9. Muscle Tissue

Aerobic exercise results in all of the following except:

a. More capillaries surrounding muscle fibers

b. More mitochondria in muscle cells

c. Increased size and strength of existing muscle cells

d. More myoglobin

What is the importance of acetylcholinesterase in muscle cell contraction?

Explain what is meant by the term excitation-contraction coupling.

Define and draw a motor unit.

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.

Explain how a slight (but smooth) contraction differs from a vigorous contraction of the same muscle. Use the concepts of multiple motor unit summation.

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⁺.

What is the basic mechanism of contraction at the level of myofilaments?

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.

Which of the following statements accurately describes the role of ATP in a muscle contraction?

a. ATP is directly responsible for the power stroke.

b. ATP moves troponin and tropomyosin away from actin.

c. ATP breaks the actin/myosin attachment and 'cocks' the myosin head.

d. ATP causes the myofilaments to shorten.

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.

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

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.

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

A muscle fiber changes length during isotonic concentric and isotonic eccentric contractions.

Tell where each of the three types of muscle tissue would be found in the body. What is meant by the statement, 'Smooth muscles are involuntary in action'?