This review examines kinetic properties and distribution of the 11 isoforms of myosin heavy chain (MyHC) expressed in extraocular muscle (EOM) fibre types and the regulation and function of these MyHCs. Although recruitment and discharge characteristics of ocular motoneurons during fixation and eye movements are well documented, work directly linking these properties with motor unit contractile speed and MyHC composition is lacking. Recruitment of motor units according to Henneman's size principle has some support in EOMs but needs consolidation. Both neurogenic and myogenic mechanisms regulate MyHC expression as in other muscle allotypes. Developmentally, multiply‐innervated (MIFs) and singly‐innervated fibres (SIFs) are derived presumably from distinct myoblast lineages, ending up expressing MyHCs in the slow and fast ends of the kinetic spectrum respectively. They modulate the synaptic inputs of their motoneurons through different retrogradely transported neurotrophins, thereby specifying their tonic and phasic impulse patterns. Immunohistochemical analyses of EOMs regenerating in situ and in limb muscle beds suggest that the very impulse patterns driving various ocular movements equip effectors with appropriate MyHC compositions and speeds to accomplish their tasks. These experiments also suggest that satellite cells of SIFs and MIFs are distinct lineages expressing different MyHCs during regeneration. MyHC compositions and functional characteristics of orbital fibres show longitudinal variations that facilitate linear ocular rotation during saccades. Palisade endings on global MIFs are postulated to respond to active and passive tensions by triggering axon reflexes that play important roles during fixation, saccades and vergence. How EOMs implement Listings law during ocular rotation is discussed.

中文翻译：

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眼外肌纤维中的肌球蛋白重链：分布、调节和功能。

本综述检查了在眼外肌 (EOM) 纤维类型中表达的肌球蛋白重链 (MyHC) 的 11 种异构体的动力学特性和分布，以及这些 MyHC 的调节和功能。尽管在注视和眼球运动期间眼运动神经元的募集和放电特征有据可查，但缺乏将这些特性与运动单元收缩速度和 MyHC 组成直接联系起来的工作。根据 Henneman 的大小原则招募运动单位在 EOM 中有一些支持，但需要整合。神经源性和肌源性机制都像在其他肌肉同种异型中一样调节 MyHC 的表达。在发育上，多神经支配 (MIF) 和单神经支配纤维 (SIF) 可能来自不同的成肌细胞谱系，最终分别在动力学谱的慢端和快端表达 MyHC。它们通过不同的逆行运输的神经营养因子调节运动神经元的突触输入，从而指定它们的强直和相位脉冲模式。对原位和四肢肌肉床再生的 EOM 的免疫组织化学分析表明，驱动各种眼球运动的脉冲模式使效应器具有适当的 MyHC 成分和速度来完成它们的任务。这些实验还表明 SIF 和 MIF 的卫星细胞是不同的谱系，在再生过程中表达不同的 MyHC。眼眶纤维的 MyHC 成分和功能特征显示出纵向变化，有助于在扫视期间进行线性眼球旋转。全球 MIF 上的栅栏末端被假定通过触发轴突反射来响应主动和被动张力，轴突反射在固定、眼跳和聚散期间发挥重要作用。讨论了 EOM 如何在眼球旋转期间实施 Listings 定律。