Fig. 15. Electron micrograph of a twitch fiber in human extraocular muscle. This fiber shows less development of the sarcoplasmic reticulum and T system than the cell in Figure 17. Mitochondria occur in rows between the myofibrils. This cell would be classified as a “red” twitch fiber. The diagram below the electron micrograph shows how the filaments produce the banding pattern. (Courtesy of Dr. T. Iwamoto.)