Question 1

Which dietary supplement is most likely to contribute to greater skeletal muscle ATP availability in the first few seconds of skeletal muscle contraction?

Accepted Answer

Creatine is a dietary supplement that increases the availability of phosphocreatine in the muscle, which in turn contributes to greater ATP availability during the first few seconds of skeletal muscle contraction. Fatty acids, sports drinks with electrolytes, sugar, and protein do not directly contribute to ATP availability during short-term contractions.

Question 2

Which best describes a role of L-type Ca²⁺ channels in cardiac muscle cells?

Accepted Answer

L-type Ca²⁺ channels in cardiac muscle cells are crucial for preventing tetanic contractions. They allow a controlled and prolonged influx of calcium ions during the plateau phase of the action potential, which ensures that the heart muscle has time to relax between contractions, preventing tetanus and allowing for the rhythmic beating of the heart.

Question 3

Which of the following does NOT correctly describe cardiac muscle cells?

Accepted Answer

Cardiac muscle cells cannot contract in the absence of external calcium. Calcium ions are required for the interaction between the contractile proteins, actin and myosin, to occur, leading to muscle contraction.

Question 4

Which of the following statements is FALSE?

Accepted Answer

This statement is false. Contractile activity of smooth muscle cells requires an increase in intracellular Ca²⁺ concentration, which can be derived from both extracellular and intracellular stores.

Question 5

The name given to the repeating functional units that cause striations in a skeletal muscle myofibril is "sarcomere."

Accepted Answer

The sarcomere is the functional unit of a skeletal muscle myofibril that causes striations.

Question 6

Which is a TRUE statement about excitation-contraction coupling?

Accepted Answer

Calcium-induced calcium release is a mechanism that is indeed present in cardiac muscle cells and in some types of smooth muscle cells. This process involves the entry of a small amount of calcium into the cell, which then triggers the release of more calcium from the sarcoplasmic reticulum, leading to muscle contraction.

Question 7

Which of the following properties of smooth muscle helps us to understand why,as pregnancy advances,women get more and more Braxton-Hicks (smooth muscle)contractions in the uterine wall?

Accepted Answer

Smooth muscle cells contract in response to stretch, which is why as the uterus grows during pregnancy, there is an increase in Braxton-Hicks contractions as the smooth muscle in the uterus is being stretched.

Question 8

If a biopsy of the quadriceps muscles (muscles on the front of the thigh)were taken from gold medal-winning speed skaters in the four following events,which would most likely have the SMALLEST percentage of type 1 muscle fibers?

Accepted Answer

The 500 meters is a sprint event, which requires explosive power and speed. This type of event would primarily rely on type 2 muscle fibers, which are responsible for generating force quickly but fatigue easily. Type 1 muscle fibers, on the other hand, are better suited for endurance activities like long-distance running and would be more prevalent in events like the 10,000 meters. Therefore, the quadriceps muscle biopsy from gold medal-winning speed skaters in the 500 meter event would most likely have the smallest percentage of type 1 muscle fibers.

Question 9

Which of the following is FALSE regarding single-unit smooth muscle cells?

Accepted Answer

Single-unit smooth muscle cells are connected by gap junctions and act as a syncytium, so they do not have individual neuron innervating each individual smooth-muscle cell. Rather, they are innervated by autonomic neurons that release neurotransmitters that diffuse through the tissue and stimulate multiple cells simultaneously.

Question 10

Skeletal muscles are made up of bundles of muscle fibers attached to bone by connective tissue called tendons.

Accepted Answer

Skeletal muscles, also known as voluntary muscles, are attached to bones by tendons, which are made up of connective tissue.

Question 11

Multiunit smooth muscle cells

Accepted Answer

Multiunit smooth muscle cells are characterized by having individual innervation of each cell, unlike single-unit smooth muscle cells which are connected by gap junctions and can contract as a unit.

Question 12

Which is a TRUE statement about smooth muscle?

Accepted Answer

Smooth muscle uses a different mechanism from striated muscle for contraction regulation, involving the phosphorylation of myosin light chain rather than the troponin-tropomyosin complex to control cross-bridge activity.

Question 13

The prolonged electrical depolarization of cardiac muscle cells that occurs during contraction is due primarily to the persistent influx of what ion?

Accepted Answer

The prolonged electrical depolarization of cardiac muscle cells during contraction is due primarily to the persistent influx of calcium ions through voltage-gated calcium channels. This calcium influx triggers the release of more calcium from the sarcoplasmic reticulum, leading to contraction of the cardiac muscle cells. While sodium ions also play a role in the initial depolarization of the cardiac muscle cells, they are rapidly pumped out of the cell, whereas calcium ions continue to enter the cell and contribute to the sustained depolarization.

Question 14

Myasthenia gravis is a collection of muscle disorders that cause muscle fatigue and weakness.What is the major mechanism?

Accepted Answer

Myasthenia gravis is primarily caused by the autoimmune destruction of nicotinic acetylcholine receptors, which are necessary for muscle contractions. This leads to muscle fatigue and weakness.

Question 15

You are trying to design a new drug to painlessly euthanize animals.Your plan is to design a molecule that blocks the action of one of the following pumps so that heart muscle stays contracted and blood movement is stopped.Which would be effective?

Accepted Answer

Blocking the Ca²⁺-ATPase pumps on the sarcoplasmic reticulum would prevent the removal of Ca²⁺ ions from the sarcoplasm, which is required for muscle relaxation. This would lead to sustained muscle contraction and eventual cessation of blood flow. None of the other pumps listed would result in sustained muscle contraction like this.

Question 16

Which of the following statements regarding contraction in skeletal and smooth muscle is TRUE?

Accepted Answer

In skeletal muscle, calcium initiates contraction by binding to troponin on the thin filaments, causing displacement of tropomyosin and exposure of myosin binding sites on actin. In smooth muscle, calcium initiates contraction by binding to calmodulin which activates myosin light-chain kinase, leading to phosphorylation of myosin and activation of contraction.

Question 17

Which of the following choices lists a correct sequence of events following the depolarization of transverse tubules in excitation-contraction coupling in cardiac muscle?

Accepted Answer

The correct sequence starts with calcium ion influx through the sarcolemma, which triggers further calcium release into the cytosol from the sarcoplasmic reticulum. This increase in cytosolic calcium allows actin and myosin to attach, leading to the sliding of thin filaments toward the middle of sarcomeres, causing muscle contraction. This sequence is specific to cardiac muscle, where the initial calcium influx from the extracellular space (through the sarcolemma) is crucial for triggering the larger release of calcium from the sarcoplasmic reticulum, a process known as calcium-induced calcium release (CICR).

Question 18

The force-generating sites in a myofibril are the Z lines.

Accepted Answer

The force-generating sites in a myofibril are the overlapping actin and myosin filaments in the sarcomere, not the Z lines. The Z lines mark the ends of each sarcomere and anchor the thin filaments.

Question 19

Which of these is a major difference between smooth muscle and skeletal muscle?

Accepted Answer

Smooth muscle is regulated by myosin light chain phosphorylation, whereas skeletal muscle is regulated by troponin-tropomyosin complex on actin.

Question 20

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 Sarah's muscles,how are Priya's most likely to differ?

Accepted Answer

Marathon running requires the utilization of oxidative metabolism for energy production, so Priya's muscles would be expected to have more mitochondria in her type 1 and 2A muscle fibers to facilitate this process. Glycogen storage in type 2X fibers would be more important for sprinting (A), and myoglobin content typically increases in type 1 fibers, so Priya's type 1 fibers would likely have more myoglobin (C). While muscle fiber diameter can increase with training, there's no reason to assume that Priya's type 2X fibers would be larger in diameter (D). It's also not clear that Priya would necessarily have a greater proportion of type 2 fibers than Sarah (E).

Quiz 9: Muscle

Which dietary supplement is most likely to contribute to greater skeletal muscle ATP availability in the first few seconds of skeletal muscle contraction?

Which best describes a role of L-type Ca²⁺ channels in cardiac muscle cells?

Which of the following does NOT correctly describe cardiac muscle cells?