Final answer:
The sarcoplasm, being the cytoplasm of muscle cells that contains numerous fibrils, makes up most of the volume of a typical myocyte.
Step-by-step explanation:
The majority of a typical myocyte's volume is composed of the sarcoplasm, which is the cytoplasm of muscle cells. The sarcoplasm contains numerous fibrils resulting in the striated appearance of the muscle. The sarcomere is the contractile unit within these fibrils, composed of actin and myosin proteins. The sarcomere itself does not comprise the majority of the muscle cell's volume. Similarly, while the sarcoplasmic reticulum plays a critical role in muscle contraction through the storage, release, and retrieval of calcium ions, it does not constitute the main volume of the cell. Lastly, the sarcolemma is the plasma membrane that encloses the muscle cell but is not responsible for the majority of the cell's volume.