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 a conformational change that moves tropomyosin away from actin's binding sites.

Question 2

A muscle is stimulated with increasing voltage. The minimum voltage required to elicit a visible contraction is called:

Accepted Answer

Threshold stimulus

Question 3

During a muscle twitch, which phase occurs immediately after the stimulus but before contraction begins?

Accepted Answer

Latent period

Question 4

Which of the following best explains why a single muscle cell cannot increase its response to a stronger single stimulus?

Accepted Answer

The muscle cell releases all available calcium ions in response to a single stimulus, making it an all-or-nothing event.

Question 5

If a muscle is stimulated repeatedly at a frequency where individual twitches fuse into a smooth, sustained contraction with no relaxation, this is called:

Accepted Answer

Complete tetanus

Question 6

A muscle maintains a constant length while tension increases. This type of contraction is known as:

Accepted Answer

Isometric contraction

Question 7

Which process allows a whole muscle to produce a graded response by activating more motor units as stimulus strength increases?

Accepted Answer

Recruitment (motor unit summation)

Question 8

Primary fatigue in skeletal muscle is most directly caused by:

Accepted Answer

Rapid buildup of lactic acid and toxic metabolites in the cytoplasm

Question 9

A muscle is subjected to repeated stimuli at a frequency just below tetanizing frequency. What is the expected outcome?

Accepted Answer

Incomplete tetanus with brief periods of relaxation

Question 10

Which of the following best describes the sequence of events in excitation-contraction coupling in skeletal muscle?

Accepted Answer

Action potential → calcium release from SR → calcium binds to troponin → tropomyosin moves → myosin binds actin

Question 11

A muscle is stimulated with a voltage higher than the maximal stimulus, but the force of contraction does not increase. This stimulus is referred to as:

Accepted Answer

Supramaximal stimulus

Question 12

During heavy exercise, anaerobic respiration leads to the accumulation of lactic acid. Which equation best represents the conversion of lactic acid back to pyruvate in the liver?

Accepted Answer

$$\mathrm{C_3H_6O_3} + \mathrm{NAD^+} \rightarrow \mathrm{C_3H_4O_3} + \mathrm{NADH} + \mathrm{H^+}$$

Question 13

Which term describes the minimum frequency of stimulation required to produce a fused, sustained contraction in a muscle?

Accepted Answer

Fusion frequency

Question 14

A muscle is lifting a load. Initially, it develops tension without shortening, then shortens to move the load. Which sequence of contractions is occurring?

Accepted Answer

Isometric followed by isotonic

Question 15

Which of the following is NOT a direct cause of secondary (long-term) fatigue in skeletal muscle?

Accepted Answer

Rapid buildup of lactic acid

Question 16

Which term refers to the gradual increase in muscle contraction strength when a muscle is stimulated repeatedly at a low frequency, often seen at the start of exercise?

Accepted Answer

Treppe

Question 17

A muscle cell is exposed to a series of stimuli, each delivered before the previous contraction has fully relaxed. The resulting increase in force is called:

Accepted Answer

Wave summation

Question 18

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

Accepted Answer

Increasing the number of recruited motor units increases muscle tension up to the maximal stimulus.

Question 19

Which scenario best illustrates the concept of mechanical summation in muscle physiology?

Accepted Answer

A muscle receives multiple stimuli in rapid succession, resulting in increased force due to overlapping contractions.

Question 20

A patient experiences muscle weakness after a marathon. Which type of fatigue is most likely responsible, and why?

Accepted Answer

Secondary fatigue, due to depletion of energy reserves

Muscle Physiology: Mechanisms and Types of Skeletal Muscle Contraction

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