Luff A R, Proske U
Am J Physiol. 1979 Jan;236(1):C35-40. doi: 10.1152/ajpcell.1979.236.1.C35.
The tension developed by single motor units of the iliofibularis muscle of the frog Litoria aurea was recorded in response to single-shock and repetitive stimulation of motor axons. The majority of units in each muscle, 13 on the average, were of the twitch type; an additional 4 units were slow or tonic. It appeared that slow units comprised a single homogeneous population, but two types of twitch units could be recognized: small fatigue-resistant units with long twitch times to peak (20--40 ms) and larger, fatigable units with briefer times to peak (16--27 ms). Evidence from a comparison of unit tetanic tensions indicated the presence of polyneuronal innervation of both slow and twitch muscle fibers. The relatively low incidence of polyneuronal innervation of twitch fibers in iliofibularis, when compared with a muscle like sartorius (9), was attributed to the difference in lengths of muscle fibers in the two muscles. It was argued that slow muscle fibers probably receive a multiterminal as well as polyneuronal innervation, with the terminals of any one axon lying widely spaced along the muscle fiber.
记录了金色树蛙（Litoria aurea）髂腓肌单个运动单位在对运动轴突进行单脉冲刺激和重复刺激时所产生的张力。每块肌肉中的大多数单位，平均为13个，属于快肌纤维类型；另外还有4个单位是慢肌纤维或紧张性肌纤维。看起来慢肌纤维单位构成了一个单一的同质群体，但可以识别出两种类型的快肌纤维单位：一种是抗疲劳的小单位，达到峰值的收缩时间较长（20 - 40毫秒），另一种是较大的、易疲劳的单位，达到峰值的时间较短（16 - 27毫秒）。对单位强直张力的比较证据表明，慢肌纤维和快肌纤维都存在多神经元支配。与缝匠肌等肌肉相比，髂腓肌中快肌纤维多神经元支配的发生率相对较低（9），这归因于两块肌肉中肌纤维长度的差异。有人认为，慢肌纤维可能同时接受多终末和多神经元支配，任何一条轴突的终末沿肌纤维广泛分布。
