PHYSIOLOGY AND PHARMACOLOGY OF EXTRAOCULAR MUSCLES

眼外肌（EOM）在哺乳动物中是独特的，因为它们含有两个 纤维的主要群体：单神经支配（SIF）和倍增 神经支配（MIF）。 肢体肌肉中没有MIF。 两种纤维类型 又分为两层： 轨道和全球。 我们的长远目标是探索 EOM纤维的生理和形态特性，希望 建立眼运动的细胞基础。 形态学研究 表明眼眶MIF显示两种类型神经接头。 相同的 纤维具有单个终板，该终板终止于纤维的中心部分， 纤维和众多的，小的和表面的结束集中在 远端区域。 肌浆网的发育发生显著变化 从纤维的中心区域，在那里它是发达的，到 在稀疏的远端部分。 这些观察提示 纤维生理特性的相应差异可 存在于这两个区域之间。 产生动作电位的能力 在这两个领域将得到检验。 快与慢的分布 肌球蛋白和不同的ATP酶，沿着纤维将被研究。 的 失神经支配对眼外肌纤维电特性的影响将是 考察 纤维的神经再支配过程也将被研究 以确定其是否特定于纤维类型。 代谢 MIF产生的张力要求将通过以下方式进行研究： 分析不同代谢抑制剂的效果。 的作用 细胞外Ca ~（2+）在MIF兴奋-收缩偶联机制中作用 将被探索。 将研究无钙盐水和 降低Cr的试剂增加膜对Ca（Cd和Ca）的渗透性， 硝苯地平;硝酸盐和硫氰酸盐）。 功能性变化， 眼外肌在出生后早期发育过程中所经历的 分析了 SIF和MIF的结构将被连续地检查 横截面，重点是末端的位置和外观， 线粒体和肌浆网的分布。 为此目的，将采用形态测量技术。

Extraocular muscles (EOM's) are unique in mammales because they contain two main populations of fibers: singly innervated (SIF's) and multiply innervated (MIF's). MIF's are absent in limb muscles. The two fiber types have been subdivided into several categories distributed in two layers: orbital and global. Our long term objective is to explore the physiological and morphological properties of EOM fibers with the hope of establishing the cellular basis of ocular motility. Morphological studies indicate that orbital MIF's display two types of nerve junctions. The same fiber has a single endplate ending localized in the central portion of the fiber and numerous, small and superficial endings concentrated in the distal region. The development of sarcoplasmic reticulum markedly changes from the central region of the fiber, where it is well developed, to the distal portion where it is sparse. These observations suggest that corresponding differences in the physiological properties of the fiber may exist between these two regions. The ability to generate action potential in these two areas will be tested. The distribution of fast and slow myosins and different ATPases, along the fiber will be studied. The effects of denervation on the electrical properties of EOM fibers will be examined. The process of reinnervation of fibers also will be investigated to determine whether it is specific for fiber type. The metabolic requirements of the tension produced by MIF's will be investigated by analyzing the effects of different metabolic inhibitors. The role of extracellular Ca in the excitation-contractin coupling mechanism of MIF's will be explored. The effects will be studied of Ca-free salines and of agents that decrease cr increase membranes permeability to Ca (Cd and nifedipine; nitrate and thiocyanate). The functional changes that extraocular muscles undergo in early postnatal development will be analyzed. The structure of SIF's and MIF's will be examined in serial cross-sections with emphasis on the location and appearance of endings and on the distribution of mitochondria and sarcoplasmic reticulum. Morphometirc techniques will be employed for this purpose.