Cell-cell junctions · USMLE Step 1

The 'terminal bar' observed under light microscopy at the apical end of epithelial cells most closely corresponds to which of the following under electron microscopy?

  1. A single isolated tight junction seal
  2. A single desmosome anchoring junction
  3. Tight junction, adherens junction, and desmosome together
  4. A cluster of gap junction channels only
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Correct answer: Tight junction, adherens junction, and desmosome together

The terminal bar is a light-microscope artifact representing a complex of multiple junctional structures (tight junction, adherens junction, desmosome) at the apical lateral border of epithelial cells, which can only be resolved by electron microscopy.

Difficulty: Medium Question 11 of 20

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