4 The Muscular System Free Online FlashCards

What are the key features of skeletal muscle?

Skeletal muscle has long, cylindrical, striated fibers with many nuclei. It is usually attached to bones and mostly under voluntary control.

Where is smooth muscle found, and how is it controlled?

Smooth muscle has spindle-shaped cells with one nucleus and no visible striations. It acts involuntarily in hollow organs and blood vessel walls.

What distinguishes cardiac muscle?

Cardiac muscle consists of branched, striated cells, usually with one nucleus. It is found in the heart wall and contracts involuntarily to pump blood.

How is skeletal muscle organized from largest to smallest?

Whole muscle → fascicles → muscle fibers → myofibrils → sarcomeres → myofilaments.

How does a sarcomere shorten during contraction?

A sarcomere shortens as thin actin filaments slide past thick myosin filaments. The filaments themselves do not significantly shorten.

What initiates skeletal muscle excitation–contraction coupling?

A motor neuron releases acetylcholine, triggering an electrical impulse along the sarcolemma and down T-tubules. This leads the sarcoplasmic reticulum to release calcium.

How does calcium expose myosin-binding sites on actin?

Calcium binds to troponin, shifting tropomyosin and exposing myosin-binding sites on actin.

What are two roles of ATP in skeletal muscle?

ATP enables myosin to detach from actin and prepares the myosin head for another cycle. It is also required to pump calcium back into the sarcoplasmic reticulum.

What happens in a skeletal muscle fiber when stimulation ends?

Calcium is pumped back into the sarcoplasmic reticulum, and tropomyosin again blocks actin’s binding sites.

How is smooth muscle contraction regulated?

Calcium binds to calmodulin, which activates enzymes that enable myosin to interact with actin. Smooth muscle does not use troponin to regulate contraction.

How does calcium support cardiac muscle contraction?

Calcium entering a heart muscle cell helps trigger additional calcium release from the sarcoplasmic reticulum, supporting contraction.

How do an agonist and antagonist differ?

The agonist, or prime mover, produces the movement; the antagonist produces or controls the opposing movement. In elbow flexion, the biceps brachii is a major agonist and the triceps brachii is an antagonist.