Which statement about the terminal bar is true?

• A. It is commonly seen with light microscopy.
• B. It is most often seen in electron microscopy.
• C. It is equally visible under all microscopy methods.
• D. It cannot be seen under any microscopy.

Answer: (B)

The terminal bar represents the junctional complex at the apical border between neighboring epithelial cells, where membranes from adjacent cells come together and are linked by tight junctions and desmosomes (and related junctions). These ultrastructural features are extremely small, requiring the high resolution of electron microscopy to be seen clearly. That’s why this structure is described as being most often seen with electron microscopy—the details of the junctional apparatus are not resolvable with light microscopy, even though light microscopy can show general cell borders in some tissues. In practice, you can notice a general junctional region under light microscopy, but the precise arrangement and individual components that define the terminal bar are best observed with EM.