Question 1

Without the protein myosin, what structures would also be missing in a muscle?

Accepted Answer

Myosin is a component of thick filaments in muscles. Without myosin, the thick filaments would not be able to function properly and muscle contraction would not occur. Ribosomes and mitochondria are not directly involved in muscle contraction, while thin filaments are composed of actin, not myosin.

Question 2

Into what units are the myofibrils of skeletal muscle organized?

Accepted Answer

The myofibrils of skeletal muscle are organized into sarcomeres, which are the basic functional units of skeletal muscle contraction. Sarcomeres are made up of thin and thick filaments that slide past each other, resulting in muscle contraction. A discs, Z discs, and antagonistic pairs are also components of skeletal muscle, but do not organize the myofibrils into functional units.

Question 3

Arm and leg muscles are arranged in antagonistic pairs. How does this affect their functioning?

Accepted Answer

Antagonistic muscle pairs work together to produce opposing movements, such as flexing and extending a joint. For example, the biceps and triceps in the arm are an antagonistic pair - the biceps flex the elbow while the triceps extend it. This allows for more precise control of movements and a wider range of motion.

Question 4

True or false: The larger muscle fibers found in males account for the fact that males tend to be, on average, stronger than females.

Accepted Answer

The larger muscle fibers found in males contribute to their greater strength compared to females on average. Testosterone, which is present in higher levels in males, also plays a role in muscle growth and development.

Question 5

In general, what hormone is produced in greater quantities in males that allows them to have a greater muscle mass than females?

Accepted Answer

Testosterone is the hormone produced in greater quantities in males that allows them to have a greater muscle mass than females. Testosterone is an androgen hormone that helps to stimulate muscle growth and increase muscle strength. Females produce much smaller amounts of testosterone in their ovaries and adrenal glands, which is why they have less muscle mass and strength compared to males. Adrenaline (A) and growth hormone (D) can also contribute to muscle growth, but they are not produced in greater quantities in males compared to females. Estrogen (C) is a female sex hormone that can actually inhibit muscle growth, which is why males typically have greater muscle mass than females.

Question 6

When working out with his wife, Ed has noticed he has to drink much more Gatorade than his wife does following their workouts. What fact could explain this difference in their workout requirements?

Accepted Answer

Females tend to use more fat as an energy source during exercise, whereas males tend to rely more on glucose. This means that females typically need less glucose replenishment in the form of sports drinks like Gatorade.

Question 7

Which muscle component is smallest?

Accepted Answer

Myosin filaments are the smallest muscle component, measuring about 1-2 micrometers in diameter, whereas myofibrils can reach up to several micrometers in diameter, sarcomeres can be several micrometers long, and muscle fibers can be several millimeters in length.

Question 8

How does a sarcomere shorten using the sliding filament mechanism of muscle contraction?

Accepted Answer

Actin and myosin filaments do not actually shorten during muscle contraction. Instead, they slide past each other, which shortens the overall length of the sarcomere.

Question 9

Which type of muscle in humans is involved in voluntary body movements?

Accepted Answer

Skeletal muscles are attached to bones and responsible for voluntary body movements. Cardiac muscles are found in the heart and are responsible for involuntary contractions, while smooth muscles are found in internal organs and blood vessels and are also responsible for involuntary actions. Endothelial cells are a type of cell lining the blood vessels and are not muscle cells.

Question 10

If healthy men have a range of body fat from 3 to 29% and healthy women have a range of body fat from 12 to 32%, what would you predict for the sex of an individual having 20% body fat?

Accepted Answer

The individual's sex can't be predicted from body fat percentage because 20% falls within the healthy range for both men (3-29%) and women (12-32%).

Question 11

What happens to a sarcomere when muscle contraction occurs?

Accepted Answer

During muscle contraction, the sarcomere shortens due to the sliding of actin filaments over myosin filaments, bringing the Z lines closer together.

Question 12

What type of muscle fibers will be found in large percentages in the leg muscles of a person who excels at weight lifting but does not do well at running marathons?

Accepted Answer

Weight lifting requires short bursts of intense effort, which is dependent on fast-twitch muscle fibers. These fibers have high levels of energy production and fatigue quickly, but can generate high levels of force. Running marathons, on the other hand, requires a lot of endurance, which is only possible with slow-twitch muscle fibers. These fibers are designed for long-term energy production and do not fatigue easily. Therefore, a person who excels at weight lifting but not at marathon running is likely to have a higher percentage of fast-twitch muscle fibers in their leg muscles.

Question 13

Teri brings her husband, Liam, with her to the gym and signs them both up for a one-hour aerobics class. After 20 minutes, Liam is visibly fatigued, even though he is a regular at the gym, lifting weights and playing basketball. What might explain why he is fatigued while his wife, although working hard, is not struggling?

Accepted Answer

Research has shown that females tend to use more fat for energy during endurance exercises, allowing them to maintain physical activity for longer periods of time compared to males who rely more on carbohydrates for energy. This could explain why Teri's husband is fatigued while Teri, who is also working hard, is not struggling.

Question 14

Mary is a long-distance runner and trains regularly. Recently, Mary and her husband have unsuccessfully tried to conceive a child. To improve her chances of getting pregnant, why does her doctor suggest that she should stop training?

Accepted Answer

Low levels of body fat may cause menstruation to cease, which can make it more difficult for Mary to conceive. Stopping training may help increase body fat levels and allow for regular menstruation to resume, improving her chances of becoming pregnant.

Question 15

Why does skeletal muscle have a striated appearance?

Accepted Answer

Skeletal muscle has a striated appearance due to the regular arrangement of myofibrils, which are the contractile units of muscle cells. The myofibrils contain alternating light and dark bands called sarcomeres, which give the muscle its striped appearance.

Question 16

When a person dies, muscles become rigid and fixed in position. This is a condition known as rigor mortis. Why does rigor mortis occur?

Accepted Answer

Rigor mortis occurs because ATP is no longer available to release the myosin heads from the actin filaments, which causes the muscles to become stiff and fixed in position. Without ATP, the myosin heads can no longer detach from the actin filaments after they have formed cross-bridges, and thus muscle fibers cannot relax.

Question 17

Studies have demonstrated that in some cases, female marathon runners don't exhibit a normal menstrual cycle. What fact could explain this condition in female runners?

Accepted Answer

This condition is often seen in female runners who do not have enough body fat, which can disrupt hormonal balance and lead to a lack of menstruation.

Quiz 21: Human Sex Differences: Endocrine, Skeletal, and Muscular Systems