Deck 9: Skeletal Muscle: Structure and Function

Question 1

Which of the following events in muscle contraction is the first to occur chronologically?

A) The T-tubules depolarize, causing calcium to be released from the sarcoplasmic reticulum.
B) Calcium is resequestered (taken up) into the sarcoplasmic reticulum.
C) Tropomyosin moves, exposing the actin active sites.
D) The innervating alpha-motor neuron has an action potential.
E) The binding of acetylcholine causes a skeletal sarcolemma to have an action potential.

Answer 1

D

Question 2

Which of the following has been shown to cause muscle fatigue?

A) the accumulation H⁺
B) the accumulation of ATP
C) the accumulation of Na⁺
D) the accumulation of muscle glycogen

Answer 2

A

Question 3

Which of the following events in muscle contraction is the last to occur chronologically?

A) The T-tubules depolarize, causing calcium to be released from the sarcoplasmic reticulum.
B) Calcium is resequestered (taken up) into the sarcoplasmic reticulum.
C) Tropomyosin moves, exposing the actin active sites.
D) The innervating alpha-motor neuron has an action potential.
E) The binding of acetylcholine causes a skeletal sarcolemma to have an action potential.

Answer 3

B

Question 4

The cell membrane around muscle is called the

A) soma.
B) plasma membrane.
C) mucous membrane.
D) sarcolemma.

Question 5

The layer of connective tissue that surrounds the outside of skeletal muscle (i.e., just below the fascia) is called the

A) epimysium.
B) perimysium.
C) endomysium.
D) basement membrane.

Question 6

The formation of cross-bridges in the contractile process in skeletal muscle is

A) potassium binding to myosin.
B) calcium binding to tropomyosin.
C) calcium binding to troponin.
D) ATP binding to the myosin cross-bridges.

Question 7

Calcium is stored in muscle within the

A) Golgi organs.
B) H zone.
C) sarcoplasmic reticulum.
D) sarcolemma.

Question 8

A successful endurance athlete would likely have ________________ compared to a sedentary person.

A) a higher percentage of glycolytic fibers
B) a higher percentage of type I fibers
C) a higher percentage of fast-twitch fibers
D) the same percentage of slow-twitch and fast-twitch fibers

Question 9

Type IIx fibers

A) contain a high concentration of aerobic enzymes.
B) are very energy efficient.
C) have high specific tension.
D) exhibit a high level of fatigue resistance.

Question 10

A muscular contraction that results in a movement of body parts is called a(n)

A) isometric contraction.
B) static contraction.
C) isotonic or dynamic contraction.
D) muscle twitch.

Question 11

The amount of force exerted during muscular contraction is dependent on the

A) type of motor units recruited and nothing else.
B) type of motor units recruited, the initial length of the muscle, and the nature of the neural stimulation.
C) length of the muscle fibers only.
D) nature of the neural stimulation only.

Question 12

The motor neuron and all the muscle fibers it innervates are called a motor

A) junction.
B) unit.
C) end plate.
D) nerve.

Question 13

Skeletal muscle fibers that contain large numbers of mitochondria and myoglobin could be classified as

A) type I fibers
B) type IIa fibers
C) either type I or type IIa
D) type IIx

Question 14

The site where the motor neuron and muscle cell meet is called the

A) end-plate potential.
B) motor unit.
C) sarcolemma.
D) neuromuscular junction.

Question 15

The two principal contractile proteins found in skeletal muscle are

A) actin and troponin.
B) actin and myosin.
C) troponin and tropomyosin.
D) myosin and tropomyosin.

Question 16

The breakdown of ATP in muscle is accomplished via the enzyme

A) lactate dehydrogenase.
B) succinate dehydrogenase.
C) ATPase.
D) phosphofructokinase.

Question 17

Satellite cells

A) contribute to muscle growth by dividing and contributing mitochondria to existing muscle fibers.
B) reside below the sarcolemma.
C) are differentiated cells that can turn into muscle fibers.
D) are undifferentiated cells that play a key role in muscle growth and repair.

Question 18

During the initial period of disuse (i.e., 2 days), muscle atrophy is predominantly due to

A) decreased protein synthesis.
B) increased protein breakdown.
C) both a decreased protein synthesis and increased protein breakdown.

Question 19

Fast-twitch fibers contain a relatively

A) large number of mitochondria and low ATPase activity.
B) small number of mitochondria and low ATPase activity.
C) small number of mitochondria and high ATPase activity.

Question 20

The change in muscle fiber type that would most likely occur as a result of endurance training is

A) type I $\rightarrow$ type II
B) type IIx $\rightarrow$ type IIa
C) type IIa $\rightarrow$ type IIx
D) type IIx $\rightarrow$ type I

Question 21

Rigor mortis is caused by an inability of myosin to enter a weak binding state with actin.

Question 22

In contrast to power athletes, endurance athletes typically possess a low percentage of slow fibers and a high percentage of fast fibers.

Question 23

At any given velocity of movement, the peak force is greater in muscles that contain a high percentage of fast-twitch fibers when compared to muscles that possess predominantly slow-twitch fibers.

Question 24

Tetanus is defined as the use of sufficient motor units to initiate movements.

Question 25

If you continue to increase the firing rate (of action potentials) of a motor neuron, then all of the skeletal muscle fibers it innervates will eventually summate to tetanus.

Question 26

Muscle atrophy may be caused by a decrease in protein production, as well as an increase in protein degradation.

Question 27

High activity of the enzyme ATPase is found in both slow-twitch and fast-twitch fibers.

Question 28

Recent evidence suggests that rigorous exercise training can result in a conversion of muscle fiber type.