Skeletal muscles are precisely structured arrays of actin and myosin, and several additional proteins that ensure proper muscle organization and contraction. A recent paper looked at the roles of tropomodulin in skeletal muscle, and found that in the absence of one tropomodulin, two other tropomodulins were able to preserve correct muscle morphology but not correct muscle function. Image above shows a transmission electron micrograph of normal muscle.
Reference: David S. Gokhin, Raymond A. Lewis, Caroline R. McKeown, Roberta B. Nowak, Nancy E. Kim, Ryan S. Littlefield, Richard L. Lieber, and Velia M. Fowler, 2010. Originally published in Journal of Cell Bioloy. doi: 10.1083/jcb.201001125. Paper can be found here.