Chapter 12: Muscle Physiology

Question 1

A skeletal muscle is composed of a number of ________, each composed of many muscle fibers bundled by connective tissue.

Answer 1

fascicles

Question 2

What structure composed of connective tissue transmits force from contracting skeletal muscle to bone?

Answer 2

tendon

Question 3

What is the saclike membranous network that surrounds each myofibril called?

Answer 3

sarcoplasmic reticulum

Question 4

The fundamental repeating unit of the myofibril called a ________ gives skeletal muscle its striated appearance, and is bordered by ________.

Answer 4

sarcomere : Z lines

Question 5

What is the region of the striated muscleʹs banding patterns that contains only the connections between the tails of myosin molecules?

Answer 5

M line

Question 6

The contractile portion of the thin filament is composed of what protein?

Answer 6

actin

Question 7

What is the protein component of the thin filament that binds to calcium thereby initiating skeletal muscle contraction?

Answer 7

troponin

Question 8

Which of the following is a structural protein that extends along each thick filament from M line to Z line.

Answer 8

Titin

Question 9

The shortening of a skeletal muscle fiber during contraction involves which of the following?

Answer 9

the sarcomeres shortening

Question 10

During skeletal muscle contraction, as the muscle shortens, the thick and thin filaments _______

Answer 10

slide past one another

Question 11

When a skeletal muscle is passively stretched, that cell has a tendency to spring back once the force that was stretching the muscle is removed due to ________.

Answer 11

titin acting as a spring using the energy stored by the stretching

Question 12

The repeated, oscillating interaction between actin and myosin that results in the generation of force by a skeletal muscle cell is called what?

Answer 12

crossbridge cycling

Question 13

What converts the myosin head into the high-energy state?

Answer 13

the hydrolysis of ATP

Question 14

The release of an inorganic phosphate from the myosin molecule directly results in which of the following?

Answer 14

power stroke

Question 15

In order for crossbridge cycling to occur, the actin-myosin complex must be broken by which of the following?

Answer 15

binding of ATP to myosin

Question 16

The sequence of events that links the action potential to changes in skeletal muscle force development is called what?

Answer 16

excitation-contraction coupling

Question 17

During skeletal muscle contraction, multiple crossbridge cycles are occurring between the same thick and thin filament. Which of the following best describes this process?

Answer 17

Crossbridge cycling is asynchronous between a certain thick and thin filament.

Question 18

Contraction of skeletal muscle fibers is stimulated by what type of neuron?

Answer 18

motor neurons

Question 19

Which of the following is NOT a specialization observed at the neuromuscular junction?

Answer 19

Each muscle fiber is innervated by multiple motor neurons.

Question 20

Increases in the amount of cytoplasmic calcium required to initiate a muscle contraction are mediated by the coupling between a ________ on the T tubule and a ________ on the membrane of the sarcoplasmic reticulum.

Answer 20

dihydropyridine receptor : ryanodine receptor

Question 21

Which of the following is the voltage sensor that initiates an increase in cytoplasmic calcium in response to an action potential?

Answer 21

dihydropyridine receptor

Question 22

The binding of calcium to troponin will directly cause which of the following?

Answer 22

the movement of tropomyosin, thereby exposing the myosin-binding site on the actin
molecule

Question 23

What portion of a sarcomere shows up as light striations when viewed under a microscope?

Answer 23

I band

Question 24

Which of the following best describes the function of transverse (t) tubules and the sarcoplasmic reticulum in skeletal muscle contraction?

Answer 24

Action potentials in T tubules are detected by DHP receptors, which are coupled to ryanodine receptors in the sarcoplasmic reticulum and open channels for calcium.

Question 25

During the cross-bridge cycle, ATP binding to myosin causes which of the following?

Answer 25

the myosin head to detach from actin

Question 26

What is the function of T tubules?

Answer 26

They conduct action potentials from the sarcolemma to the interior of the muscle cell.

Question 27

What is a motor unit?

Answer 27

a motor neuron and all the muscle fibers it innervates

Question 28

In order to allow discrete contractile events to occur, calcium is rapidly removed from the cytoplasm via ________.

Answer 28

calcium pumps (active transport of calcium)

Question 29

Which of the following is NOT part of the process whereby skeletal muscles relax?

Answer 29

Sarcolemmal calcium channels open to allow the efflux of calcium.

Question 30

What enzyme catalyzes the reaction that creates creatine phosphate?

Answer 30

creatine kinase

Question 31

Since the creatine phosphorylation reaction is substrate driven, an increase in the concentration of creatine within a skeletal muscle fiber will directly have what effect?

Answer 31

increase creatine phosphate concentration

Question 32

During intense (heavy) exercise, the ability of oxidative phosphorylation to provide enough ATP for force generation by the skeletal muscle is ________, thereby causing the muscle fiber to derive energy from ________.

Answer 32

diminished : substrate-level phosphorylation

Question 33

As the intensity of exercise increases, the muscles switch from oxidative to substrate-level phosphorylation, resulting in the increased generation of which of the following?

Answer 33

lactic acid

Question 34

When an action potential is generated within a motor neuron, ________.

Answer 34

every muscle cell of the motor unit is stimulated to contract

Question 35

Which is the longest phase of a twitch?

Answer 35

relaxation

Question 36

Which of the following is NOT part of the explanation for the all-or-nothing property of an isometric twitch contraction of skeletal muscle?

Answer 36

equivalent activation of calmodulin stimulating myosin light-chain kinase activity

Question 37

Which of the following is a property of isometric skeletal muscle contraction?

Answer 37

load is greater than the force generated by the muscle

Question 38

Which of the following is a property of isotonic skeletal muscle contraction?

Answer 38

load is less than the force generated by the muscle

Question 39

Which of the following statements about excitation-contraction coupling in skeletal muscle is FALSE?

Answer 39

An action potential in the sarcolemma stimulates the opening of voltage-gated calcium channels in the plasma membrane and the sarcoplasmic reticulum.

Question 40

Which of the following statements about end-plate potentials is FALSE?

Answer 40

They are a result of acetylcholine binding to muscarinic cholinergic receptors.

Question 41

Which of the following best describes an isotonic contraction?

Answer 41

When the contractile elements shorten, they create enough force to move the load.

Question 42

The speed with which the skeletal muscle generates force is determined primarily by _______

Answer 42

the type of myosin present

Question 43

Which of the following is the property of skeletal muscle whereby an increase in the frequency of action potentials enhances the force developed by the muscle cell?

Answer 43

Summation

Question 44

The tension produced during skeletal muscle contraction can be increased by all of the following except one. Which one is it?

Answer 44

increasing the load on the muscle

Question 45

Which of the following statements about summation and tetanus is FALSE?

Answer 45

The maximum tension developed during summation and tetanus is treppe.

Question 46

Once a skeletal muscle cell begins to shorten during an isotonic twitch contraction, ________.

Answer 46

the amount of force generated by the muscle will remain constant

Question 47

Which of the following conditions will result in a skeletal muscle that produces a greater amount of force?

Answer 47

more sarcomeres in parallel

Question 48

Which of the following is NOT an accurate description of specific muscle fiber types?

Answer 48

Slow oxidative fibers are quick to fatigue.

Question 49

As skeletal muscle is further stretched beyond the length where optimum force is developed, ______

Answer 49

the thin filaments are pulled away from one another, thereby reducing their ability to interact with myosin

Question 50

As the sarcomere length of skeletal muscle is reduced beyond the length where optimum force is developed, ______

Answer 50

the thin filaments overlap one another, thereby reducing their ability to interact with myosin

Question 51

In the body, the sarcomere length of skeletal muscle cells is usually ________.

Answer 51

near optimal

Question 52

Which of the following does NOT influence the force generated by an individual muscle fiber?

Answer 52

recruitment

Question 53

What is an increase in the number of active motor units that would increase the force developed by a skeletal muscle called?

Answer 53

Recruitment

Question 54

Contraction of motor units in a(n) ________ manner allows a muscle to maintain a level of force for a duration of time without fatiguing.

Answer 54

asynchronous

Question 55

Which of the following best describes the relationship between motor neuron size, motor unit size, and order of recruitment?

Answer 55

large motor neurons : large motor unit : last to be recruited

Question 56

A muscle is stimulated at a frequency that allows the muscle to relax completely between contractions. However, the amount of tension increases with each contraction. What is this called?

Answer 56

treppe

Question 57

The mechanism responsible for the size principle involves ________.

Answer 57

smaller motor neurons that contain the least number of muscle cells and reach threshold easier than larger neurons

Question 58

Which of the following is NOT a property of glycolytic fibers as compared to oxidative fibers?

Answer 58

poor ability to produce ATP in the absence of oxygen

Question 59

What molecule present primarily within oxidative skeletal muscle cells acts as an oxygen buffer due to its ability to bind oxygen?

Answer 59

Myoglobin

Question 60

What causes some muscle fibers to appear red?

Answer 60

presence of myoglobin

Question 61

What is the site where a muscle attaches to a stationary bone called?

Answer 61

origin

Question 62

What connects muscles to bone?

Answer 62

tendons

Question 63

Relative to the triceps muscle, the biceps is its ________.

Answer 63

antagonist

Question 64

What type of receptor detects muscle length?

Answer 64

muscle spindle

Question 65

What is an annulospiral ending?

Answer 65

sensory endings in the muscle spindle that detect muscle length

Question 66

What type of efferent neuron innervates intrafusal muscle fibers?

Answer 66

gamma motor neurons

Question 67

Which of the following statements is TRUE regarding activation of alpha and gamma motor neurons?

Answer 67

Alpha and gamma motor neurons are activated at the same time.

Question 68

Which of the following is the correct order of muscle fiber recruitment from first to last?

Answer 68

slow oxidative : fast oxidative : fast glycolytic

Question 69

Which of the following muscle types has the slowest contraction time?

Answer 69

smooth muscle

Question 70

Which of the mechanisms listed below does NOT account for the decrease in force development by muscle cells during sustained force development?

Answer 70

The crossbridges can become resistant to ATP.

Question 71

Which of the following is NOT an adaptation of skeletal muscle that would be observed in response to aerobic training?

Answer 71

an increase in the diameter of the skeletal muscle fibers

Question 72

Where are gap junctions commonly found?

Answer 72

both single-unit smooth muscle and cardiac muscle

Question 73

Which of the following is true of ALL muscle types?

Answer 73

contract by using the sliding filament mechanism and cross-bridge cycling

Question 74

In smooth muscle, calcium triggers contraction by binding to what protein?

Answer 74

calmodulin

Question 75

Calcium binding to calmodulin causes phosphorylation of what protein in what type of muscle?

Answer 75

myosin in smooth muscle only

Question 76

Which of the following adaptations does NOT generally occur with aerobic exercise?

Answer 76

an increase in the number of myofibrils per muscle fiber

Question 77

The interaction between actin and myosin in smooth muscle requires ________.

Answer 77

that the calcium-calmodulin complex activates myosin light-chain kinase, which phosphorylates myosin light chain thereby allowing myosin to bind with actin

Question 78

What is the source of variability in the response of smooth muscle cells from different organs to autonomic nervous activity (some relax to sympathetic nervous output while others contract)?

Answer 78

the type of receptor present on the effector organ

Question 79

Which of the following could cause a pacemaker potential?

Answer 79

spontaneous opening of sodium channels

Question 80

The continuation of the sarcolemma that penetrates the interior of the muscle fiber and thereby facilitates the release of calcium from the sarcoplasmic reticulum is called what?

Answer 80

transverse tubule

Question 81

What is the protein component of the thin filament that blocks the myosin-binding site on the actin monomer?

Answer 81

tropomyosin

Question 82

Troponin is a complex of three proteins that bind to ________, ________, and ________.

Answer 82

tropomyosin, calcium, and actin

Question 83

Calcium is stored in what region of skeletal muscle cells?

Answer 83

sarcoplasmic reticulum

Question 84

Another name for a muscle cell is (myofibril / muscle fiber).

Answer 84

muscle fiber

Question 85

Name the three proteins found in thin filaments.

Answer 85

actin, troponin, and tropomyosin

Question 86

Following death, rigor mortis occurs due to a lack of (calcium / ATP).

Answer 86

ATP

Question 87

Receptor types at the motor end plate are (muscarinic / nicotinic) cholinergic receptors.

Answer 87

nicotinic

Question 88

(Dihyropyridine / Ryanodine) receptors are located on the sarcoplasmic reticulum.

Answer 88

ryanodine

Question 89

Heavy intensity exercise generates what by-product that contributes to fatigue?

Answer 89

lactic acid

Question 90

During summation, calcium release is (greater than / less than / equal to) calcium reuptake.

Answer 90

greater than

Question 91

The time between the occurrence of an action potential in skeletal muscle and the onset of tension is called what?

Answer 91

latent period

Question 92

List the three mechanisms whereby force of individual skeletal muscle fibers can be altered.

Answer 92

frequency of stimulation (summation), fiber diameter (sarcomeres in parallel), and fiber length

Question 93

The velocity at which a skeletal muscle contracts is (directly / inversely) related to load.

Answer 93

inversely

Question 94

Name the two types of sensory endings found in muscle spindles.

Answer 94

annulospiral endings, flower-spray endings

Question 95

What type of motor neuron innervates intrafusal muscle fibers?

Answer 95

gamma

Question 96

Name the antagonistic muscle to the triceps.

Answer 96

biceps

Question 97

Identify the three types of muscle fibers that are found in all skeletal muscles.

Answer 97

slow oxidative, fast oxidative, and fast glycolytic

Question 98

Postural muscles of the legs and back tend to have a high proportion of this fiber type.

Answer 98

slow oxidative

Question 99

In smooth muscle, calcium binds to ________, and then activates the enzyme ________.

Answer 99

calmodulin : myosin light-chain kinase

Question 100

The decreased ability of a muscle to maintain a constant force of contraction during repetitive stimulation is called what?

Answer 100

fatigue

Question 101

In smooth muscle, the structures analogous to Z lines in skeletal muscle are called ________.

Answer 101

dense bodies

Question 102

(Single-unit / Multi-unit) smooth muscle contains pacemaker cells.

Answer 102

Single-unit

Question 103

Cardiac muscle is (smooth / striated).

Answer 103

striated

Question 104

Intercalated disks contain what type of special junctions?

Answer 104

gap junctions and tight junctions