Rowlerson A, Mascarello F, Barker D, Saed H
Department of Physiology, Glasgow University, UK.
J Anat. 1988 Dec;161:37-60.
The various parts of the masseter muscle complex (pars superficialis, pars profunda, zygomaticomandibularis, maxillomandibularis) in the rat, guinea-pig, rabbit, cat and macaque monkey were examined to discover whether they showed any relationship between the distribution of muscle spindles and extrafusal fibre types. Intrafusal (spindle) and extrafusal fibre types in masseter were compared with those in limb muscles and were identified by a combination of standard histochemical methods and indirect immunoperoxidase staining with antibodies specific for the various isoforms of myosin characteristic of fibre types in mammalian muscle. In general, the fibre-type properties of intrafusal fibres in masseter resembled those in limb muscle spindles, but the extrafusal fibre-type composition was unlike that in most limb muscles. In the rat masseter, most of the spindles were clustered together in a few very restricted areas. Extensive fusion of the external capsules of adjacent spindles, resulting in the formation of giant spindles, was seen in the cat and monkey masseter; this was sometimes accompanied by the enclosure of extrafusal fibres within the fused spindles. Common to all species, but strongest of all in the rat, was a close association between the distributions of muscle spindles and extrafusal Type I (slow twitch) fibres within the masseter complex. Muscle spindles and Type I fibres were either absent or rarest in the superficial part of masseter, but were most common in the deep layer (pars profunda) or zygomaticomandibularis. The functional significance of these observations is discussed.
对大鼠、豚鼠、兔子、猫和猕猴的咬肌复合体各部分（浅层部分、深层部分、颧下颌肌、上颌下颌肌）进行了检查，以确定它们在肌梭分布与梭外肌纤维类型之间是否存在任何关系。将咬肌中的梭内（肌梭）和梭外肌纤维类型与肢体肌肉中的进行比较，并通过标准组织化学方法和间接免疫过氧化物酶染色相结合的方式进行鉴定，使用针对哺乳动物肌肉中纤维类型特有的各种肌球蛋白同工型的特异性抗体。一般来说，咬肌中梭内纤维的纤维类型特性与肢体肌肉肌梭中的相似，但梭外纤维类型组成与大多数肢体肌肉不同。在大鼠咬肌中，大多数肌梭聚集在少数非常有限的区域。在猫和猕猴的咬肌中可以看到相邻肌梭的外膜广泛融合，形成巨大肌梭；这有时伴随着融合肌梭内包含梭外纤维。所有物种都有一个共同特点，在大鼠中最为明显，即咬肌复合体内肌梭分布与梭外I型（慢肌纤维）纤维之间存在密切关联。肌梭和I型纤维在咬肌浅层要么不存在，要么最为稀少，但在深层（深层部分）或颧下颌肌中最为常见。讨论了这些观察结果的功能意义。
