4 The Muscular System Free Online FlashCards

What are key features and roles of skeletal muscle?

Skeletal muscle is usually attached to bones by tendons. Its striated fibers are generally under voluntary control and help produce movement, maintain posture, and generate heat.

What is a sarcomere made of?

A sarcomere is the basic contractile unit within a myofibril. It contains thin actin filaments and thick myosin filaments.

How does calcium enable a skeletal muscle fiber to contract?

A nerve signal causes the sarcoplasmic reticulum to release calcium. Calcium exposes binding sites on actin, allowing myosin to pull the thin filaments inward; the filaments slide past one another rather than shortening.

What is a motor unit, and how can recruitment affect force?

A motor unit consists of a motor neuron and the muscle fibers it controls. Recruiting more motor units generally increases muscle force.

How do abduction and adduction differ?

Abduction moves a body part away from the body's midline; adduction moves it toward the midline.

How do agonists, antagonists, and synergists differ?

The agonist, or prime mover, produces most of a movement. The antagonist opposes or controls it, while synergists assist the agonist or help steady a joint.

What happens during a concentric contraction?

In a concentric contraction, an active muscle shortens, as when lifting a weight.

How do the quadriceps femoris and hamstrings act at the knee?

The quadriceps femoris extends the knee, while the hamstrings flex it. These opposing actions help coordinate knee movement.

Where is cardiac muscle found, and what does it do?

Cardiac muscle forms the heart wall. Its striated cells contract involuntarily to pump blood.

Where is smooth muscle found, and what does it do?

Smooth muscle is nonstriated and involuntary. It occurs in hollow organs and blood vessels, where it can move substances or regulate vessel diameter.

How do connective tissues relate to muscle fibers and tendons?

Connective-tissue layers surround individual muscle fibers, bundles of fibers, and the whole muscle. These layers continue into tendons that attach muscle to bone.

What are two roles of ATP in muscle contraction?

ATP supplies energy for the cross-bridge cycle and helps myosin detach from actin.