Where are gap junctions typically NOT located?

Gap junctions are specialized intercellular connections that facilitate direct communication between adjacent cells by allowing the passage of ions and small molecules. They play an essential role in coordinating activities among cells, particularly in tissues that require synchronized function, such as cardiac muscle and some smooth muscle.

In the heart, gap junctions are abundant and are crucial for the rapid transmission of electrical signals, enabling coordinated heart contractions. Similarly, in cardiac muscle, these junctions facilitate the spread of action potentials across the myocardial tissue, ensuring that the heart beats in unison.

In skeletal muscle, however, gap junctions are not typically found. Instead, skeletal muscle cells are innervated by motor neurons, and muscle contraction is primarily regulated through neuromuscular junctions rather than direct cell-to-cell communication via gap junctions.

The cornea, while being an avascular tissue, does have a unique type of cellular organization that includes gap junctions, facilitating communication between epithelial cells. Therefore, the presence of gap junctions is expected in the heart and some other muscle types, but not in skeletal muscle, making the cornea a more unlikely location for these structures when considering the options provided.