Skeletal Muscle Quiz
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During the process of excitation-contraction coupling in skeletal muscle, calcium is released from the sarcoplasmic reticulum by:
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Inositol triphosphate (IP3)
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Protein kinase A
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An increase in intracellular Ca2+ concentration
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Membrane depolarization
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An increase in intracellular Na+ concentration
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Do you know what the study of muscles is called? It's Myology. Today, you are going to play a skeletal muscle quiz. Skeletal muscle is one of the human body's three essential muscle tissues. Every skeletal muscle has thousands of muscle fibers that are wrapped together by connective tissue sheaths. What do you really know about skeletal muscle? Seems like See morewe are about to find out when you take this quiz. Good luck!
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- 2.
Which of the following causes rigor in skeletal muscle?
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No action potentials in motorneurons
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An increase in intracellular Ca2+ level
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A decrease in intracellular Ca2+ level
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An increase in ATP level
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A decrease in ATP level
Correct Answer
A. A decrease in ATP levelExplanation
When there is a decrease in ATP level in skeletal muscle, it leads to rigor. ATP is required for muscle relaxation as it provides energy for the detachment of myosin heads from actin filaments. When ATP levels decrease, the myosin heads remain attached to actin, causing the muscles to become stiff and rigid. This condition is known as rigor.Rate this question:
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- 3.
Which of the following is NOT a way of increasing the tension of a given muscle contraction?
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Increasing the frequency of action potentials down the motor neuron
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Increasing the number of motor units recruited
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Increasing the [K+] in the extracellular solution
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Increasing the diameter of individual muscle fibers
Correct Answer
A. Increasing the [K+] in the extracellular solutionExplanation
Increasing the [K+] in the extracellular solution is not a way of increasing the tension of a given muscle contraction. This is because an increase in extracellular potassium concentration would actually have the opposite effect and decrease muscle contraction. Potassium ions play a role in repolarizing the muscle cell membrane after an action potential, so an increase in extracellular potassium would interfere with this process and impair muscle function.Rate this question:
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- 4.
When skeletal muscle is in its resting state, myosin cross-bridges are directly prevented from binding to actin molecules by which protein?
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Calmodulin
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Troponin
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Tropomyosin
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Titin
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Phospholamban
Correct Answer
A. TropomyosinExplanation
Tropomyosin is the protein that directly prevents myosin cross-bridges from binding to actin molecules when skeletal muscle is in its resting state.Rate this question:
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- 5.
The amount of force produced by a skeletal muscle can be increased by which of the following changes?
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Increasing extracellular Mg2+
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Decreasing extracellular Ca2+
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Increasing the activity of acetylcholine esterase
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Decreasing the interval between contractions
Correct Answer
A. Decreasing the interval between contractionsExplanation
Decreasing the interval between contractions can increase the amount of force produced by a skeletal muscle. This is because a shorter interval allows for more frequent contractions, leading to a higher overall force output. When the interval between contractions is decreased, the muscle has less time to relax and recover, resulting in a sustained contraction and increased force generation. This is known as summation of contractions, where the force of each contraction adds up to produce a greater overall force.Rate this question:
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- 6.
In skeletal muscle, which of the following events occurs before depolarization of the T tubules in the mechanism of excitation-contraction coupling?
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Depolarization of the sarcolemmal membrane
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Opening of Ca2+ release channels on the sarcoplasmic reticulum (SR)
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Uptake of Ca2+ into the SR by Ca2+ ATPase
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Binding of Ca2+ to troponin C
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Binding of actin and myosin
Correct Answer
A. Depolarization of the sarcolemmal membraneExplanation
Before depolarization of the T tubules, the sarcolemmal membrane must first depolarize. This depolarization triggers the opening of Ca2+ release channels on the sarcoplasmic reticulum (SR), allowing Ca2+ to be released into the cytoplasm. This Ca2+ release then leads to the binding of Ca2+ to troponin C, which allows for the binding of actin and myosin and initiates the process of muscle contraction. Therefore, depolarization of the sarcolemmal membrane is the initial event in the mechanism of excitation-contraction coupling in skeletal muscle.Rate this question:
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- 7.
Repeated stimulation of skeletal muscle fiber causes a sustained contraction (tetanus). Accumulation of which solute in intracellular fluid is responsible for tetanus?
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Na+
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K+
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Cl-
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Mg2+
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Ca2+
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Troponin
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Calmodulin
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Adenosine triphosphate (ATP)
Correct Answer
A. Ca2+Explanation
Repeated stimulation of skeletal muscle fiber causes a sustained contraction called tetanus. This is due to the accumulation of calcium ions (Ca2+) in the intracellular fluid. Calcium ions play a crucial role in muscle contraction by binding to troponin, which allows the interaction between actin and myosin filaments. The binding of calcium ions to troponin triggers a series of events that lead to muscle contraction. Therefore, the accumulation of calcium ions in the intracellular fluid is responsible for tetanus.Rate this question:
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- 8.
Why is the latent period longer during an isotonic twitch of a skeletal muscle fiber than it is during an isometric twitch?
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Excitation-contraction coupling is slower during an isotonic twitch.
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Action potentials propagate more slowly when the fiber is shortening, so extra time is required to activate the entire fiber.
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In addition to the time for EC coupling, it takes extra time for enough cross-bridges to attach to make the tension in the muscle fiber greater than the load
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Fatigue sets in much more quickly during isotonic contractions, and when muscles are fatigued, the cross-bridges move much more slowly
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The latent period is longer because isotonic twitches only occur in slow (type I) muscle fibers.
Correct Answer
A. In addition to the time for EC coupling, it takes extra time for enough cross-bridges to attach to make the tension in the muscle fiber greater than the loadExplanation
During an isotonic twitch, the muscle fiber is shortening, which means that action potentials propagate more slowly. This slower propagation requires extra time to activate the entire fiber. Additionally, it takes time for enough cross-bridges to attach and generate tension greater than the load. This delay in cross-bridge attachment contributes to the longer latent period during an isotonic twitch compared to an isometric twitch.Rate this question:
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- 9.
Which correctly characterizes a “fast-oxidative” type of skeletal muscle fiber?
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Few mitochondria and high glycogen content
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Low myosin ATPase rate and few surrounding capillaries
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Low glycolytic enzyme activity and intermediate contraction velocity
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High myoglobin content and intermediate glycolytic enzyme activity
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Small fiber diameter and fast onset of fatigue
Correct Answer
A. High myoglobin content and intermediate glycolytic enzyme activityExplanation
A "fast-oxidative" type of skeletal muscle fiber is characterized by high myoglobin content and intermediate glycolytic enzyme activity. Myoglobin is a protein that stores oxygen in muscle cells, allowing for efficient oxygen delivery during exercise. Intermediate glycolytic enzyme activity suggests that these fibers can utilize both aerobic and anaerobic energy pathways. This combination of high myoglobin content and intermediate glycolytic enzyme activity allows for sustained, moderate-intensity exercise.Rate this question:
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- 10.
The amount of force produced by a skeletal muscle can be increased by which of the following?
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Decreasing the activity of nicotinic ACh receptor
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Decreasing extracellular Ca2+
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Increasing the activity of acetylcholinesterase
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Decreasing the interval between contractions
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Greatly increasing the starting muscle length.
Correct Answer
A. Decreasing the interval between contractionsExplanation
Decreasing the interval between contractions can increase the amount of force produced by a skeletal muscle. This is because decreasing the interval between contractions allows for more frequent muscle contractions, leading to a higher overall force output. By reducing the time between contractions, the muscle has less time to relax and can generate more force over a shorter period of time. This increased frequency of contractions can result in a stronger muscle contraction and greater force production.Rate this question:
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- 11.
Repetitive stimulation of a skeletal muscle fiber will cause an increase in contractile strength because repetitive stimulation causes an increase in what?
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The duration of cross-bridge cycling
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The concentration of calcium in the myoplasm
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The magnitude of the end-plate potential
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The number of muscle myofibrils generating tension
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The velocity of muscle contraction
Correct Answer
A. The duration of cross-bridge cyclingExplanation
Repetitive stimulation of a skeletal muscle fiber causes an increase in contractile strength because it leads to an increase in the duration of cross-bridge cycling. Cross-bridge cycling refers to the process by which myosin heads bind to actin filaments and generate force during muscle contraction. When a muscle fiber is stimulated repeatedly, the cross-bridge cycling continues for a longer duration, allowing for more force generation and ultimately increasing the contractile strength of the muscle.Rate this question:
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- 12.
During normal voluntary movement, which is true regarding muscle fiber recruitment?
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Large muscle fibers are recruited before small muscle fibers.
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Fast glycolytic muscle fibers are recruited before slow oxidative muscle fibers.
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Weak muscle fibers are recruited before strong muscle fibers.
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Poorly perfused muscle fibers are recruited before richly perfused muscle fibers.
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Anaerobic fibers are recruited before aerobic fibers.
Correct Answer
A. Weak muscle fibers are recruited before strong muscle fibers.Explanation
During normal voluntary movement, weak muscle fibers are recruited before strong muscle fibers. This is because the body follows the principle of "size principle" in muscle fiber recruitment. According to this principle, motor units consisting of smaller, weaker muscle fibers are recruited first, followed by larger, stronger muscle fibers as the intensity of the movement increases. This allows for finer control and precision in movements, as well as conserving energy by only recruiting the necessary muscle fibers for the task at hand.Rate this question:
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- 13.
Which of the following temporal sequences is correct for excitation-contraction coupling in skeletal muscle?
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Increased intracellular [Ca2+]; action potential in the muscle membrane; cross-bridge formation
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Action potential in the muscle membrane; depolarization of the T tubules; release of Ca2+ from the sarcoplasmic reticulum (SR)
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Action potential in the muscle membrane; splitting of adenosine triphosphate (ATP); binding of Ca2+ to troponin C
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Release of Ca2+ from the SR; depolarization of the T tubules; binding of Ca2+ to troponin C
Correct Answer
A. Action potential in the muscle membrane; depolarization of the T tubules; release of Ca2+ from the sarcoplasmic reticulum (SR)Explanation
Excitation-contraction coupling in skeletal muscle begins with an action potential in the muscle membrane, which then leads to depolarization of the T tubules. This depolarization triggers the release of Ca2+ from the sarcoplasmic reticulum (SR). Therefore, the correct temporal sequence is: Action potential in the muscle membrane; depolarization of the T tubules; release of Ca2+ from the SR.Rate this question:
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- 14.
In skeletal muscle, which of the following events occurs before depolarization of the T tubules in the mechanism of excitation-contraction coupling?
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Depolarization of the sarcolemmal membrane
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Opening of Ca2+ release channels on the sarcoplasmic reticulum
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Uptake of Ca2+ into the SR by Ca2+ ATPase
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Binding of Ca2+ to troponin C
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Binding of actin and myosin
Correct Answer
A. Depolarization of the sarcolemmal membraneExplanation
Before the depolarization of the T tubules in the mechanism of excitation-contraction coupling in skeletal muscle, the sarcolemmal membrane must depolarize. This depolarization triggers the opening of Ca2+ release channels on the sarcoplasmic reticulum, allowing the release of Ca2+ into the cytoplasm. This Ca2+ then binds to troponin C, which causes a conformational change in the troponin-tropomyosin complex, allowing actin and myosin to bind and initiate muscle contraction. The depolarization of the sarcolemmal membrane is the initial event that sets off the cascade of events leading to muscle contraction.Rate this question:
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- 15.
In a controlled experiment, radiolabeled ATP is injected into isolated muscle fiber. The muscle is stimulated and allowed to contract for 10 seconds. An autoradiogram from a biopsy of the muscle taken during this contraction will show radiolabeled ATP bound to what structure?
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Actin
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Myosin
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Sarcopasmic reticulum
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Tropomyosin
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Troponin C
Correct Answer
A. MyosinExplanation
During muscle contraction, myosin and actin interact to generate force and movement. Myosin is a motor protein that binds to actin and uses ATP as an energy source to perform its function. In this experiment, radiolabeled ATP is injected into the muscle fiber, and during contraction, the radiolabeled ATP will bind to myosin as it carries out its role in muscle contraction. Therefore, an autoradiogram from a biopsy taken during this contraction will show radiolabeled ATP bound to myosin.Rate this question:
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Current Version
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Aug 28, 2023Quiz Edited by
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Oct 27, 2011Quiz Created by
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