Question 1

Increasing the number of recruited motor units in a muscle increases its force or strength of contraction.

Accepted Answer

Increasing the recruitment of motor units within a muscle can increase the overall force or strength of contraction. This is due to the fact that more muscle fibers are being activated and contributing to the contraction, resulting in a greater force output.

Question 2

A motor unit is a single muscle plus all the motor neurons that innervate it.

Accepted Answer

A motor unit consists of a single motor neuron and all the muscle fibers it innervates, not a single muscle plus all the motor neurons that innervate it.

Question 3

Gradation of muscle contraction can be accomplished by stimulating variable portions of each motor unit.

Accepted Answer

Gradation of muscle contraction is accomplished by recruiting more or fewer motor units and by varying the frequency of stimulation of those motor units, not by stimulating variable portions of each motor unit, as each motor unit is either fully activated or not at all (all-or-none principle).

Question 4

Joints serve as fulcrums for muscle action.

Accepted Answer

Joints are the points at which bones articulate and provide leverage for muscle action. They serve as fulcrums for the movement of the body.

Question 5

ATP expenditure is required for both contraction and relaxation of a muscle fibre.

Accepted Answer

Muscle contraction requires ATP to power the movement of myosin heads along actin filaments. During relaxation, ATP is required to actively transport calcium ions back into the sarcoplasmic reticulum, a process that allows the muscle to relax and prepare for another contraction.

Question 6

With twitch summation, the muscle fibre is stimulated so rapidly that it does not have an opportunity to return to resting potential between stimuli.

Accepted Answer

The answer of With twitch summation, the muscle fibre is...

Question 7

Denervated muscle fibres become progressively smaller and their content of actin and myosin decreases.

Accepted Answer

Denervation leads to muscle atrophy, which involves the decrease in muscle fibre size and content of contractile proteins such as actin and myosin.

Question 8

Tetanus occurs when a muscle fibre is stimulated so rapidly that it is not allowed to relax between stimulations, resulting in a smooth, sustained contraction.

Accepted Answer

This is a accurate description of tetanus, which is also known as lockjaw. It is caused by toxins produced by the bacterium Clostridium tetani, which interfere with the normal function of inhibitory neurons in the spinal cord, leading to excessive muscle contractions. These contractions can be so strong that they cause fractures or other serious injuries. Tetanus can be prevented through vaccination and prompt medical treatment in case of injury with potentially contaminated objects.

Question 9

A skeletal muscle produces motion by pulling the origin toward its insertion.

Accepted Answer

Skeletal muscle produces motion by pulling its insertion towards its origin, not the other way around. The origin is typically stationary, while the insertion moves.

Question 10

The metabolic capability of a muscle fibre can affect the degree of tension it can develop.

Accepted Answer

The metabolic capability of a muscle fibre determines its ability to produce energy which, in turn, affects the degree of tension it can develop during contraction. Therefore, the statement is correct, making option A the correct answer.

Question 11

In an isotonic contraction, only 25 percent of the energy consumed is realized as external work, and the remaining 75 percent is converted to heat.

Accepted Answer

This statement is true. In isotonic contractions, the muscle shortens against a constant load, and only a portion of the energy consumed is converted to external work. The majority of the energy is converted to heat, which is why muscles can sometimes feel warm or hot after exercise.

Question 12

Muscle tension does not develop in isometric contractions.

Accepted Answer

Muscle tension does in fact develop in isometric contractions, as the muscle is generating force against an immovable object or resistance without changing its length.

Question 13

Muscles that have a fine degree of control have small motor units.

Accepted Answer

Muscles that have a fine degree of control (such as those in the fingers) require small motor units in order to achieve precise movements. Small motor units consist of fewer muscle fibers and are controlled by fewer nerve fibers, allowing for more precise control.

Question 14

The shorter a muscle fibre is before the onset of a contraction, the greater the force that can be developed upon the subsequent contraction because the thin filaments are already partially slid inward.

Accepted Answer

The force a muscle can develop during a contraction is actually greater when the muscle fiber starts from a slightly stretched position rather than a shortened one. This is because the optimal overlap between actin and myosin filaments (thin and thick filaments, respectively) for force generation is not achieved when the fiber is too short.

Question 15

More tension is developed during twitch summation than during a single twitch because the duration of elevated cytosolic Ca²⁺ concentration increases during summation, thus increasing the availability of cross-bridge binding sites.

Accepted Answer

During twitch summation, the frequency of stimulation is increased, leading to an increase in cytosolic Ca²⁺ concentration and the lengthening of the duration of elevated Ca²⁺ levels. This increase in duration of elevated Ca²⁺ levels allows for more cross-bridge cycling and increased tension development. Therefore, more tension is developed during twitch summation than during a single twitch.

Question 16

Summation events result from increasing amounts of cytoplasmic calcium levels.

Accepted Answer

Summation events occur when there is an increase in cytoplasmic calcium levels, which leads to the activation of more muscle fibers and ultimately results in a stronger contraction.

Question 17

The larger the motor units within a muscle, the more precisely controlled the gradations of contraction.

Accepted Answer

The opposite is actually true - smaller motor units allow for more precise control over gradations of contraction. Larger motor units are used for more forceful contractions.

Question 18

The skeletal muscle shortens during concentric, isotonic contraction.

Accepted Answer

During concentric, isotonic contraction, the muscle fibers shorten and the muscle shortens as a whole, resulting in movement at the joint.

Question 19

Ligaments attach muscles to bones.

Accepted Answer

Ligaments attach bones to bones, while tendons attach muscles to bones.

Question 20

All muscle-lever systems work at a mechanical disadvantage.

Accepted Answer

Some muscle-lever systems in the body work at a mechanical advantage, allowing for greater force production, while others work at a mechanical disadvantage to increase speed or range of motion.

Quiz 7: Muscle Physiology