Department of Odontology, Clinical Oral Physiology, Umeå University, Sweden.
Anat Rec (Hoboken). 2011 Jul;294(7):1158-69. doi: 10.1002/ar.21272. Epub 2011 Jun 1.
The human jaw system is different from those of other primates, carnivores, ruminants, and rodents in temporomandibular joint and muscle anatomy. In adults, jaw muscles also differ markedly from limb and trunk muscles in composition and distribution of fibre types. It can be assumed that age-related changes between young age to adulthood in terms of craniofacial growth, teeth eruption, and improvement of jaw functions are paralleled by alterations also in composition and distribution of jaw muscle fibre types. To address this question, we have examined the fibre type composition of the human masseter, a jaw closing muscle, at young age. For comparison, the young biceps brachii was examined. The results were compared with previous data for adult masseter and biceps muscles. Young masseter and biceps were similar in that type I fibres outnumbered other fibre types and were of the same diameter. However, they differed in composition of other fibre types. Young masseter contained fibre types I, IM, IIC, IIAB, IIB, and scarce IIA, with regional differences, whereas young biceps showed types I, IIA, IIAB, and few IIB. Young masseter differed from young biceps also by smaller type II fibre diameter and by containing fetal MyHC. In addition, the masseter and biceps differed in age-related changes of composition and distribution of fibre types between young age and adulthood. We conclude that the human masseter is specialized in fibre types already at young age and shows a unique fibre type growth pattern, in concordance with being a separate allotype of muscle.
人类的颌系统在颞下颌关节和肌肉解剖结构上与其他灵长类动物、食肉动物、反刍动物和啮齿动物不同。在成年人中，颌部肌肉在组成和纤维类型分布上也与四肢和躯干肌肉明显不同。可以假设，从幼年到成年，颅面生长、牙齿萌出和颌功能改善方面的年龄相关变化与颌部肌肉纤维类型的组成和分布变化相平行。为了解决这个问题，我们检查了年轻时期人类咬肌（一种颌闭合肌肉）的纤维类型组成。为了比较，还检查了年轻的肱二头肌。结果与成人咬肌和肱二头肌的先前数据进行了比较。年轻的咬肌和肱二头肌在纤维 I 型数量多于其他纤维类型且直径相同方面相似。然而，它们在其他纤维类型的组成上有所不同。年轻的咬肌包含纤维 I、IM、IIC、IIAB、IIB 和稀少的 IIA，具有区域性差异，而年轻的肱二头肌显示出纤维 I、IIA、IIAB 和少量的 IIB。年轻的咬肌还与年轻的肱二头肌在纤维 II 直径较小以及包含胎儿 MyHC 方面存在差异。此外，咬肌和肱二头肌在年轻时期到成年期之间的纤维类型组成和分布的年龄相关变化方面也存在差异。我们得出结论，人类咬肌在年轻时期就已经具有专门的纤维类型，并表现出独特的纤维类型生长模式，与作为一种单独的肌肉同种型相一致。
