<P> In contrast to this argument for a single origin of muscle cells , Steinmetz et al. argue that molecular markers such as the myosin II protein used to determine this single origin of striated muscle actually predate the formation of muscle cells . This author uses an example of the contractile elements present in the porifera or sponges that do truly lack this striated muscle containing this protein . Furthermore , Steinmetz et al. present evidence for a polyphyletic origin of striated muscle cell development through their analysis of morphological and molecular markers that are present in bilaterians and absent in cnidarians , ctenophores , and bilaterians . Steimetz et al. showed that the traditional morphological and regulatory markers such as actin , the ability to couple myosin side chains phosphorylation to higher concentrations of the positive concentrations of calcium , and other MyHC elements are present in all metazoans not just the organisms that have been shown to have muscle cells . Thus , the usage of any of these structural or regulatory elements in determining whether or not the muscle cells of the cnidarians and ctenophores are similar enough to the muscle cells of the bilaterians to confirm a single lineage is questionable according to Steinmetz et al. Furthermore , Steinmetz et al. explain that the orthologues of the MyHc genes that have been used to hypothesize the origin of striated muscle occurred through a gene duplication event that predates the first true muscle cells ( meaning striated muscle ) , and they show that the MyHc genes are present in the sponges that have contractile elements but no true muscle cells . Furthermore , Steinmetz et all showed that the localization of this duplicated set of genes that serve both the function of facilitating the formation of striated muscle genes and cell regulation and movement genes were already separated into striated myhc and non-muscle myhc . This separation of the duplicated set of genes is shown through the localization of the striated myhc to the contractile vacuole in sponges while the non-muscle myhc was more diffusely expressed during developmental cell shape and change . Steinmetz et al. found a similar pattern of localization in cnidarians with except with the cnidarian N. vectensis having this striated muscle marker present in the smooth muscle of the digestive track . Thus , Steinmetz et al. argue that the pleisiomorphic trait of the separated orthologues of myhc can not be used to determine the monophylogeny of muscle , and additionally argue that the presence of a striated muscle marker in the smooth muscle of this cnidarian shows a fundamentally different mechanism of muscle cell development and structure in cnidarians . </P>
<P> In contrast to this argument for a single origin of muscle cells , Steinmetz et al. argue that molecular markers such as the myosin II protein used to determine this single origin of striated muscle actually predate the formation of muscle cells . This author uses an example of the contractile elements present in the porifera or sponges that do truly lack this striated muscle containing this protein . Furthermore , Steinmetz et al. present evidence for a polyphyletic origin of striated muscle cell development through their analysis of morphological and molecular markers that are present in bilaterians and absent in cnidarians , ctenophores , and bilaterians . Steimetz et al. showed that the traditional morphological and regulatory markers such as actin , the ability to couple myosin side chains phosphorylation to higher concentrations of the positive concentrations of calcium , and other MyHC elements are present in all metazoans not just the organisms that have been shown to have muscle cells . Thus , the usage of any of these structural or regulatory elements in determining whether or not the muscle cells of the cnidarians and ctenophores are similar enough to the muscle cells of the bilaterians to confirm a single lineage is questionable according to Steinmetz et al. Furthermore , Steinmetz et al. explain that the orthologues of the MyHc genes that have been used to hypothesize the origin of striated muscle occurred through a gene duplication event that predates the first true muscle cells ( meaning striated muscle ) , and they show that the MyHc genes are present in the sponges that have contractile elements but no true muscle cells . Furthermore , Steinmetz et all showed that the localization of this duplicated set of genes that serve both the function of facilitating the formation of striated muscle genes and cell regulation and movement genes were already separated into striated myhc and non-muscle myhc . This separation of the duplicated set of genes is shown through the localization of the striated myhc to the contractile vacuole in sponges while the non-muscle myhc was more diffusely expressed during developmental cell shape and change . Steinmetz et al. found a similar pattern of localization in cnidarians with except with the cnidarian N. vectensis having this striated muscle marker present in the smooth muscle of the digestive track . Thus , Steinmetz et al. argue that the pleisiomorphic trait of the separated orthologues of myhc can not be used to determine the monophylogeny of muscle , and additionally argue that the presence of a striated muscle marker in the smooth muscle of this cnidarian shows a fundamentally different mechanism of muscle cell development and structure in cnidarians . </P>
what type of muscle is the digestive system
what type of muscle is the digestive system
smooth
smooth