Sarcoplasm is the cytoplasm of a myocyte (muscle fiber). It is comparable to the cytoplasm of other cells, but it contains unusually large amounts of glycosomes (granules of stored glycogen) and significant amounts of myoglobin, an oxygen-binding protein. The calcium ion concentration in sarcoplasma is also a special element of the muscle fiber; it is the means by which the muscle contractions take place and are regulated.