Question 1

You are a lab technician staining sections of skeletal muscle using a stain that binds to mitochondria.The tissue comes from leg biopsies of two patients: a professional weight lifter and a competitive long distance runner.You realize the slides are unlabeled.How might you determine which slide belongs to which patient?

Accepted Answer

Competitive long distance runners have a greater number of mitochondria per cell compared to weight lifters due to their high energy demand during endurance activities. Mitochondria are responsible for energy production in cells, and thus more mitochondria per cell indicates a higher energy demand. Red muscle fibers contain more mitochondria than white muscle fibers, and thus the slide with more red muscle and more mitochondria per cell would belong to the long distance runner. The other options are incorrect as they do not provide a clear indication of which slide belongs to which patient based on mitochondrial staining.

Question 2

In a class 1 lever, the fulcrum is between the load and force arms.A class 1 lever is used when

Accepted Answer

Tilting your head back is an example of a class 1 lever because the fulcrum (the joint at the base of your skull) is between the load (the weight of your head) and the force arm (the muscles in the back of your neck that lift your head).

Question 3

Cartilage

Accepted Answer

Cartilage is a principal component of the embryonic skeleton in humans, providing a template for bone development.

Question 4

You come across several invertebrate organisms crawling through the sand.You notice that they have a soft body wall, and when you dissect one, you see that it has no rigid structures inside the body.This organism most likely

Accepted Answer

The absence of rigid structures inside the body and a soft body wall suggest that the organism uses a hydrostatic skeleton to move. Hydrostatic skeletons rely on fluid pressure to provide support and enable movement. In contrast, options A, B, and E involve some type of rigid structure, which is inconsistent with the observations of the organism. Option C describes an exoskeleton, which is a rigid external structure rather than an internal one.

Question 5

Refer to the figure showing a sarcomere when it is relaxed.  When the muscle contracts, _______ will become more narrow in the sarcomere.

Accepted Answer

During muscle contraction, the sarcomere shortens as the thin filaments (actin) slide over the thick filaments (myosin). This results in a reduction in the width of both the I band (the region containing only actin filaments) and the H zone (the region containing only myosin filaments). Therefore, both the I band and the H zone become more narrow in the sarcomere during muscle contraction.

Question 6

A dead body will undergo rigor mortis, a condition in which muscles stiffen and do not relax.This is a result of

Accepted Answer

Rigor mortis occurs due to a lack of ATP production, preventing the detachment of myosin from actin filaments, leading to muscle stiffness.

Question 7

A pair of closely related bird species includes one that migrates long distances over the course of months and another that has evolved near-flightlessness on its island home.What might you expect to find when comparing the breast muscles (used for flight) of these species?

Accepted Answer

The migrant species would have relatively larger amounts of red muscle because this type of muscle is better adapted for sustained, aerobic activity required for long-distance flight compared to white muscle fibers. The near-flightless island species would not have as much need for red muscle since they do not fly as much or as far.

Question 8

You are a graduate student researching the function of muscles.You induce a mutation that eliminates titin.Which is the most likely direct outcome for a mouse with this mutation?

Accepted Answer

Titin is a protein that plays a crucial role in maintaining the structure of sarcomeres, the basic unit of muscle contraction. Without titin, sarcomeres would not be able to hold their structure and the muscle would not function properly. This would likely result in muscle weakness or inability to contract effectively, leading to various functional deficits. Therefore, choice D (sarcomeres will not hold their structure) is the most likely direct outcome of eliminating titin.

Question 9

Gap junctions are made up of specific proteins called connexin.If _______ muscle cells were unable to make connexin, then _______.

Accepted Answer

Gap junctions play a crucial role in the synchronized depolarization of cardiac cells and the coordination of contractions. Without connexin proteins, the cells would be unable to form gap junctions and the heart would not function normally. Therefore, if cardiac muscle cells were unable to make connexin, the heart could not function normally.

Question 10

ATP is supplied to your muscles through several systems.As you exercise, where does the ATP you use come from, in order from most accessible to most slowly produced?

Accepted Answer

The most immediately accessible source of ATP is stored ATP and creatine phosphate. This can be used for short bursts of activity. As this is depleted, the next source is glycolysis in the cytoplasm, which is a quicker way to produce ATP than oxidative metabolism in the mitochondria. However, glycolysis produces ATP at a slower rate than stored ATP and creatine phosphate. Finally, as exercise continues, the body switches to oxidative metabolism in the mitochondria, which produces ATP more slowly, but can sustain ATP production for a longer period of time.

Question 11

World-class sprinters running at top speed are most likely to _______ in the skeletal muscles used for running by the end of 30 seconds.

Accepted Answer

Sprinting at top speed primarily relies on the anaerobic breakdown of glucose, which rapidly produces ATP through glycolysis. This process relies on preformed ATP and creatine phosphate, which can sustain maximal effort for only a short time (about 30 seconds). After this point, the muscles will start to fatigue and the sprinters will slow down. While sprinters do have some reserve of creatine phosphate, it is limited and will eventually be depleted. Oxygen-dependent oxidative metabolism (choice E) is not the primary source of ATP production during short-term, high-intensity activities like sprinting.

Question 12

Which statement about neuromuscular junctions is true?

Accepted Answer

A single motor neuron can indeed innervate more than one skeletal muscle cell, forming a motor unit. This allows for coordinated contraction of multiple muscle fibers.

Question 13

While lifting weights at the gym, you pause to use your fingertip to adjust the volume on your iPod.Which statement about the muscle contractions involved in adjusting the volume is true?

Accepted Answer

The same number of action potentials is required to stimulate a muscle fiber regardless of the muscle's location or size. This is because the process of muscle fiber activation (excitation-contraction coupling) is fundamentally the same across skeletal muscles.

Question 14

Bone is continuously remodeled by _______ that resorb bone and release calcium into the extracellular fluid, and _______ that lay down new bone.

Accepted Answer

Osteoclasts are bone cells that are responsible for bone resorption, which releases calcium into the extracellular fluid. Osteoblasts are bone cells that produce new bone tissue, which replaces the resorbed bone. Therefore, option A is the correct answer. Options B, C, D, and E do not accurately describe the process of bone remodeling.

Question 15

A hiker is bitten by a venomous snake.The venom prevents the release of calcium from the sarcoplasmic reticulum.Which symptom might the patient exhibit?

Accepted Answer

Calcium release from the sarcoplasmic reticulum is crucial for muscle contraction because it binds to troponin, allowing actin and myosin to interact. If the venom prevents calcium release, the patient's muscles will not be able to contract.

Question 16

Which feature distinguishes a smooth muscle cell from a skeletal muscle cell?

Accepted Answer

Gap junctions allow for the spread of action potentials between cells, which is a feature unique to smooth muscle cells. Skeletal muscle cells do not have gap junctions, and therefore rely on neuromuscular junctions for communication with the nervous system. The other options listed are not accurate features that distinguish smooth muscle from skeletal muscle.

Question 17

Flexor and extensor muscles work _______ to operate a joint.

Accepted Answer

Flexor and extensor muscles work antagonistically to operate a joint. This means that when one group of muscles contracts (the flexors), the other group (the extensors) must relax in order for movement to occur. For example, when you bend your elbow (flexion), the biceps muscle contracts (shortens) and the triceps muscle relaxes (lengthens). When you extend your elbow (bringing it back to a straight position), the triceps contract and the biceps relax. It's this antagonistic relationship between flexors and extensors that allows for controlled, coordinated movement.

Question 18

A mutation results in a developmental defect that stops the ionic current from flowing from cell to cell in cardiac muscle.Which structure(s) is/are most likely defective as a result of this mutation?

Accepted Answer

Gap junctions are the structures responsible for allowing the flow of ionic current from cell to cell in cardiac muscle. If there is a mutation that stops the flow of current, it is likely that the gap junctions are defective. Sarcomeres, titin, actin and neuromuscular junctions are not directly involved in the ionic flow between cardiac muscle cells.

Question 19

Most of the compact bone in mammals is composed of concentric bony cylinders with a central canal called _______ systems.This type of bone _______.

Accepted Answer

The Haversian system, also known as the osteon, is the structural unit of compact bone and consists of concentric bony cylinders with a central canal for blood vessels and nerves. This type of bone is able to withstand compression forces. Choices A, C, D, and E do not accurately describe compact bone or its properties.

Quiz 47: Musculoskeletal Systems