Chapter 6: excitable (they respond to stimuli, contractile (they can shorten, extensible (they can stretch, elastic (they can return to their original length after being shortened or stretched) Three types of muscles: skeletal: voluntary locomotion, posture, support internal organs, move blood and lymph, generate heat, cardiac: heart pumps blood, smooth: involuntary peristalsis, blood pressure, bronchial diameter, pupil size. Our bodies have over 600 skeletal muscles. Origin: stationary (or least moving) attachment site. Antagonistic muscles: pairs of muscle that oppose the movement of each other. Insertion: moving (primary action end) attachment site. contracts the other must be relaxed and stretching. Synergistic muscles: multiple muscles contributing to the movement. Tendinitis: inflammation of a tendon caused by overuse, misuse, or age, healing is slow because tendons have a poor blood supply, most effective treatment is rest. Muscle cramp: an involuntarily and forcibly contracted muscle that does not relax, contributors include electrolyte imbalance, dehydration, inadequate blood flow, excessive heat or cold.