8 to 15 weeks of age , showed that at the age of 8 weeks the myocardiocytes are poorly differentiated cells : they contain microfilaments of actin and myosin inserted on the cytoplasmic aspect of plasmalemma , a smooth endoplasmic reticulin and mitochondria , accounting for the early contraction .
C0010834
cytoplasmic
C0007603
plasmalemma