Padykula H A, Gauthier G F
J Cell Biol. 1970 Jul;46(1):27-41. doi: 10.1083/jcb.46.1.27.
Distinct ultrastructural differences exist at the neuromuscular junctions of red, white, and intermediate fibers of a mammalian twitch skeletal muscle (albino rat diaphragm). The primary criteria for recognizing the three fiber types are differences in fiber diameter, mitochondrial content, and width of the Z line. In the red fiber the neuromuscular relationship presents the least sarcoplasmic and axoplasmic surface at each contact. Points of contact are relatively discrete and separate, and axonal terminals are small and elliptical. The junctional folds are relatively shallow, sparse, and irregular in arrangement. Axoplasmic vesicles are moderate in number, and sarcoplasmic vesicles are sparse. In the white fiber long, flat axonal terminals present considerable axoplasmic surface. Vast sarcoplasmic surface area is created by long, branching, closely spaced junctional folds that may merge with folds at adjacent contacts to occupy a more continuous and widespread area. Axoplasmic and sarcoplasmic vesicles are numerous. Both axoplasmic and sarcoplasmic mitochondria of the white fiber usually contain intramitochondrial granules. The intermediate fiber has large axonal terminals that are associated with the most widely spaced and deepest junctional folds. In all three fiber types, the junctional sarcoplasm is rich in free ribosomes, cisternae of granular endoplasmic reticulum, and randomly distributed microtubules.
在哺乳动物单收缩骨骼肌（白化大鼠膈肌）的红色、白色和中间型肌纤维的神经肌肉接头处，存在明显的超微结构差异。识别这三种纤维类型的主要标准是纤维直径、线粒体含量和Z线宽度的差异。在红色肌纤维中，神经肌肉关系在每次接触时呈现出最少的肌浆和轴浆表面。接触点相对离散且分开，轴突终末小且呈椭圆形。连接褶相对较浅、稀疏且排列不规则。轴浆小泡数量适中，肌浆小泡稀疏。在白色肌纤维中，长而扁平的轴突终末呈现出相当大的轴浆表面。长而分支、紧密排列的连接褶形成了巨大的肌浆表面积，这些连接褶可能与相邻接触处的褶合并，占据更连续和广泛的区域。轴浆和肌浆小泡数量众多。白色肌纤维的轴浆和肌浆线粒体通常含有线粒体内颗粒。中间型肌纤维具有大的轴突终末，与间隔最宽、最深的连接褶相关联。在所有三种纤维类型中，连接肌浆富含游离核糖体、颗粒内质网的池和随机分布的微管。
