Fill in the blanks to describe muscles and how they operate.
Smooth muscle is usually not under voluntary control, although it may be influenced consciously. It lacks the characteristic striation of skeletal muscle. Moreover, smooth muscle can be made to contract by simple periodic spontaneous contraction (autorhythmicity) of its fibres.
Muscles extend from one bone to another and cross at least one joint. Muscle is connected to the bone by a tendon. The most stationary end of the muscle is the origin, and the end attached to the bone undergoing the greatest movement is the insertion.
Members of a group of muscles working together to produce a movement are called synergists. Muscles are typically grouped so that the action of one muscle (or group of muscles) is opposed by that of another muscle (or group of muscles). For example in the movement of the elbow, the biceps brachii flexes the elbow and is the agonist, while the triceps brachii extends the elbow and is the antagonist.