In muscle cells, myosin molecules continue moving along actin molecules as long as:
a. ATP is present and troponin is not bound to Ca²⁺.
b. ADP is present and tropomyosin is released from intracellular stores.
c. ADP is present and the intracellular acetylcholine level is high.
d. ATP is present and the intracellular Ca²⁺ concentration is high.

Which of the following is critical to the function of most exoskeletons, endoskeletons, and hydrostatic skeletons?

a. Muscles interact with the skeleton in antagonistic groups.

b. Muscles attach to each of these types of skeletons via tendons.

c. Muscles extend joints by pushing skeletal elements.

d. Segments of the body or limbs are extended when paired muscles relax in unison.

How did data on sarcomere structure inspire the sliding-filament model of muscle contraction?

Explain why the observation that muscle cells contain many mitochondria and extensive smooth endoplasmic reticulum turned out to be logical once the molecular mechanism of muscular contraction was understood.

Rigor mortis is the stiffening of a body after death that occurs when myosin binds to actin but cannot unbind. What prevents myosin from unbinding?

Which of the following statements regarding control of muscle tissue is/are correct? Select True or False for each statement.

T/F All skeletal muscles are voluntary.

T/F Cardiac muscle is involuntary.

T/F Some smooth muscle tissues are voluntary, and others are involuntary.

T/F Parasympathetic and sympathetic neurons innervate skeletal, cardiac, and smooth muscle tissues.