Final answer:
Cross-bridges are myosin heads in muscle cells that attach to actin filaments to generate force and movement. Motor end plates are locations on muscle fibers where acetylcholine receptors are found.
Step-by-step explanation:
The term 'cross-bridges' refers to the myosin heads in muscle cells. Cross-bridge formation is a key step in muscle contraction, where the myosin heads attach to the actin filaments to generate force and produce movement. The myosin heads undergo a series of conformational changes, powered by ATP hydrolysis, to pull the actin filaments closer together.
Another term mentioned in the question, 'motor end plates', are actually locations on the muscle fibers where acetylcholine receptors are located. The release of acetylcholine from the axon terminal triggers the generation of an action potential and leads to muscle contraction.