NCLEX : Muscle Physiology

Study concepts, example questions & explanations for NCLEX

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Example Questions

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Example Question #1 : Muscle Physiology

The individual unit of muscle contraction in a muscle fibril is referred to as the __________.

Possible Answers:

sarcomere

sarcolemma

sliding filament

sarcoplasmic reticulum

Correct answer:

sarcomere

Explanation:

The individual contractile unit of a muscle fibril is referred to as the sarcomere. These units are made of actin and myosin filaments and joined by Z-lines. The sliding filament theory refers to the idea that muscle contraction is the result of myosin strands within the fibril pulling themselves along actin strands similar to pulling on a rope, which shortens the whole sarcomere. The sarcolemma is the specialized cell membrane around the muscle fibril, and the sarcoplasmic reticulum is the smooth endoplasmic reticulum found within the muscle cell.

Example Question #2 : Muscle Physiology

Which of the following is the correct order of structures in a skeletal muscle, from largest to smallest?

Possible Answers:

Fibril - fascicle - fiber

Fiber - fascicle - fibril

Fascicle - fiber - fibril

Fascicle - fibril - fiber

Fiber - fibril - fascicle

Correct answer:

Fascicle - fiber - fibril

Explanation:

The largest unit of muscle tissue is the fascicle. Each fascicle is made up of a bundle of muscle fibers, and every muscle fiber is made up of many fibrils (called myofibrils).  

Example Question #3 : Muscle Physiology

The muscle body is encased in which of the following?

Possible Answers:

The endomysium

The perimysium

None of these

The epimysium

Correct answer:

The epimysium

Explanation:

The muscle body is encased in a fibrous elastic sheath called the epimysium (epi meaning on or above and mys meaning muscle). It is composed of dense irregular connective tissue and is continuous with tendon fibers. The perimysium surrounds muscle fascicles, while the endomysium surrounds muscle fibers.

Example Question #4 : Muscle Physiology

Which of the following correctly describes an isometric muscle contraction?

Possible Answers:

This form of contraction can either be eccentric or concentric

The amount of muscle tension increases without any change in the length of the muscle or the angle of the joint

There is a rapid burst of mechanical energy for a short powerful movement

The length of the muscle shortens and the angle of the joint changes during the contraction

Correct answer:

The amount of muscle tension increases without any change in the length of the muscle or the angle of the joint

Explanation:

Isometric muscle contraction are those in which the tension in the muscle increases, but the muscle does not change length, nor does the angle of the joint change. An example would be attempting to push or lift an object that is too heavy to move. This is in contrast to isotonic contraction, in which muscle tension remains constant, but the muscle length and joint angle both change.

Example Question #5 : Muscle Physiology

During contraction, the A band of the sarcomere does which of the following?

Possible Answers:

It does not change

It thickens

It shortens

It lengthens

Correct answer:

It does not change

Explanation:

The A band in the sarcomere is created by the bipolar myosin filaments, joined at the M band. During contraction, the heads of the myosin filaments bind with the actin filament and pull it toward the M band at the center of the sarcomere. The myosin filaments do not themselves change length, and because of that the width of the A band does not change during contraction.

Example Question #6 : Muscle Physiology

In the sliding filament theory of muscle contraction, all but which of the following are functions of ATP?

Possible Answers:

It moves the myosin head into a high energy "cocked" position

It allows the myosin head to detach from the actin filament

It moves tropomyosin off of actin binding sites

ATP does all of these things during muscle contraction

Correct answer:

It moves tropomyosin off of actin binding sites

Explanation:

According to the sliding filament theory of muscle contraction, ATP binds to the myosin head and is hydrolyzed to ADP and inorganic phosphate. The energy released during this change draws the myosin head back into a high energy state, from which it is able to bind with actin and execute its "power stroke," leading to muscle contraction. ADP and inorganic phosphate then are released from the myosin head and replaced by a new molecule of ATP, which allows the myosin head to detach from the actin binding site.  

Example Question #7 : Muscle Physiology

All of the following features are unique to cardiac muscle cells except:

Possible Answers:

They form branching chains

They are non-striated

There are gap junctions between cells

They are linked together via intercalated discs

Correct answer:

They are non-striated

Explanation:

Cardiac muscle cells are striated, branching cells that are linked by structures called intercalated discs. These discs are composed of gap junctions, which allow the free passage of electrical signaling between heart cells, and very strong attachment points called desmosomes.

Example Question #8 : Muscle Physiology

A nurse is examining a patient who has muscle pain and fatigue after working out. He determines that the patient has muscle strain. This is generally caused by which of the following?

Possible Answers:

There is damage to ligamentous attachments

Hypertrophy is causing swelling of the muscle fiber

Excessive contraction causes tetany in the muscle body

The actin and myosin filaments have been pulled past their ability to overlap

Correct answer:

The actin and myosin filaments have been pulled past their ability to overlap

Explanation:

Muscle strain is often caused by over stretching, during which actin and myosin heads are pulled to the extent that they are no longer overlapping, possibly to the point of causing tears in muscle tissue. Tears in ligaments are sprains, rather than strains.

Example Question #9 : Muscle Physiology

Which is the only muscle type that is non-striated?

Possible Answers:

Voluntary

Skeletal muscle

Smooth muscle

Cardiac muscle

Correct answer:

Smooth muscle

Explanation:

The only type of muscle that is not striated is smooth muscle. Smooth muscle does not use sarcomeres for contraction - rather, each muscle cell is a spindle that is covered in a mesh of contractile fibrils. These fibrils contract in unison when calcium enters the cell.

Example Question #10 : Muscle Physiology

Which of the following is the smallest unit of contractile tissue in cardiac and skeletal muscle cells?

Possible Answers:

Actin filaments

The myofibril

The sarcomere

Myosin filament

Correct answer:

The sarcomere

Explanation:

The smallest contractile unit in muscle tissue is the sarcomere. Myofibrils are made up of many sarcomeres attached end-to-end at a series of dark lines (hence the term "striated") called Z lines. Each sarcomere contains actin and myosin filaments, which pull together during contraction to shorten the sarcomere.

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