What type of junctions allow for fast signal transmission in animal cells?

Gap junctions are specialized intercellular connections that allow for the direct transfer of electrical and chemical signals between adjacent animal cells. They are formed by connexins, which create channels that span the membranes of two adjacent cells. This structure allows ions and small molecules to pass freely between the cells, facilitating rapid communication and coordination in tissues, especially in excitable tissues like cardiac and smooth muscle.

In contrast, desmosomes primarily provide mechanical strength and stability to tissues by anchoring cells together, but they do not play a role in signal transmission. Tight junctions function as barriers that regulate the passage of substances between the extracellular space and the cell, maintaining distinct cellular compartments but are not involved in signal transmission. Plasmodesmata are junctions found in plant cells that connect adjacent cells and allow for the transport of water, solutes, and signaling molecules, but they are not present in animal cells. Therefore, gap junctions are the correct choice for fast signal transmission in animal cells.