Answers

Skeletal Muscile

#3 Muscle and tendon junction, H&E

Define a sarcomere. Be sure you know what the electron microscope has revealed about its fine structure. Know the structural changes that occur in a sarcomere during contraction and the theory that has evolved from electron microscopic studies to explain muscle contraction. A sarcomere is the basic contractile unit of a muscle cell, repeating sarcomeres comprise a myofibril. The Z-bands are considered the ends of a single sarcomere, with the H-band in the center. As the muscle contracts, the Z-bands move closer together and the I-band and H-band shorten in length as the actin thin filaments are moved along the myosin thick filaments. The A band remains the same length because the length of the myosin unit does not change.

Cardiac Muscle

#17 Heart, (Mallory-Azan)

What is the position of the nuclei? Central. Do the myofibrils pass through intercalated discs? No. How can you distinguish cross sections of cardiac muscle fibers from those of skeletal muscle fibers? Central nuclei, intercalated discs, branching fibers

Smooth Muscle

OPTIONAL: #102 Small intestine (Bodian/silver)

Note that when the muscle cells are cut in cross section, there are interruptions in the basal laminae. What is responsible for these discontinuities? Gap junctions

QUESTIONS

  1. Why do smooth muscle fibers in cross section have different diameters and why do some of these fail to show nuclei? Smooth muscle cells have tapered ends. Since the cells interdigitate different diameters would be revealed in a particular plane of section and the plane of section does not always go through the nucleus.
  2. Are myofibrils or sarcomeres present in smooth muscle fibers? No
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