NCLEX : Muscle Physiology

Study concepts, example questions & explanations for NCLEX

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Example Questions

Example Question #11 : Muscle Physiology

The sliding filament theory of muscle contraction involves the __________ attaching to __________ and then pulling during the power stroke. 

Possible Answers:

actin head . . . myosin

myosin head . . . actin

troponin . . . actin

myosin . . . tropomyosin

Correct answer:

myosin head . . . actin

Explanation:

The sliding filament theory of muscle contraction involves the myosin head attaching to actin and then pulling during the power stroke. Troponin is a protein attached to tropomyosin, a thin strand wrapping around the actin filament. When calcium enters the cell, troponin moves toward it, pulling the tropomyosin strand away from actin binding sites and allowing the myosin head to bind. 

Example Question #61 : Musculoskeletal System And Anatomy

Which of the following molecules binds to troponin during muscle contraction, triggering tropomyosin to move away from the actin binding sites and allowing the myosin head to form a cross bridge?

Possible Answers:

Sodium

Calcium

ATP

ADP

Correct answer:

Calcium

Explanation:

During a muscle cell action potential, calcium enters the cell via t-tubules, which are specialized invaginations of the sarcoplasmic reticulum. Calcium binds with troponin, which pulls the tropomyosin strand away from actin binding sites and allows myosin heads to bind. Neither sodium nor potassium bind to troponin, and ATP and ADP both bind to myosin, rather than troponin.

Example Question #62 : Musculoskeletal System And Anatomy

Which of the following is the name of the modified endoplasmic reticulum found in muscle cells?

Possible Answers:

The sarcomere

The myoplasmic reticulum

The sarcoplasmic reticulum

The t-tubule

Correct answer:

The sarcoplasmic reticulum

Explanation:

Muscle cells have a specialized endoplasmic reticulum called the sarcoplasmic reticulum. The sarcoplasmic reticulum regulates the calcium ion concentration in the cytoplasm of striated muscle cells, and so plays a significant role in muscle contraction and relaxation. The T-tubule is a specialized invagination of the sarcoplasmic reticulum, and the sarcomere is the single contractile unit of a muscle fibril. There is no muscle structure called the mycoplasmic reticulum.

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