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Across 1. muscle responsible for a body movement also called a prime mover 3. A brief contraction of a muscle fiber followed by relaxation 4. Increased force of contraction by a skeletal muscle fiber when a twitch occurs before the previous twitch relaxes 5. oxygen carrying pigment in RBC'S 7. contractile fibers in muscle cells 8. the structural and functional units of a myofibril 10. Rhythmic waves of muscular contraction in the walls of certain tubular organs 11. the end of a muscle attached to a movable part 12. the end of a muscle that attaches to a relatively immovable part 13. A motor neuron and its associated muscle fibers 14. layers of fibrous connective tissue

Down 2. chemicals that axons secrete on effectors or other neurons 3. Part of an acting filament 6. Protein that with actin forms the filaments that contract muscle fibers 9. muscles that assist the action of a prime mover