Question 1

Which of these occurs during an isometric contraction of a skeletal muscle?

Accepted Answer

During an isometric contraction, the muscle generates force without changing its length significantly. This means that the sarcomere length does not change, and the thick and thin filaments do not slide past each other. However, the tension generated by the muscle can still be measured.

Question 2

Which of the following statements regarding whole-muscle contraction is TRUE?

Accepted Answer

The answer of Which of the following statements regarding whole-muscle...

Question 3

The optimal length (Lₒ) of a skeletal muscle cell is

Accepted Answer

The optimal length (Lₒ) of a skeletal muscle cell is the length at which the muscle can generate its maximum tetanic tension. This is because at this length, there is optimal overlap between the thick and thin filaments in the sarcomeres, allowing for maximal cross-bridge formation and force generation. At other lengths, the amount of overlap is suboptimal, leading to decreased force production.

Question 4

The muscles in your fingers have a predominance of fast-glycolytic fibers,whereas the muscles of your feet have a predominance of slow-oxidative fibers.Which of the following statements accurately describes their differences?

Accepted Answer

The answer of The muscles in your fingers have a...

Question 5

When a muscle has been repeatedly contracting at a moderate intensity for an extended period of time (more than a few minutes),what is the primary source of ATP?

Accepted Answer

When a muscle has been repeatedly contracting at a moderate intensity for an extended period of time, the primary source of ATP is oxidative phosphorylation, which involves the use of oxygen in the mitochondria to produce ATP through the electron transport chain. This process is more efficient than glycolysis or creatine phosphate breakdown and can sustain muscle contraction for a longer period of time.

Therefore, options A, B, D, and E are incorrect as they do not provide the most efficient source of ATP for sustained muscle contraction.

Question 6

In the first few seconds of skeletal muscle contraction,what is the main mechanism by which ATP is replenished?

Accepted Answer

During the first few seconds of skeletal muscle contraction, the main mechanism by which ATP is replenished is the transfer of energy and phosphate from creatine phosphate to ADP. This process, known as the creatine phosphate system, provides a rapid source of ATP for immediate use by the muscle. Glycolysis and oxidative phosphorylation also play a role in providing energy during sustained muscle contraction. However, these processes take longer to ramp up and are not as immediate as the creatine phosphate system. Myoglobin does not catalyze the production of ATP, but rather helps to store oxygen within the muscle fibers. Fatty acid oxidation takes place in the mitochondria and provides ATP for longer duration activities.

Question 7

Which of the following statements regarding skeletal muscle contraction is true?

Accepted Answer

During every muscle contraction, tension is developed in the muscle. The tension produced by the muscle may or may not be enough to lift the load or move the body part, depending on the type of contraction. In isometric contractions, the muscle length remains constant, while in isotonic contractions, the muscle changes length. In a lengthening contraction, the tension exerted by the muscle is less than the load on the muscle, while in a shortening contraction, the tension exerted by the muscle exceeds the load on the muscle. Cross-bridges cycle faster during isotonic contractions than during isometric contractions.

Question 8

During an isometric twitch in a skeletal muscle

Accepted Answer

During an isometric twitch, the tension generated by the muscle remains constant as the sarcomeres do not significantly shorten. Therefore, the load on the muscle may exceed the tension generated, and the muscle does not shorten as a whole, nor do the H zones shorten. Tetanus can only occur during sustained contractions, not during twitches.

Question 9

What is the best description of a tetanic contraction in a skeletal muscle cell?

Accepted Answer

In a tetanic contraction, multiple action potentials in the motor neuron cause a sustained contraction. This occurs because the frequency of action potentials causes the muscle cell to not fully relax before the next contraction, resulting in a more sustained contraction.

Question 10

Unlike humans,cows eat all day.They spend hours and hours chewing with very little rest from the task in a 24-hour period.The food they eat (grass)is difficult to break down,requiring a lot of chewing.Understanding the endurance required for these chewing muscles,what fiber type would you expect to be predominant in their chewing muscles?

Accepted Answer

Type 1 muscle fibers are also known as slow-twitch fibers and are ideal for prolonged, low-intensity activities such as chewing. Cows require a lot of endurance for their daily chewing task, so it is expected that their chewing muscles would have a higher proportion of Type 1 muscle fibers.

Question 11

How is the length of a skeletal muscle cell related to the force it can generate?

Accepted Answer

The length-tension relationship of skeletal muscle states that the force generated by the muscle is dependent on its length at the time of contraction. The optimal force generation occurs when the muscle is at an intermediate length, where there is maximum overlap between the actin and myosin filaments within the muscle fibers. When the muscle is too stretched or too contracted, the filaments have less overlap, resulting in reduced force generation. Therefore, choice E is the correct answer.

Question 12

Myasthenia gravis is an autoimmune disease in which the immune system gradually destroys the receptors for acetylcholine at the neuromuscular junction.Which of the following drugs might initially be useful in treating the symptoms of this disease?

Accepted Answer

Myasthenia gravis is a disease where the immune system destroys the receptors for acetylcholine, leading to muscle weakness and fatigue. Acetylcholinesterase inhibitors can be used to increase the levels of acetylcholine in the synaptic cleft, leading to improved muscle contraction and reduced symptoms. Therefore, option A, a drug that inhibits acetylcholinesterase, might initially be useful in treating the symptoms of this disease. The other options are not suitable for treating myasthenia gravis, as they either inhibit the release of or block the actions of acetylcholine, which would exacerbate the symptoms.

Question 13

Sarah is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest.Priya is a marathon runner who specializes in long,steady runs.Compared to Priya,Sarah is likely to have

Accepted Answer

Sprinters like Sarah typically have leg muscles with a larger diameter due to the hypertrophy of type II muscle fibers, which are responsible for quick and powerful movements.

Question 14

Which of the following statements regarding myosin in skeletal muscle is TRUE?

Accepted Answer

Myosin is an ATPase enzyme, which means it can break down ATP into ADP and phosphate to release energy for muscle contraction. Option A is incorrect because myosin cross-bridge heads contain only one binding site for actin, not for tropomyosin. Option C is incorrect because the rate of ATP hydrolysis varies with the type of skeletal muscle fiber. Option D is incorrect because the myosin cross-bridge heads in a thick filament are oriented and rotate in opposite directions. Option E is incorrect because troponin, not tropomyosin, covers the binding site on the actin molecule until Ca²⁺ binds to troponin to move tropomyosin away and expose the binding site.

Question 15

Tetanus toxin inhibits acetylcholinesterase activity.What will a person suffering from tetanus toxin poisoning look like?

Accepted Answer

Tetanus toxin does not inhibit acetylcholinesterase; instead, it prevents the release of inhibitory neurotransmitters in the central nervous system, leading to uncontrolled muscle contraction. This results in a tense, fully contracted state of the muscles, not the inhibition of acetylcholinesterase or its direct effects as implied in the question.

Question 16

Compared to type 1 (slow oxidative)skeletal muscle fibers,how are type 2X (fast-glycolytic)skeletal muscle fibers different?

Accepted Answer

Type 2X fibers have less abundant mitochondria, less myoglobin, and a smaller diameter than type 1 fibers. However, they have a higher capacity for glycolysis, which allows them to generate ATP more quickly but also leads to quicker fatigue. Type 2X motor units contain more fibers per alpha motor neuron, which contributes to their greater force production capabilities.

Question 17

Which of these would increase the tension generated in a skeletal muscle?

Accepted Answer

Increasing the frequency of firing in alpha motor neurons innervating the muscle would lead to an increase in the number of muscle fibers contracting at the same time, resulting in an increase in muscle tension. This is known as temporal summation or frequency summation. Stretching the muscle to very long lengths can also increase muscle tension, but this is limited by the length-tension relationship of the muscle fibers. Resting the muscle for several weeks would actually decrease muscle tension due to atrophy of the muscle fibers. Switching off fast-glycolytic motor units and activating slow-oxidative motor units would lead to a decrease in muscle tension since slow-oxidative fibers generate less force than fast-glycolytic fibers. Increasing the amplitude of action potentials in the alpha motor neurons that innervate the muscle would not have a significant effect on muscle tension.

Question 18

Which of the following is NOT a determinant of whole-muscle tension?

Accepted Answer

While the proportion of the muscle fibers within each motor unit that are contracting at any given time can affect the smoothness and precision of muscle movements, it is not a determinant of whole-muscle tension, which is the force generated by the overall muscle contraction. The determinants of whole-muscle tension are A) the number of muscle fibers contracting, B) the tension produced by each contracting fiber, C) the numbers of motor units recruited, and D) the frequency of motor neuron stimulation.

Question 19

Which of the following statements regarding skeletal muscle is TRUE?

Accepted Answer

A given skeletal muscle fiber will contract if excitatory synaptic inputs sufficiently exceed inhibitory synaptic inputs on the motor neuron that innervates that fiber and the motor neuron fires an action potential. This action potential triggers the release of calcium ions from the sarcoplasmic reticulum within the muscle fiber, leading to muscle contraction. Gap junctions and pacemaker activity are not characteristic of skeletal muscle, and inhibitory motor neurons can only inhibit, rather than promote, skeletal muscle contraction.

Question 20

Sarah is a girl with dreams of becoming an Olympic marathon runner.She just learned that she has a rare genetic mutation and does not produce functional creatine phosphate.What portion of Sarah's marathon experience will be effected?

Accepted Answer

Creatine phosphate is crucial for the rapid regeneration of ATP in muscles, primarily during the first few seconds of high-intensity exercise. It provides an immediate source of energy for muscle contractions at the start of an activity. In marathon running, which relies more on aerobic metabolism after the initial burst, the lack of functional creatine phosphate would mainly affect Sarah's performance at the very beginning of her run.

Quiz 9: Muscle