Deck 6: Muscle Physiology

Question 1

Muscle fibres are some of the longest cells in the body.How long can they be?

A) 1 to 2 micrometres
B) 2 to 4 micrometres
C) 10 to 100 micrometres
D) 500 to 1,000 micrometres

Answer 1

C

Question 2

What composes thick filaments in skeletal muscle?

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

Answer 2

C

Question 3

Which statement concerning cross bridges is INCORRECT?

A) Cross bridges bind to actin during muscle contraction.
B) Cross bridges are formed by the globular heads of the myosin molecules.
C) Cross bridges consist of troponin and tropomyosin protruding from the actin helix.
D) Cross bridges bend during muscle contraction.

Answer 3

C

Question 4

What is the functional unit of skeletal muscle?

A) largest contractile component of a muscle fibre
B) area between two Z lines
C) sarcoplasmic reticulum
D) area between two I bands

Question 5

How are Sarcomeres arranged end to end?

A) as fascicles
B) as myofibrils
C) as bands
D) as perimysia

Question 6

What are in the I band of the sarcomere?

A) overlapping thin and thick filaments
B) only thick filaments
C) only thin filaments
D) 2 Z lines

Question 7

Which statement concerning myosin is correct?

A) It is found in the A band.
B) It is found in the I band.
C) It is the primary protein found in the thin filaments.
D) It contracts during muscle contraction because it is one of the contractile proteins.

Question 8

Which statement is correct for Actin?

A) It has ATPase activity.
B) It is shaped like a golf club.
C) It forms a helical chain that forms the main structural component of the thin filaments.
D) It is a regulatory protein.

Question 9

Which statement concerning Z lines is correct?

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

Question 10

What is involved in developing muscle fibres tension?

A) contraction of sarcomeres
B) lengthening of sarcomeres
C) the pushing of myosin by actin
D) elongation of myosin fibres

Question 11

What is the function of tropomyosin?

A) to bind Ca2+
B) to form attachments with myosin cross bridges
C) to prevent myosin cross bridges from attaching to the thin filaments
D) to serve as an ATPase

Question 12

Rank muscle cell components from largest to smallest.
1)troponin
2)myofibril
3)sarcomere
4)thin filament
5)muscle fibre

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

Question 13

What is the term for the region between two Z lines?

A) muscle fibre
B) myofibril
C) myofilament
D) sarcomere

Question 14

What is the striated appearance of skeletal muscle due to?

A) regular orderly arrangement of the T tubules
B) regular orderly arrangement of the lateral sacs of the sarcoplasmic reticulum
C) regular orderly arrangement of the thick and thin filaments into A and I bands
D) regular orderly arrangement of the motor units

Question 15

Which statement is correct for Actin?

A) It is spherical.
B) It contains a globular head that forms the cross bridges between the thick and thin filaments.
C) It is referred to as a regulatory protein.
D) It is inhibited by Ca2+.

Question 16

What is the smallest unit of contraction within a skeletal muscle?

A) myofibril
B) muscle fibre
C) sarcomere
D) thin filament

Question 17

Which statement is correct for troponin?

A) It binds with calcium in skeletal muscle contraction
B) It breaks down actin.
C) It breaks down myosin.
D) It forms the boundaries of a sarcomere.

Question 18

What causes the striated appearance of skeletal muscle?

A) regular arrangement of the T tubules running transversely through the muscle fibre
B) presence of the Z lines extending down the middle of the I bands
C) presence of gap junctions
D) regular arrangement of highly organized thick and thin filaments

Question 19

Which characteristics are shared by all three types of muscle tissues?

A) All contain myosin and actin.
B) All are neurogenic.
C) All are striated.
D) All are considered to be under voluntary control.

Question 20

Which statement concerning myosin is correct?

A) It is spherical in shape.
B) It is the main structural component of the thin filaments.
C) It is referred to as a contractile protein.
D) It consists of four identical protein subunits.

Question 21

Which statement concerning the H zone is correct?

A) It is the area within the middle of the Z lines where the thin filaments do not reach.
B) It shortens or disappears during contraction.
C) It contains only thin filaments.
D) It is the area within the middle of the I band.

Question 22

Which of the following events happens during excitation-contraction coupling?

A) The action potential travels down the thin myofilaments
B) Ca2+ is released from the sarcoplasmic reticulum.
C) Ca2+ is taken up by the sarcoplasmic reticulum.
D) Calcium blocks the binding sites on the actin molecules.

Question 23

What happens during muscle contraction?

A) The contractile proteins contract.
B) The A band becomes shorter.
C) The H zone becomes smaller or disappears.
D) The I band remains unchanged.

Question 24

What happens during contraction of skeletal muscle fibres?

A) Contractile proteins contract.
B) Thin filaments slide inward toward the A band's centre 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.

Question 25

Which statement is correct for the T tubules?

A) They form the Z lines.
B) They store Ca2+.
C) They provide a means of rapidly transmitting the action potential to the central portions of the muscle fibre.
D) They allow for nutrients to be carried into the cell.

Question 26

Which statement concerning cross bridges is correct?

A) They extend between the A and I bands and bend to pull the bands together during muscle contraction.
B) They are formed by the spherical actin molecules.
C) They extend from the thick filaments and bind to actin, then bend to pull the thin filaments in closer together during muscle contraction.
D) The A band is shorter.

Question 27

What happens during a cross-bridge cycle in skeletal muscle?

A) The cross bridge is energized as myosin ATPase activity hydrolyzes ATP.
B) The myosin cross bridge is able to bind with troponin molecule when Ca2+ pulls the troponin-tropomyosin complex aside.
C) The linkage between actin and the myosin cross bridge is broken at the end of the cross-bridge cycle as Mg2+ binds to the cross bridge.
D) The power strokes of all cross bridges are directed toward the periphery of the thick filament.

Question 28

Which statement is NOT characteristic of cross bridges?

A) They are a component of thin filaments.
B) They are composed of myosin.
C) They have an actin binding site.
D) They have an ATPase binding site.

Question 29

The sarcoplasmic reticulum stores which substance when a muscle is relaxed and releases it for binding to which substance during contraction?

A) It stores calcium for binding to troponin.
B) It stores calcium when binding to tropomyosin
C) It stores sodium when binding to tropomyosin
D) It stores potassium when binding to tropomyosin

Question 30

Binding of which substance to myosin permits cross bridge of which action between actin and myosin?

A) Binding ATP will bind actin and myosin.
B) Binding ATP will detach actin and myosin
C) Binding calcium will bind actin and myosin.
D) Binding calcium will detach actin and myosin.

Question 31

How does an action potential rapidly spread to the central portions of a muscle cell?

A) by means of the Z lines
B) by means of the sarcoplasmic reticulum
C) by means of the H zone
D) by means of the T tubules

Question 32

Which of the following is the first step in excitation-contraction coupling?

A) Exposed actin sites bind with myosin cross bridges.
B) Sodium channels open in the fibre's membrane.
C) Calcium is released from the sarcoplasmic reticulum.
D) Troponin binds calcium.

Question 33

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

Question 34

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

A) calcium ions and troponin
B) troponin and titin
C) tropomyosin and calmodulin
D) titin only

Question 35

Which statement concerning foot proteins is correct?

A) They span the gap between a lateral sac of the sarcoplasmic reticulum and the cell membrane.
B) They are believed to serve as Ca2+ channels.
C) They project from the thick filaments, bind to the thin filaments, and subsequently bend to pull the thin filaments inward toward the A band's centre during muscle contraction.
D) Each foot protein contains two subunits arranged in a specific pattern.

Question 36

Which statement concerning cross bridges is INCORRECT?

A) They are formed by the globular heads of the myosin molecules as they protrude from the thick filaments.
B) They bind to actin during muscle contraction.
C) They are not found in the I band.
D) They bind with troponin and tropomyosin during muscle contraction to pull them away from the actin helical chain.

Question 37

Which events involved in muscle cell contraction are sequenced in the correct order?
1)Sodium channels open,allowing sodium to flow in.
2)Impulse reaches axon's synaptic knob.
3)ACh binds to receptors on sarcolemma.
4)Synaptic vesicles fuse with neuron's membrane and release ACh via exocytosis.
5)If enough sodium moves into the muscle cell,an impulse (action potential)develops.

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

Question 38

Which statement concerning the T tubules is correct?

A) They store Ca2+.
B) They provide a means of rapidly transmitting the action potential from the surface into the central portions of the muscle fibre.
C) They store ATP.
D) They run longitudinally between the myofibrils.

Question 39

Which statement is true regarding the sliding-filament mechanism of muscle contraction?

A) A bands slide in closer between the I bands
B) thin filaments slide inward toward the centre of the A band
C) Z lines slide in between the T tubules
D) contractile proteins contract, thus shortening the sarcomere

Question 40

Which statement concerning cross bridges is INCORRECT?

A) Cross bridges are the globular heads of myosin molecules.
B) Cross bridges have actin binding sites that are normally covered by troponin and tropomyosin except during excitation-contraction coupling.
C) Cross bridges bind with actin and then bend to pull the thin filaments inward during contraction according to the sliding filament mechanism.
D) Mg2+ is necessary to bind ATP to the cross bridge.

Question 41

If you wanted to pick up something heavier than your pencil,you would need to have a stronger muscle contraction.In what way might you accomplish this?

A) Stimulate more motor units.
B) Decrease the frequency of stimulation to allow a more prolonged contraction to occur.
C) Decrease the refractory period.
D) Block acetylcholinesterase at the neuromuscular junction to allow acetylcholine to function longer.

Question 42

What would happen if ATP supplies became very low or not available in a muscle cell?

A) an increase in tension development
B) cross bridges detach from actin
C) muscles relax
D) ATP is not required for detachment from actin

Question 43

What directly blocks cross bridge interaction between actin and myosin in skeletal muscle?

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

Question 44

Which statement concerning the length-tension relationship of skeletal muscle is INCORRECT?

A) When a muscle is maximally stretched, it can develop the most tension upon contraction because the thin filaments can slide a maximal distance.
B) Maximum tension can be developed if the muscle is at its lowest at the onset of contraction.
C) In the body, the relaxed length of muscle is at its optimal length.
D) When the initial length of muscle prior to contraction becomes very short, tension is decreased during contraction because of thin filament overlap, because the thick filaments are compressed against the Z lines, and because not as much Ca2+ is released during excitation-contraction coupling.

Question 45

Which statement concerning the length-tension relationship is INCORRECT?

A) It refers to the relationship between the length of the muscle before the onset of contraction and the tetanic tension that each contracting fibre can subsequently develop at that length.
B) It is based on the amount of overlap of thick and thin filaments.
C) It allows no tension development if the whole muscle is stretched to 30 percent longer than its optimal length.
D) Within the body, it is limited to a functional range because of limitations on muscle length imposed by attachment to the skeleton.

Question 46

What causes muscle relaxation?

A) addition of magnesium to muscle cells
B) ACh hyperactivity
C) return of calcium to lateral sacs
D) lack of ATP

Question 47

Why are you able to repeatedly contract and relax your muscles of respiration,allowing you to breathe in and breathe out?

A) As soon as all of the Ca2+ stored in the lateral sacs of the sarcoplasmic reticulum is used up, muscle relaxation occurs.
B) After the muscle cell becomes excited, acetylcholinesterase maintains the action of acetylcholine.
C) When there is no longer a local action potential in the muscle cell, Ca2+ is actively transported back into the lateral sacs of the sarcoplasmic reticulum, and muscle relaxation occurs.
D) because ATP is not available soon after the contraction.

Question 48

Which statement concerning in twitch summation is correct?

A) The muscle fibre is stimulated again before the action potential has returned to resting potential.
B) The muscle fibre is stimulated again before the filaments have completely returned to their resting position.
C) Stronger muscle contractions occur with stronger action potentials.
D) Weaker muscle contractions in spite of stronger action potentials.

Question 49

What provides the energy for cross-bridge cycling during muscle contraction?

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

Question 50

To pick up a book which statement is true?

A) muscle tension must be lesser than the load
B) the muscle must lengthen during contraction
C) muscle tension remains constant as the muscle changes length
D) muscle length remains constant as the muscle tension changes

Question 51

Which of the following is NOT a determinant of whole muscle tension?

A) the number of muscle fibres contracting
B) the tension produced by each contracting fibre
C) the extent of motor-unit recruitment
D) the proportion of each motor unit that is contracting at any given time

Question 52

Which statement is correct for a motor unit?

A) a single motor neuron plus all of the muscle fibres it innervates
B) a single muscle fibre plus all of the motor neurons that innervate i.
C) all of the motor neurons supplying a single muscle
D) a pair of antagonistic muscles

Question 53

Which statement is correct for muscle tension?

A) It 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) It is the force exerted on a muscle by the weight of an object.
C) It is greater than the load during an isometric contraction.
D) It is lesser than the load during isometric contraction

Question 54

What is involved in the process of muscle relaxation?

A) Acetylcholinesterase promotes the concentration of 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 from the thick filaments bind to the thin filaments and bend in such a way as to return the filaments to their original resting position.
D) ATP is no longer available.

Question 55

Where does a muscle originate?

A) main, thick part of the structure
B) middle, thin part of the structure
C) movable end of attachment
D) stationary end of attachment

Question 56

What is involved in the gradation of muscle contraction?

A) greater number of muscle fibres
B) variation in the frequency of action potentials initiated in each muscle fibre
C) variation in the size of the action potentials initiated in each muscle fibre
D) variation in the distance action potentials can travel

Question 57

Which statement is correct for twitch summation?

A) It is a means by which weak muscle contraction may be accomplished.
B) It results from increasing the number of motor units that are firing within a muscle.
C) It results from increasing the frequency at which motor units are firing within a muscle.
D) A high level of calcium ion is not required in twitch summation.

Question 58

Which statement concerning summation is correct?

A) It results from increases in cytosolic calcium levels.
B) pumping of calcium into the sarcoplasmic reticulum.
C) It can be enhanced by allowing a cell to completely relax.
D) It rarely results in tetany.

Question 59

What is NOT a method of gradation of skeletal muscle contraction?

A) twitch summation
B) motor unit recruitment
C) stimulating variable portions of each motor unit
D) varying the number of motor units stimulated

Question 60

What is NOT involved in the relaxation of muscle?

A) when acetylcholine is destroyed by acetylcholinesterase
B) when there is no longer a local action potential
C) when the T tubules actively take up the Ca2+ was released
D) when the actin and myosin molecules are no longer bound together

Question 61

Which characteristics would NOT be exhibited in the muscle cells of a marathon runner's legs?

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

Question 62

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,what is the term for the muscle contraction?

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

Question 63

Which statement 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 lesser forces than the load.
D) Extension of the elbow joint is the most common type of lever system.

Question 64

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

A) joints
B) long bones
C) tendons
D) short bones

Question 65

During an isotonic contraction of a muscle in the arm which of the following occurs?

A) the muscle movement does not occur.
B) the muscle does not change length.
C) the tension in the muscle does not overcome a load.
D) the tension in the muscle remains constant.

Question 66

Which of the following properties characterize fast-oxidative (type IIa)muscle fibres?

A) high myosin-ATPase activity
B) low myosin-ATPase activity
C) low oxidative capacity
D) high oxidative capacity.

Question 67

With eccentric muscle contractions which statement is true?

A) the development of tension occurs at constant muscle length.
B) the muscle lengthens while contracting.
C) the muscle shortens while contracting.
D) muscle length and tension vary throughout a range of motion.

Question 68

Which statement concerning the characteristics of different types of muscle fibres 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 fibres contain myoglobin.

Question 69

During aerobic exercise,what is the primary means by which ATP is produced for contractile activity?

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

Question 70

What does NOT directly influence motor neurons?

A) primary motor cortex
B) cerebellum
C) brain stem
D) afferent neurons (through intervening interneurons)

Question 71

Muscles developing tension while lengthening,are performing on what type of contractions?

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

Question 72

Which statement is correct about the summation of simple twitches?

A) They can occur from the long duration of the action potential in a muscle fibre.
B) They reduce the tension in a muscle.
C) They result from the slow stimulation of a muscle fibre.
D) The twitches from action potentials add together.

Question 73

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

A) transfer of energy and phosphate from creatine phosphate to ADP
B) oxidative phosphorylation
C) glycolysis
D) degradation of myoglobin

Question 74

Which statement concerning myoglobin is correct?

A) It can store small amounts of CO2.
B) It increases the rate of O2 transfer from the blood into muscle fibres.
C) It is abundant in fast-glycolytic fibres.
D) It is abundant in slow red fibres.

Question 75

What causes muscular fatigue?

A) lactic acid accumulation
B) depletion of calcium
C) depletion of sodium
D) glycogenesis

Question 76

Fatigue is the failure of a muscle fibre to maintain what as a result of previous contractile activity?

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

Question 77

What is a characteristic feature of isometric muscle contractions?

A) They occur at constant tension.
B) The muscle shortens.
C) They are used for body movements.
D) They occur at constant length.

Question 78

Which statement is correct for fast-glycolytic (type IIb)fibres?

A) They contain an abundance of mitochondria.
B) They can be converted into fast-oxidative fibres by regular endurance activities.
C) They are most abundant in muscles specialized for maintaining low-intensity contractions for long periods of time without fatigue.
D) The muscle fibre diameter is small.

Question 79

What happens when a muscle atrophies?

A) The muscle fibres split lengthwise.
B) The muscle decreases in mass and becomes weaker.
C) The muscle fibres increase in diameter.
D) The muscle fibres undergo mitotic cell division.

Question 80

For which activity are submaximal isometric contractions important?

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