title: Intermuscular and intramuscular differences in myosin heavy chain composition of the human masticatory muscles.
abstract: Among and within the human masticatory muscles a large number of anatomical differences exists indicating that different muscles and muscle portions are specialized for certain functions. In the present study we investigated whether such a specialization is also reflected by intermuscular and intramuscular differences in fibre type composition and fibre cross-sectional area. Fibre type compositions and fibre cross-sectional areas of masticatory muscles were determined in eight cadavers using monoclonal antibodies against myosin heavy chain (MyHC). The temporalis, masseter and pterygoid muscles could be characterized by a relatively large number of fibres containing more than one MyHC isoform (hybrid fibres). In these muscles a large number of fibres expressed MyHC-I, MyHC-fetal and MyHC-cardiac alpha. Furthermore, in these muscles type I fibres had larger cross-sectional areas than type II fibres. In contrast, the mylohyoid, geniohyoid and digastric muscle were characterized by less hybrid fibres, and by less fibres expressing MyHC-I, MyHC-fetal, and MyHC-cardiac alpha, and by more fibres expressing MyHC-IIA; the cross-sectional areas of type I and type II fibres in these muscles did not differ significantly. Compared to the masseter and pterygoid muscles, the temporalis had significantly larger fibres and a notably different fibre type composition. The mylohyoid, geniohyoid, and digastric muscles did not differ significantly in their MyHC composition and fibre cross-sectional areas. Also intramuscular differences in fibre type composition were present, i.e., a regionally higher proportion of MyHC type I fibres was found in the anterior temporalis, the deep masseter, and the anterior medial pterygoid muscle portions; furthermore, significant differences were found between the bellies of the digastric.
authors.affiliation: Department of Functional Anatomy, Academic Centre for Dentistry Amsterdam (ACTA), Meibergdreef 15, 1105 AZ, Amsterdam, The Netherlands. j.a.korfage@amc.uva.nl
authors.forename: J A
authors.initials: JA
authors.lastname: Korfage
authors.forename: P
authors.initials: P
authors.lastname: Brugman
authors.forename: T M
authors.initials: TM
authors.lastname: Van Eijden
mesh_terms: D000368:Aged; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000737:chemistry; D008410:Masticatory Muscles / Q000737:chemistry* / Q000166:cytology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry*; D018995:Myosin Heavy Chains / Q000032:analysis*; D009426:Netherlands; D020033:Protein Isoforms / Q000032:analysis; D011626:Pterygoid Muscles / Q000737:chemistry; D044465:White People
chemical_list: D020033:Protein Isoforms; D018995:Myosin Heavy Chains