Question 1

Which of the following best describes the role of calcium ions ($$\mathrm{Ca$$^{2+}$$}) in $$skeletal muscle contraction?

Accepted Answer

Calcium ions bind to troponin, causing tropomyosin to shift and expose myosin-binding sites on actin.

Question 2

A muscle twitch consists of three phases: latent period, contraction, and relaxation. If the latent period lasts 2 ms, the contraction phase lasts 10 ms, and the relaxation phase lasts 12 ms, what is the total duration of the muscle twitch?

Accepted Answer

$$24\ \mathrm{ms}$$

Question 3

Which statement best explains the phenomenon of wave (temporal) summation in skeletal muscle?

Accepted Answer

A second stimulus arrives before the muscle has fully relaxed, causing increased tension.

Question 4

During a laboratory experiment, a student increases the frequency of electrical stimulation to a frog muscle. Which outcome is most likely as the frequency approaches the threshold for fused tetanus?

Accepted Answer

The muscle tension will plateau at a maximum value as relaxation disappears between stimuli.

Question 5

Which equation correctly represents the calculation of total muscle twitch duration ($$T_{total}) $$given the latent period ($$T_{latent}$$), contraction phase ($$T_{contraction}$$), and relaxation phase ($$T_{relaxation}$$)?

Accepted Answer

$$T_{total} = T_{latent} + T_{contraction} + T_{relaxation}$$

Question 6

A patient is unable to generate sufficient muscle force to lift a heavy object. Which physiological process is most likely impaired?

Accepted Answer

Motor unit recruitment

Question 7

Which of the following best describes a motor unit?

Accepted Answer

A single motor neuron and all the muscle fibers it innervates.

Question 8

If the strength of a stimulus applied to a muscle is increased, which of the following is the most likely result?

Accepted Answer

More motor units will be recruited, increasing muscle tension.

Question 9

Which of the following is the correct sequence of events during excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential → calcium release → troponin binds calcium → tropomyosin shifts → cross-bridge formation

Question 10

A muscle fiber is stimulated at a frequency that allows partial relaxation between contractions. What is this phenomenon called?

Accepted Answer

Unfused tetanus

Question 11

Which of the following best explains why increasing the frequency of stimulation leads to greater muscle tension?

Accepted Answer

Calcium remains in the cytoplasm, allowing more cross-bridges to form before relaxation.

Question 12

During an EMG (electromyogram) recording, what does an increase in voltage amplitude most likely indicate?

Accepted Answer

An increase in the number of active motor units.

Question 13

Which of the following is the best definition of muscle tetanus in the context of laboratory experiments?

Accepted Answer

A sustained contraction resulting from high-frequency stimulation with no relaxation between stimuli.

Question 14

If a muscle is stimulated with a voltage below threshold, what will be the observed response?

Accepted Answer

No contraction will occur.

Question 15

Which formula would you use to calculate the average tension ($$T_{avg}) $$produced during a series of muscle twitches if the tensions recorded are $$T_1$$, $$T_2$$, ..., $$T_n$$?

Accepted Answer

$$T_{avg} = \dfrac{T_1$ + T_2$ + \ldots + T_n}{n}$$

Question 16

A student observes that increasing the stimulus voltage to a muscle increases the amplitude of the EMG signal. What is the most likely explanation?

Accepted Answer

More muscle fibers are being activated due to increased motor unit recruitment.

Question 17

Which of the following best describes the relationship between motor unit recruitment and muscle tension?

Accepted Answer

As more motor units are recruited, muscle tension increases.

Question 18

In a real-world scenario, why is motor unit recruitment important when lifting a heavy object?

Accepted Answer

It enables the muscle to generate enough force by activating additional motor units.

Question 19

Which of the following is true regarding the sarcomere during muscle contraction?

Accepted Answer

The Z lines move closer together as the thin filaments slide past the thick filaments.

Question 20

A muscle fiber is stimulated repeatedly at a frequency that does not allow any relaxation between contractions. What is the expected outcome?

Accepted Answer

The muscle will reach fused tetanus, producing maximal sustained tension.

Muscle Physiology: Muscle Twitch, Summation, Tetanus, and Motor Unit Recruitment

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