Deck 8: A--Muscle Physiology

Question 1

Skeletal muscle fibers

A) have T tubules within their sarcomeres
B) have Z lines extending down the middle of the I bands
C) contain gap junctions
D) all of these
E) have T tubules within their sarcomeres, and Z lines extending down the middle of the I bands

Answer 1

B

Question 2

Actin

A) does not perform a power stroke during muscle contraction
B) contains a globular head that forms the cross bridges between the thick and thin filaments
C) is not found within A bands
D) is inhibited by Ca²⁺
E) none of these

Answer 2

A

Question 3

Myosin

A) is found in the A band
B) is found in the I band
C) is in the thin filaments
D) contracts during muscle contraction because it is one of the contractile proteins
E) none of these

Answer 3

A

Question 4

Cross bridges

A) bind to actin during muscle contraction
B) consist of tropomyosin heads
C) are globular heads made of myosin
D) do not bend during muscle contraction
E) bind to actin during muscle contraction and are globular heads made of myosin

Question 5

Troponin

A) binds with calcium to allow sarcomere shortening
B) breaks down myosin cross bridges
C) is an enzyme in the sarcomere
D) forms the boundaries of a sarcomere
E) all of these, except forms the boundaries of a sarcomere

Question 6

Skeletal muscle fibers

A) are some of the longest cells in the body
B) are attached end-to-end within a muscle
C) contain Z lines within their A bands
D) contain only one nucleus
E) all of these, except contain only one nucleus

Question 7

Actin

A) has ATPase activity
B) is spherical
C) forms a helical chain that forms the main structural component of the thin filaments
D) is spherical and forms a helical chain that forms the main structural component of the thin filaments
E) all of these

Question 8

Sarcomeres are arranged end to end as

A) fascicles
B) myofibrils
C) bands
D) perimysia
E) none of these

Question 9

A function of tropomyosin is to

A) bind Ca²⁺
B) form attachments with myosin cross bridges
C) prevent myosin cross bridges from attaching to the thin filaments
D) act as an ATPase
E) none of these

Question 10

The region between two Z lines is a

A) muscle fiber
B) myofibril
C) myofilament
D) sarcomere
E) sarcoplasmic reticulum

Question 11

The functional unit of skeletal muscle is the

A) smallest contractile component of a muscle fiber
B) area between two Z lines
C) sarcomere
D) area between two Z lines and sarcomere
E) all of these

Question 12

Thick filaments in skeletal muscle are composed of

A) actin
B) troponin and tropomyosin
C) myosin
D) actin, troponin, and tropomyosin
E) all of these

Question 13

The I band of the sarcomere is characterized by

A) overlapping thin and thick filaments
B) only the presence of thick filaments
C) the presence of thin filaments and actin
D) a dark coloration
E) the presence of thin filaments, actin, and a dark coloration

Question 14

Identify the characteristic(s) shared by all types of muscle tissues?

A) Every type is neurogenic.
B) Every type has T tubules.
C) Every type has tropomyosin.
D) All of these.
E) Every type has T tubules and tropomyosin.

Question 15

Z lines

A) are formed by the T tubules
B) extend down the middle of the I band
C) are formed by the cross bridges
D) are the thin filaments
E) extend down the middle of the sarcomere

Question 16

The striated appearance of skeletal muscle is due to the

A) orderly arrangement of the T tubules
B) orderly arrangement of the lateral sacs of the sarcoplasmic reticulum
C) orderly arrangement of the thick and thin filaments into A and I bands
D) orderly arrangement of the motor units
E) presence of white and red muscle fibers within the muscle

Question 17

The smallest unit of contraction within a skeletal muscle is a

A) myofibril
B) muscle fiber
C) sarcomere
D) thin filament
E) thick filament

Question 18

Myosin is

A) spherical
B) attached to tropomyosin
C) a regulatory protein
D) all of these
E) none of these

Question 19

Order the following muscle cell components from larger to smaller

A) 3, 4, 1, 5, 2
B) 1, 2, 3, 5, 4
C) 5, 4 ,3 , 1, 2
D) 5, 2, 3, 4, 1
E) 3, 4, 5, 2, 1

Question 20

Muscle fibers develop tension by

A) contraction of sarcomeres
B) shortening
C) the pushing of myosin by actin
D) contraction of sarcomeres and shortening
E) none of these

Question 21

The H zone

A) is the area within the middle of the A band where the thin filaments do not reach
B) shortens or disappears during contraction
C) contains only thick filaments
D) is in the middle of the A band
E) all of these

Question 22

Of the steps in excitation-contraction below, which occurs before the others?

A) Exposed actin sites bind with myosin cross bridges.
B) Sodium channels open in the fiber's membrane.
C) Calcium is released from the sarcoplasmic reticulum.
D) Troponin binds calcium.
E) Attachment of ATP allows for cross bridge detachment.

Question 23

The T tubules

A) store Ca²⁺
B) provide a means of rapidly transmitting the action potential from the surface into the central portions of the muscle fiber
C) store ATP
D) run longitudinally between the myofibrils
E) have expanded lateral sacs

Question 24

Cross bridge interaction between actin and myosin in skeletal muscle is directly blocked by

A) acetylcholine
B) triads
C) Z lines
D) calcium
E) tropomyosin

Question 25

Which is not characteristic of cross bridges?

A) They are a component of thin filaments.
B) They are comprised of myosin.
C) They have an actin binding site.
D) They have an ATPase binding site.
E) They provide power stroking.

Question 26

During contraction, asynchronous cycling of crossbridges

A) prevents tetany
B) prevents thick filaments from slipping backwards
C) prevents thin filaments from slipping backwards
D) utilizes less ATP
E) none of these

Question 27

Which molecules are involved with regulation of cross bridge attachment activity?

A) calcium ions
B) troponin
C) myosin
D) calcium ions and troponin
E) all of these

Question 28

Which of the following changes in banding pattern occur during muscle relaxation?

A) Thin filaments stretch away from the Z lines.
B) I bands get wider.
C) H zones get narrower.
D) Thick filaments stretch and become longer.
E) I bands get wider and H zones get narrower.

Question 29

During muscle contraction, the

A) Z lines move farther away from the thick filaments.
B) A band becomes narrower.
C) H zone becomes narrower or disappears.
D) I band remains unchanged.
E) Both H zone becomes narrower or disappears, and I band remains unchanged.

Question 30

The sarcoplasmic reticulum stores ____ when a muscle is relaxed and releases it for binding to ____ during contraction.

A) calcium; troponin
B) calcium; tropomyosin
C) sodium; tropomyosin
D) potassium; tropomyosin
E) sodium; troponin

Question 31

The T tubules

A) store Ca²⁺
B) provide a means of rapidly transmitting ACh to the central portions of the muscle fiber
C) provide attachment sites for ACh
D) provide a means of rapidly transmitting ACh to the central portions of the muscle fiber and provide attachment sites for ACh
E) none of these

Question 32

During a cross-bridge cycle in skeletal muscle, the

A) Cross bridge is energized when it hydrolyzes ATP.
B) Myosin cross bridge must bind with an ATPase before the cross bridge will experience a power stroke.
C) Ca²⁺ causes the troponin-tropomyosin complex to move off the actin-binding sites on myosin.
D) ADP binds to the cross bridge at the end of the power stroke.
E) Cross bridge is energized when it hydrolyzes ATP, and myosin cross bridge must bind with an ATPase before the cross bridge will experience a power stroke.

Question 33

During contraction of skeletal muscle fibers, the

A) Contractile proteins contract.
B) Thin filaments slide inward toward the A band's center as a result of cycles of cross-bridge binding and bending.
C) Thick and thin filaments become tightly coiled, thus shortening the sarcomere.
D) I bands slide in between the A bands.
E) Lateral sacs of the sarcoplasmic reticulum shrink, pulling the Z lines closer together.

Question 34

Sequence the following events involved in muscle cell contraction:

A) 1, 2, 3, 4, 5
B) 2, 1, 3, 4, 5
C) 2, 4, 3, 1, 5
D) 3, 4, 5, 1, 2
E) 3, 5, 2, 1, 4

Question 35

Binding of ____ to myosin permits the cross-bridge to ____.

A) ATP; bind with actin
B) ATP; detach from actin
C) calcium; bind with actin
D) calcium; detach from actin
E) none of these

Question 36

Foot proteins

A) span the gap between a lateral sac of the sarcoplasmic reticulum and the adjacent T tubule
B) are believed to serve as Ca²⁺ channels
C) bind to and pull the thin filaments inward toward the A band's center during muscle contraction
D) span the gap between a lateral sac of the sarcoplasmic reticulum and the adjacent T tubule, and are believed to serve as Ca²⁺ channels
E) none of these

Question 37

An action potential rapidly spreads to the central portions of a muscle cell by means of the

A) Z lines
B) sarcoplasmic reticulum
C) H zone
D) pores in the membrane surface
E) T tubules

Question 38

Which statement is incorrect about cross bridges?

A) They are globular myosin heads that protrude from the thick filaments.
B) They bend during muscle contraction.
C) They detach from actin during muscle contraction.
D) They are not found in the I band.
E) They bind with troponin during contraction.

Question 39

During excitation-contraction coupling,

A) The action potential travels down the T tubules.
B) Ca²⁺ is released from the sarcoplasmic reticulum.
C) Ca²⁺ is taken up by the sarcoplasmic reticulum.
D) The action potential travels down the T tubules, and Ca²⁺ is released from the sarcoplasmic reticulum.
E) The action potential travels down the T tubules, and Ca²⁺ is taken up by the sarcoplasmic reticulum.

Question 40

According to the sliding-filament mechanism, the

A) A bands slide in closer between the I bands.
B) Thin filaments slide inward toward the center of the A band.
C) Z lines slide in between the T tubules.
D) Contractile proteins contract, thus shortening the sarcomere.
E) Filaments slide into the lateral sacs of the sarcoplasmic reticulum.

Question 41

During an isometric contraction, the muscle

A) maintains a constant tension
B) shortens
C) moves a body part
D) maintains a constant length
E) tension is greater than the load

Question 42

To pick up something heavier than your pencil, your nervous system could

A) stimulate larger motor units
B) decrease the frequency of stimulation to allow a more prolonged contraction to occur
C) decrease the refractory periods
D) block acetylcholinesterase at the neuromuscular junction to allow acetylcholine to function longer
E) none of these

Question 43

With eccentric muscle contractions:

A) Development of tension occurs at constant muscle length.
B) Muscle lengthens while contracting.
C) Muscle shortens while contracting.
D) Muscle length and tension vary throughout a range of motion.
E) None of these.

Question 44

Muscles developing tension while lengthening are performing ____ contractions.

A) concentric
B) eccentric
C) isometric
D) fatiguing
E) oscillating

Question 45

Twitch summation

A) results from increases in cytosolic calcium levels
B) pumping of calcium into the sarcoplasmic reticulum
C) can be enhanced by allowing a cell to completely relax
D) rarely results in tetany
E) none of these

Question 46

Muscle tension

A) is created during muscle contraction as the tension generated by the contractile elements is transmitted via the connective tissue and tendons to the bones
B) is the force exerted on a muscle by the weight of an object
C) is greater than the load during an isometric contraction
D) all of these
E) none of these

Question 47

Based on the length-tension relationship,

A) Stretching a skeletal muscle 30% longer than the l_o results in a greater contraction.
B) Varying the amount of overlap of thick and thin filaments does not greatly affect contraction force as long as tension remains the same.
C) More tension develops if a muscle is 30%shorter than its resting length.
D) Muscle tension remains the same as long as the muscle's length is not more than $\pm$ 30% of the resting length.
E) A resting muscle that is shorter or longer than its l_o will generate less tension at the onset of contraction.

Question 48

Twitch summation

A) is a means by which gradation of muscle contraction may be accomplished
B) results from the additional release of Ca²⁺ within the cytosol of muscle fibers
C) results from increasing the frequency at which motor units are firing within a muscle
D) is a means by which gradation of muscle contraction may be accomplished and results from increasing the frequency at which motor units are firing within a muscle
E) all of these

Question 49

Which of the following is involved in muscle relaxation?

A) Acetylcholinesterase destroys acetylcholine to allow the muscle membrane to return to resting potential.
B) Ca²⁺ is actively taken up by the lateral sacs of the sarcoplasmic reticulum when there is no longer a local action potential.
C) The cross bridges pull the filaments back to their original resting positions.
D) Acetylcholinesterase destroys acetylcholine to allow the muscle membrane to return to resting potential, and Ca²⁺ is actively taken up by the lateral sacs of the sarcoplasmic reticulum when there is no longer a local action potential.
E) All of these.

Question 50

In a muscle fiber undergoing maximal tetanic stimulation, the velocity of shortening ____ as the load ____.

A) decreases; decreases
B) decreases; increases
C) increases; increases
D) remains constant; increases
E) remains constant; decreases

Question 51

Picking up a book at a constant speed requires that

A) muscle tension be equal to the book's weight
B) the muscle perform an eccentric contraction
C) the muscle perform an isometric contraction
D) the muscle perform a concentric contraction
E) muscle tension be equal to the book's weight and the muscle to perform a concentric contraction

Question 52

The origin of a muscle is its

A) main, thickest part
B) middle, thinner part
C) movable end of attachment
D) source of development in the fetus
E) stationary end of attachment

Question 53

In twitch summation:

A) The muscle fiber is stimulated again before the action potential has returned to resting potential.
B) The muscle fiber is stimulated again before the filaments have completely returned to their resting position.
C) Stronger muscle contractions occur but stronger action potentials do not occur.
D) The muscle fiber is stimulated again before the action potential has returned to resting potential, and stronger muscle contractions occur but stronger action potentials do not occur.
E) The muscle fiber is stimulated again before the filaments have completely returned to their resting position, and stronger muscle contractions occur but stronger action potentials do not occur.

Question 54

A motor unit refers to

A) a single motor neuron plus all of the muscle fibers it innervates
B) a single muscle fiber plus all of the motor neurons that innervate it
C) all of the motor neurons supplying a single muscle
D) a pair of antagonistic muscles
E) a sheet of smooth muscle cells connected by gap junctions

Question 55

Whole muscle tension depends on all of the following except

A) number of muscle fibers contracting
B) tension produced by each contracting fiber
C) extent of motor-unit recruitment
D) frequency of stimulation
E) the proportion of each motor unit used at any given time

Question 56

During an isotonic contraction:

A) Filaments do not shorten in the muscle.
B) Movement does not occur inside the muscle.
C) The muscle does not change length.
D) The muscle's tension does not overcome a load.
E) The muscle's tension remains constant.

Question 57

Which of the following is not involved in the relaxation of muscle?

A) synthesis of ACh by acetylcholinesterase
B) initiation of action potentials
C) the troponin-tropomyosin complex slipping back into its blocking position
D) detachment of actin from tropomyosin
E) T tubules actively absorbing Ca²⁺

Question 58

Submaximal isometric contractions are important for

A) moving large objects
B) walking
C) maintaining posture
D) writing
E) walking and maintaining posture

Question 59

The energy for cross bridge cycling during muscle contraction is provided by:

A) acetylcholine
B) Ca²⁺
C) ATP
D) myosin
E) actin

Question 60

A lack of ATP in a skeletal muscle cell would most likely cause

A) tension to decrease
B) cross bridges to detach from actin
C) the sarcomeres to become longer
D) an increase in tension and an inability to relax
E) the sarcomeres to become longer, an increase in tension, and an inability to relax

Question 61

During aerobic exercise, the primary means for ATP production in muscle fibers involves

A) creatine phosphate
B) fermentation
C) oxidative phosphorylation
D) glycolysis
E) myoglobin

Question 62

Conscious initiation of muscle contraction is controlled by

A) the spinal cord
B) the brain stem
C) the cerebral cortex
D) the thalamus
E) none of these

Question 63

In the body's lever systems, the fulcrums are represented by the

A) joints
B) long bones
C) tendons
D) short bones
E) skeletal muscles

Question 64

The muscle cells of a marathon runner's legs would exhibit all these characteristics except

A) high resistance to fatigue
B) low myoglobin content
C) low glycogen content
D) many mitochondria
E) slow speed of contraction

Question 65

Which of the following does not directly influence motor neurons?

A) primary motor cortex
B) cerebellum
C) brain stem
D) afferent neurons (through intervening interneurons)
E) none of these

Question 66

Enlargement of muscle due to weight lifting is primarily a result of

A) hypertrophy
B) hyperplasia
C) increased production of actin and myosin
D) increases in the number of cells
E) hypertrophy and increased production of actin and myosin

Question 67

The corticospinal system

A) consists of fibers that originate within the primary motor cortex and terminate on motor neurons
B) involves the motor regions of the cortex, the cerebellum, the basal nuclei, and the thalamus
C) is primarily concerned with regulation of overall body posture
D) consists of fibers that originate within the primary motor cortex and terminate on motor neurons, and is primarily concerned with regulation of overall body posture
E) involves the motor regions of the cortex, the cerebellum, the basal nuclei, and the thalamus and is primarily concerned with regulation of overall body posture

Question 68

Which of the following statements about the different types of muscle fibers is incorrect?

A) The higher the ATPase activity, the faster the speed of contraction.
B) Muscles that have high glycolytic capacity and large glycogen stores are more resistant to fatigue.
C) Muscles with high ATP-synthesizing ability are more resistant to fatigue.
D) Oxidative types of muscle fibers contain myoglobin.
E) Muscle fibers containing large amounts of myoglobin have a dark red color in comparison to the paler fibers, which have little myoglobin.

Question 69

Select the correct statement about the summation of simple twitches.

A) They can occur because of the long duration of the action potential in a muscle fiber.
B) They reduce the tension in a muscle.
C) They result from the slow stimulation of a muscle fiber.
D) The effect is unrelated to the refractory periods of action potentials.
E) The twitches resulting from separate action potentials add together.

Question 70

Fast-oxidative (type IIa) fibers

A) contain very few mitochondria
B) can be converted into fast-glycolytic fibers by regular resistance activities
C) are most abundant in muscles specialized for maintaining low-intensity contractions for long periods of time without fatigue
D) can be converted into fast-glycolytic fibers by regular resistance activities and are most abundant in muscles specialized for maintaining low-intensity contractions for long periods of time without fatigue
E) all of these

Question 71

Which statement below is characteristic of most of the body's lever systems?

A) They work at mechanical advantage.
B) They work at a mechanical disadvantage.
C) Muscles must exert greater forces than the load.
D) They work at mechanical advantage and at a mechanical disadvantage.
E) They work at a mechanical disadvantage, and muscles must exert greater forces than the load.

Question 72

The first means by which ATP is produced at the onset of contractile activity is

A) transfer of energy and phosphate from creatine phosphate to ADP
B) oxidative phosphorylation
C) glycolysis
D) degradation of myoglobin
E) none of these

Question 73

With the type of lever system exemplified by flexion of the elbow joint, when an object is held in the hand, the

A) power arm of the lever is the distance between the elbow joint and the insertion of the biceps muscle
B) load arm of the lever is the distance between the elbow joint and the hand
C) velocity and distance moved by the hand is amplified at the expense of the biceps muscle having to exert considerably greater force than the actual load that is moved
D) only two of these
E) all of these

Question 74

Muscular fatigue can be caused by

A) lactic acid accumulation
B) depletion of ATP
C) depletion of ACh
D) all of these
E) lactic acid accumulation and depletion of ATP

Question 75

If the load on a muscle is increased, eventually a load will be reached at which the velocity of shortening becomes zero. At this point, the muscle contraction is referred to as

A) concentric
B) eccentric
C) isotonic
D) isokinetic
E) isometric

Question 76

Energy sources available to form ATP in muscle fibers in the absence of oxygen include

A) creatine phosphate
B) chemiosmosis
C) glycolysis
D) creatine phosphate and glycolysis
E) chemiosmosis and glycolysis

Question 77

Fatigue is the failure of a muscle fiber to maintain ____ as a result of previous contractile activity.

A) excitability
B) muscle mass
C) tension
D) sarcomere number
E) mitochondria

Question 78

Fast-glycolytic (type IIx) muscle fibers

A) have high myosin-ATPase activity
B) can carry out oxidative phosphorylation
C) fatigue rapidly
D) contain myoglobin
E) all of these

Question 79

Myoglobin

A) can store small amounts of O₂
B) increases the rate of O₂ transfer from the blood into muscle fibers
C) is abundant in fast-glycolytic fibers
D) can store small amounts of O₂ and increases the rate of O₂ transfer from the blood into muscle fibers
E) all of these

Question 80

When a muscle atrophies:

A) The muscle fibers split lengthwise.
B) It decreases in mass and becomes weaker.
C) Its fibers increase in diameter.
D) Its fibers undergo mitotic cell division.
E) The muscle fibers dissolve and are replaced by fibrous scar tissue.