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nmdcat.online July 28, 2026

A histologist observing a muscle tissue slide notes the presence of centrally located, single nuclei within branched cells that are joined by specialized dark-staining regions. The primary functional significance of these specialized regions is to:

A. Anchor actin filaments during contraction
B. Prevent overstretching of the muscle fibers
C. Allow rapid spread of depolarization between cells
✓
D. Store calcium ions for muscle contraction

📝 Explanation

The tissue described is cardiac muscle. The specialized dark-staining regions are intercalated discs, which contain gap junctions. These gap junctions allow ions to pass freely between cells, facilitating the rapid spread of depolarization so the heart can contract as a functional syncytium.

📖 Additional Information

  • Anchor actin filaments during contraction
  • Prevent overstretching of the muscle fibers
  • Allow rapid spread of depolarization between cells
  • Store calcium ions for muscle contraction

The tissue described is cardiac muscle. The specialized dark-staining regions are intercalated discs, which contain gap junctions. These gap junctions allow ions to pass freely between cells, facilitating the rapid spread of depolarization so the heart can contract as a functional syncytium.

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During a laboratory experiment, a tissue sample is placed in a calcium-free extracellular fluid. Upon electrical stimulation, the tissue completely fails to contract, whereas another tissue sample continues to contract for a short period before failing. The first tissue most likely belongs to which type of muscle?

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