无关；它有一个逐渐开始的过程，颌上提肌运动单位相继募集，它们的放电在很大程度上彼此不同步，且放电频率远低于振动频率；它易于受到自主控制——当允许受试者从扭矩计获得视觉反馈时，所有受试者都能够抑制TVR并使平均收缩力保持恒定。结果表明，就对Ia传入神经纤维持续传入的紧张性运动反应而言，颌上提肌与其他骨骼肌没有明显差异。无论是否存在TVR，振动都会导致颌上提肌运动单位放电的时间安排无法自主控制，并且在总的EMG记录中表现为与每一波振动同步的明显放电群集。在暴露于振动的肢体肌肉中也观察到了类似但不太明显的总的EMG模式群集，随着反射弧外周传导距离的增加离散度增大。有人提出，与依赖于Ia传入输入持续平均水平的TVR相反，这种时间现象像腱反射一样，取决于传入Ia冲动的同步程度。单突触投射很可能参与了紧张性放电期间运动放电的动态时间安排，但这并不意味着TVR或紧张性牵张反射依赖于这种投射。
