Skeletal or Striated Muscle

The most characteristic features of skeletal muscle are large, multinucleate fibers with cross-striations.

Examine the musculature of the larynx (slide 7) using low power and study its organization into fascicles.

• Identify epimysium and perimysium.
• With the 40X objective, examine muscle fibers cut in transverse and in longitudinal section and identify endomysium and blood vessels of various sizes (Figs. 10-3 and 10-4).

Where are the nuclei of these muscle fibers located? Nuclei of what three cell types are located just outside the muscle fibers?

Clinical note: Exercise or increased use of specific muscles produce hypertrophy or increased fiber size, while disuse results in muscle atrophy. One form of the hereditary disease muscular dystrophy, in which fibers do not mature properly or survive, results from a defect in the gene for dystrophin, a large protein with poorly understood functions located just inside the sarcolemma.

Examine the striations on longitudinally cut fibers, comparing them with Figs. 10-7 and 10-8.

• Identify A bands and I bands and
• Be sure you understand what these bands represent in terms of sarcoplasmic organization (Figs. 10-8 through 10-12).

Based on the diagrams of Fig. 10-12, would you say the muscle on slide 7 was relaxed or contracted when it was fixed? Why?

Examine the transversely cut fibers on slide 7 again. Try to distinguish individual myofibrils. Compare what you see to the EMs and the diagram in Fig. 10-8.

Draw what the myofilament arrangement in a sarcomere cross-section would most likely be in a relaxed muscle.

Electron microscopic images