Some athletes will consume only protein for several days before a competition, which reduces the amount of glycogen in both the muscle fibers and the liver. What effect would this have on their ability to perform activities that require short, powerful bursts of activity? How would it affect their ability to perform endurance activities?

Ms. Sanchez was in a motorcycle accident in which she lost the use of her right upper limb muscles due to significant nerve damage. However, when an electrode is inserted into her muscles, they are able to contract. Explain specifically why nerve damage caused her to lose the use of her muscles. Why can they still respond to stimulation from an electrode?

Mr. Nasheed has cerebral palsy and suffers severe skeletal muscle spasms as a result of his condition. He is prescribed the drug dantrolene, which prevents the release of Ca²⁺ from the SR. Explain how this will treat his muscle spasms.

Would you expect to find larger motor units in the postural muscles of the back or the muscles of the hand? Explain your answer.

A hypothetical poison blocks K⁺ leak channels. How would this affect the resting membrane potential of skeletal muscle fibers? Explain your reasoning.

The drug neostigmine blocks the activity of the enzyme acetylcholinesterase in the synaptic cleft. Predict the effects of this drug.

Explain why cardiac muscle cells and some smooth muscle cells will continue to contract even when their nerve supply has been removed

The poison curare (kyoo-RAH-ray) blocks the binding of acetylcholine to its receptors at the neuromuscular junction. What effects would you predict from such a poison? Can you think of any useful applications for it? Why might an overdose of it be lethal?

Jesse is a 2-year-old boy who presents with difficulty in walking and poor control of movements. When the doctor examines Jesse, she notices that when his muscles contract, they are very slow to relax and remain contracted well after the movement has been performed. She sends a sample of his tissue for genetic analysis, and the lab reports a genetic defect that causes the pumps in the SR to operate much more slowly than normal. How does a defect in DNA lead to a malfunctioning protein? How does this finding explain Jesse's symptoms?

Paola is a 3-year-old girl with a disease that reduces the ability of her mitochondria to generate ATP. Explain the specific effects of this disease on the ability of Paola's muscles to function properly. What other tissues and organs are likely to be especially affected by her disease, and why?

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

A property of all muscle cells is elasticity, which means that the tissue is able to stretch.

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The common function of all types of muscle tissue is to generate tension.

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The plasma membrane of a muscle cell is called the sarcoplasmic reticulum.

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Muscle cells are contractile, conductive, distensible cells.

How does a skeletal muscle fiber differ structurally from typical cells?

Match the following terms with the correct definition.      

____Z-disc     

____Sarcomere     

____A band     

____H zone     

____I band     

____M line

a. The dark band containing the entire length of the thick filament

b. The band of proteins in the middle of the H zone

c. The boundary between sarcomeres

d. The functional unit of contraction

e. The middle region of the A band containing only thick filaments

f. The light band containing only thin filaments

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

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

The resting membrane potential refers to the voltage difference across the membranes of excitable cells at rest.

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The concentration of Na⁺ is highest in the cytosol, and the concentration of K⁺ is highest in the extracellular fluid.

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The Na⁺/K⁺ pumps and gated channels maintain the Na⁺ and K⁺ gradients necessary for action potentials to occur.

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A depolarization is a change in membrane potential that makes the potential less negative.

Describe the three components of the neuromuscular junction.

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.

Muscle fibers generate more tension if the starting length of their sarcomeres is very short.

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

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Muscles that require a great deal of precise control will have large motor units.

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