9. Muscle Tissue

Which of the following energy sources would provide the majority of the ATP for a person running a 26-mile marathon?

a. Stored ATP

b. Glycolytic catabolism

c. Oxidative catabolism

d. Creatine phosphate

Chemical A binds and blocks acetylcholine receptors of muscle cells. Chemical B floods the cytoplasm of muscle cells with calcium ions. Which chemical would make the best muscle relaxant, and why?

Muscle-relaxing drugs are administered to a patient during major surgery. Which of the two chemicals described next would be a good skeletal muscle relaxant and why?

• Chemical A binds to and blocks ACh receptors of muscle cells.

• Chemical B floods the muscle cells' cytoplasm with Ca²⁺.

Characteristics of isometric contractions include all but:

a. Shortening

b. Increased muscle tension throughout the contraction phase

c. Absence of shortening

d. Used in resistance training

Order the following events of excitation and excitation-contraction coupling. Put 1 by the first event, 2 by the second, and so on.

____ The motor end plate generates an end-plate potential.

____ The action potential spreads along the T-tubules, SR Ca²⁺ channels are pulled open, and Ca²⁺ floods the cytosol.

____ Acetylcholine binds to receptors on the motor end plate, and ligand-gated ion channels open.

____ Ca²⁺ bind troponin, which allows tropomyosin to move away from the actin active site, initiating a contraction cycle.

____ The action potential propagates through the sarcolemma and dives deeply into the cell along the T-tubules.

A muscle fiber relaxes when:

a. The concentration of Ca²⁺ in the cytosol returns to resting levels.

b. The supply of ATP is exhausted.

c. Ca²⁺ flood the cytosol.

d. Acetylcholine is released from the axon terminal and the sarcolemma depolarizes.

a. Describe the structure of a sarcomere and indicate the relationship of the sarcomere to myofilaments.

b. Explain the sliding filament model of contraction using appropriately labeled diagrams of a relaxed and a contracted sarcomere.

What is the role of the calcium ion in the signaling of an action potential at the neuromuscular junction?

When Eric returned from jogging, he was breathing heavily and sweating profusely, and he complained that his legs ached and felt weak. On the basis of what you have learned about muscle energy metabolism, respond to the following questions: c. What metabolic product(s) might account for his sore muscles and his feeling of muscle weakness?

What structural feature of a skeletal muscle fiber propagates action potentials into the interior of the cell?

Describe the events that occur from the time calcium ions enter the axon terminal at the neuromuscular junction until muscle cell contraction occurs.

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Stimulation by a motor neuron before a muscle fiber has fully relaxed results in a condition called wave summation.

What would happen if a muscle completely ran out of ATP during a muscle contraction.