What term refers to long cylindrical multi-nucleated cells bundled together to form muscle tissue?

The term that refers to long cylindrical multi-nucleated cells bundled together to form muscle tissue is "muscle fibers." Muscle fibers are the basic cellular units of skeletal muscle, characterized by their elongated shape and multiple nuclei which result from the fusion of precursor myoblasts during development. This unique structure allows muscle fibers to efficiently contract and generate force.

Muscle fibers can be organized in various arrangements, contributing to different muscle functions and types. For instance, in skeletal muscle, these fibers are organized into fascicles, which are then bundled together to form whole muscles. This hierarchical organization is crucial for facilitating coordinated movement and strength.

In contrast, cardiac muscle pertains specifically to the muscle tissue found in the heart, which has a different structure and function. The terms "origin" and "antagonists" refer to concepts related to muscle attachments and muscle action, respectively, rather than describing the structure of the muscle cells themselves. Thus, muscle fibers is the term that directly describes the cylindrical, multi-nucleated cells that form muscle tissue.