PERSISTANCE DE CARACTERES ONTOGÉNIQUES DANS LE MUSCLE MASSÉTER ADULTE
During embryonic and foetal development, the masseter is formed from two successive generations of muscle fibers in a manner which is very similar to that which has been previously described for other skeletal muscles. This phenotype
is characterised by the persisten ce of ontogenic myosin isoforms ( embryonic and foetal myosin heavy chains, embryonic light chain) and by the presence of two distinct populations of fibers : small diameter fibers which coexpress the
embryonic, foetal and fast isoforms of the myosin heavy chains but never express the slow isoform; large diameter fibers which express the slow myosin heavy chain either exclusively or in variable associations with the other isoforms.
These characteristics of the human masseter muscle probably correspond not only to its embryological origin and its special innervation, but also to the functional constraints to which it is submitted after birth.
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