Muscular System Review_week of Nov. 16

Which factors will affect the force or intensity of a muscle contraction?

• the frequency of nerve signals received by the muscle

• the number of myofibers (muscle cells) activated at one time

• how much the sarcomere and myofibril shorten when they contract

• how many sarcomeres in one myofiber shorten

Answer explanation

Muscles follow the All-or-None law so sarcomeres will always shorten as much as they can when stimulated. Also, all the sarcomeres in a myofibril should be triggered at the same time due to how action potentials work (something we'll talk more about in the nervous system). This explains the two wrong options.

Muscles experience fatigue when they run out of (a)  

Answer explanation

Since oxygen is required for the maximum production of ATP in the mitochondria, either ATP or oxygen would work for this answer. Either way, your muscles are running out of energy! Give them a rest!

When you lift heavy weights or do resistance type exercises, how does the anatomy of your muscle change?

• increase mitochondria

• increase blood vessels

• increase actin and myosin proteins

• increase nuclei

Answer explanation

Lifting weights tells your muscles they need to be stronger. Stronger muscle requires more contractile power, which requires more actin and myosin proteins. The increased nuclei assist in increased protein production.

When you engage in cardio or aerobic exercises, how does the anatomy of your muscle change?

• increase mitochondria

• increase blood vessels

• increase actin and myosin proteins

• increase nuclei

Answer explanation

Doing aerobic activities tells your muscles they need to have more endurance. In order for muscles to not fatigue as quickly, they need to be able to produce more energy at a time. So they make more mitochondria (ATP production factories) and increase the amount of oxygen and glucose delivered to those mitochondria by building more blood vessels.

When muscles shrink due to a lack of use (or poor nutrition or chronic disease), it is called...

• atrophy

• hypertrophy

• sarcophagy

• hypotrophy

Answer explanation

"A-" means 'without' and "-troph" refers to nutrition. So atrophy means "without nutrition", referring to the fact that atrophied muscle looks small, shrunken, and starved of strength. Use it or lose it, folks!

Muscles are able to...

• pull

• push

• pull or push

Answer explanation

Since getting shorter is the only thing muscles can actively do (lengthening back out to their original size is a passive process), they're only able to PULL on whatever they're attached to.

Olympic marathoners probably have a higher percentage of (a)   twitch muscle fibers.

Answer explanation

Slow twitch muscle fibers have greater endurance than fast twitch fibers, so Olympic marathoners were most likely born with a greater percentage of those muscle cells, making them better suited to long-distance, endurance running. Most of us mere mortals have a equal amount of each.

Which hormone has an effect on our muscle performance when released?

• adrenaline

• melatonin

• calcitonin

• oxytocin

Answer explanation

Adrenaline is our fight or flight hormone, increasing our muscles endurance by allowing for more oxygen and sugar to be delivered to the cells and increasing its apparent strength by shutting off pain receptors, allowing us to demand more from our muscles than normal.

Explain the results of this graph.

Answer explanation

The breast muscles are required for flight. Since chickens don't fly, those muscles don't have as many mitochondria because they're not frequently used. Pigeons and ducks, on the other hand, fly often so those muscles need to have greater endurance, hence more mitochondria for energy.

Working out will increase the number of muscle fibers (aka: muscle cells) you have in your muscles.

• True

• False

Answer explanation

You are essentially born with all the muscle cells you're going to have (as far we know). So working out will not increase the number of muscle cells you have, but it will increase the SIZE or DIAMETER of the muscle cells you have as well as the amount of connective tissue you may have around the muscles.