1: Each actin molecule in a skeletal muscle cell acts as an enzyme, binding to and splitting ATPmolecules, and releasing their energy.

True/False

2: An action potential in a skeletal muscle fiber lasts about 2/3 as long as the twitch it causes.

True/False

3: Metabolism of glucose is the fastest way for a skeletal muscle cell to increase its supply of ATP in order to meet the energy demands during a period of heavy exercise.

True/False

4: The tendons of skeletal muscles are slightly elastic because of the inherent ability of each collagen fiber within them to stretch under force and then recoil to its original length when the force is removed.

True/False

5: Whenever signals are generated in the spindle fibre of a skeletal muscle, they are passed to neurons in the spinal cord which stimulate the muscle to contract.

True/False

6: The thick filaments of smooth muscle are longer than those of skeletal muscle.

True/False

7: Smooth muscle sustains contractions longer and with less fatigue than skeletal muscle.

True/False

8: The strength of contraction in a single-unit smooth muscle depends on the number of its motor units that are activated.

True/False

For questions with multiple blanks please write all answers in the provided text box, separating them with commas.

9: Name a protein that is found in skeletal muscle cells, but not in smooth muscle cells:

10: A single motor neuron, together with all of the skeletal muscle cells to which it carries signals, are collectively called a

Choose the one best answer of those provided for each question:

11: The binding of a molecule of ATP to a myosin head group in a skeletal muscle fiber causes the head group's other binding site to decrease its affinity for

A. Ca++ ions.
B. ATP.
C. actin.
D. thick filaments.
E. tropomyosin.

12: ATP molecules provide energy in a skeletal muscle cell for all of but one the following purposes. Which is the exception?

A. The active transport of K+ ions into the cell and Na+ ions out of the cell.
B. The power stroke of contraction
C. The active transport of calcium ions out of the cell following an action potential
D. Allowing myosin head groups to detach from actin
E. The active transport of calcium ions into the sarcoplasmic reticulum

13: DHP (dihydropyridine) receptors in the membrane of the t-tubules of a skeletal muscle cell

A. respond to action potentials.
B. are physically connected to ions channels in the membrane of the sarcoplasmic reticulum.
C. are responsible for the release of Ca++ ions into the cell's interior.
D. form an essential element in excitation-contraction coupling.
E. All of the above are true.

14: Troponin in skeletal muscle cells

A. is a component of the thick filaments.
B. binds to Ca++ ions, allowing contraction to begin.
C. blocks the sites at which myosin binds to actin, while the cell is at rest.
D. forms crossbridges during contraction.
E. A and C.

15: Which of the following helps to return the sarcomeres of a skeletal muscle to their normal resting lengths following an isotonic contraction?

A. Titin molecules
B. Actin-myosin crossbridges
C. The load borne by the muscle
D. Troponin molecules
E. A and C

16: All but one of the statements below is correct. Which one is not? The tension developed in a contracting skeletal muscle cell

A. is directly proportional to the number of crossbridges.
B. always causes the muscle to shorten.
C. is higher during tetanic contraction than during a single twitch.
D. is determined by the length that the sarcomeres had just before contraction began.

17: Fatigue of skeletal muscle cells may be associated with

A. increase in the acidity of the cell's cytoplasm caused by lactic acid.
B. increase in the acidity, caused by lactic acid, of the interstitial fluid that bathes the cells.
C. increased levels of inorganic phosphate in the cell's cytoplasm.
D. a change in the concentration of extracellular K+ ions.
E. All of the above

18: In smooth muscle cells, caldesmon that is not bound to phosphate

A. activates myosin light-chain kinase, allowing contraction to begin.
B. catalyzes the removal of inorganic phosphate from myosin.
C. stimulates the Ca++/ATPase pumps that expel Ca++ ions from the cell.
D. binds to actin, preventing crossbridge formation.
E. shifts tropomyosin from its position covering actin's binding sites.