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nmdcat.online July 28, 2026

Under equilibrium conditions, a specific muscle type maintains a state of partial contraction known as “muscle tone” or “tonus” in the walls of hollow organs. The characteristic feature of this muscle type at the cellular level is:

A. The presence of distinct A and I bands
B. The alignment of Z-lines to form striations
C. The arrangement of actin and myosin in a lattice-like diagonal network
✓
D. The extensive development of the sarcoplasmic reticulum

📝 Explanation

The muscle maintaining tonus in hollow organs is smooth muscle. Unlike striated muscles, smooth muscle lacks distinct A and I bands and Z-lines. Instead, actin and myosin filaments are arranged in a diagonal, lattice-like network anchored to dense bodies.

📖 Additional Information

  • The presence of distinct A and I bands
  • The alignment of Z-lines to form striations
  • The arrangement of actin and myosin in a lattice-like diagonal network
  • The extensive development of the sarcoplasmic reticulum

The muscle maintaining tonus in hollow organs is smooth muscle. Unlike striated muscles, smooth muscle lacks distinct A and I bands and Z-lines. Instead, actin and myosin filaments are arranged in a diagonal, lattice-like network anchored to dense bodies.

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