Final answer:
Agonists are muscles primarily responsible for a movement, antagonists oppose their action, and synergists assist the agonists. Muscle fascicles are arranged in various patterns, which influence the muscle's force generation and motion range. Muscles are named based on their size, shape, location, and fiber direction.
Step-by-step explanation:
The principal muscles involved in movement are known as agonists, or prime movers, while the muscles that oppose their action are called antagonists. For example, the biceps brachii in the arm is the agonist when lifting a cup, as it is the prime mover of the action. The triceps brachii would act as the antagonist during this motion as it opposes the action of the biceps brachii. Synergists are muscles that assist the agonists in movement, such as the brachialis muscle which aids the biceps brachii. Synergists can also act as fixators that stabilize the origin of the prime mover, ensuring efficient movement.
The force generation of a muscle is influenced by the arrangement of its muscle fibers, known as fascicles. There are various fascicle arrangements, including parallel, circular, convergent, pennate, fusiform, and triangular. Each arrangement allows for a specific range of motion and capability to exert force, affecting the muscle's function. For instance, circular muscles function as sphincters to close openings in the body.
Skeletal muscles are named based on several characteristics, such as their size, shape, location, and the direction of their fibers. The tibialis anterior is named for its position and the bone it's associated with, while the names biceps brachii and pectoralis major refer to the muscle's origins, insertions, and the distinctive shape of the muscle.