Deck 12: Muscle Physiology

Question 1

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

A)adenylate cyclase.
B)myosin light- chain phosphatase.
C)tyrosine kinase.
D)calmodulin ATPase.
E)myosin light- chain kinase.

Answer 1

E

Question 2

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

A)large motor neurons : large motor unit : last to be recruited
B)large motor neurons : small motor unit : first to be recruited
C)large motor neurons : large motor unit : first to be recruited
D)large motor neurons : small motor unit : last to be recruited
E)There is no relationship.

Answer 2

A

Question 3

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

A)sarcomere : M lines
B)sarcomere : Z lines
C)crossbridge : Z lines
D)crossbridge : A bands
E)sarcomere : I bands

Answer 3

B

Question 4

Which of the following could cause a pacemaker potential?

A)spontaneous closing of calcium channels
B)spontaneous opening of potassium channels
C)spontaneous opening of sodium channels
D)spontaneous opening of chloride channels
E)All of the answers are correct.

Question 5

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

A)Crossbridge cycling is asynchronous between a certain thick and thin filament.
B)No more than one myosin head links to the thin filament at the same time.
C)No more than one myosin head detaches from the thin filament at the same time.
D)Tropomyosin only exposes one binding site on actin at a time allowing only one crossbridge to form with actin at a given time.
E)Crossbridge cycling is highly synchronized between a certain thick and thin filament.

Question 6

What causes some muscle fibers to appear red and dark?

A)presence of myoglobin and lots of mitochondria
B)greater blood supply
C)high concentration of actin and myosin
D)presence of lots of mitochondria
E)presence of myoglobin

Question 7

Which is the longest phase of a twitch?

A)plateau
B)latent
C)initial
D)contraction
E)relaxation

Question 8

The interaction between actin and myosin in smooth muscle requires

A)the tropomyosin must be moved out of the way by troponin before myosin can bind to actin.
B)the interaction between calcium and troponin to expose the myosin binding site on the actin molecule.
C)that the calcium- calmodulin complex directly phosphorylates myosin light chain, allowing myosin to bind to actin.
D)that the calcium- calmodulin complex activates myosin light- chain kinase, which phosphorylates myosin thereby allowing it to bind with actin.
E)the activation of troponin, which stimulates myosin light- chain kinase to phosphorylate myosin light chain, allowing myosin to bind with actin.

Question 9

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

A)Z line interaction
B)titin cycling
C)the sliding- filament model
D)sarcomeric facilitation
E)crossbridge cycling

Question 10

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

A)tropomyosin
B)myosin
C)titin
D)troponin
E)actin

Question 11

Troponin is a complex of three proteins that bind to tropomyosin, calcium, and

A)transverse tubule.
B)tropomyosin.
C)troponin.
D)actin.
E)sarcoplasmic reticulum.

Question 12

Where are gap junctions commonly found?

A)single- unit smooth muscle only
B)multi- unit smooth muscle only
C)cardiac muscle only
D)both single- unit smooth muscle and cardiac muscle
E)both single- unit and multi- unit smooth muscle

Question 13

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

A)dihydropyridine receptor
B)sodium channel
C)calcium pump
D)calcium- induced calcium release channel
E)ryanodine receptor

Question 14

Calcium binding to calmodulin causes phosphorylation by myosin light chain kinase of what protein in what type of muscle?

A)troponin in skeletal and cardiac muscle only
B)troponin in smooth muscle only
C)actin in cardiac and smooth muscle
D)actin in smooth muscle only
E)myosin in smooth muscle only

Question 15

Which type of skeletal muscle fiber has most of its energy come from substrate- level phosphorylation?

A)fermentative
B)glycolytic
C)oxidative
D)fast
E)slow

Question 16

The mechanism responsible for the size principle involves

A)larger sympathetic neurons that contain the greatest number of muscle cells and reach threshold easier than smaller neurons.
B)smaller motor neurons that innervate the least number of muscle cells and reach threshold easier than larger neurons.
C)larger motor neurons that innervate the greatest number of muscle cells and reach threshold easier than smaller neurons.
D)smaller motor units that contain the greatest number of muscle cells and reach threshold easier than larger neurons.
E)smaller sympathetic neurons that contain the least number of muscle cells and reach threshold easier than larger neurons.

Question 17

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

A)fast glycolytic : slow oxidative : fast oxidative
B)slow oxidative : fast glycolytic : fast oxidative
C)fast oxidative : fast glycolytic : slow oxidative
D)slow oxidative : fast oxidative : fast glycolytic
E)fast glycolytic : fast oxidative : slow oxidative

Question 18

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

A)hemoglobin
B)myosin light chain
C)myoglobin
D)lactic acid
E)myosin

Question 19

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

A)fiber diameter
B)summation
C)length at onset of contraction
D)frequency of stimulation
E)recruitment

Question 20

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

A)the thin filaments shortening
B)the sarcomeres shortening
C)the thick filaments shortening
D)the A bands shortening
E)the Z lines not changing their position

Question 21

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

A)fatigue
B)wasting
C)treppe
D)tetanus
E)O2 depletion

Question 22

Calcium binds to calmodulin where?

A)smooth and cardiac muscle only
B)skeletal muscle only
C)skeletal and smooth muscle only
D)skeletal, smooth, and cardiac muscle
E)smooth muscle only (single- unit or multi- unit)

Question 23

What is a motor unit?

A)all the myofibrils in a muscle fiber
B)all the muscle fibers in a fascicle
C)a muscle fiber and all the motor neurons that innervate it
D)a spinal nerve and all the muscle fibers it innervates
E)a motor neuron and all the muscle fibers it innervates

Question 24

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

A)troponin
B)transverse tubule
C)tropomyosin
D)actin
E)sarcoplasmic reticulum

Question 25

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

A)calcium- binding proteins on the sarcoplasmic reticulum.
B)calcium pumps (active transport of calcium).
C)calcium- sequestering proteins in the cytoplasm.
D)ryanodine channels.
E)dihydropyridine receptors.

Question 26

Where does calcium bind to troponin?

A)skeletal and cardiac muscle only
B)skeletal muscle only
C)skeletal and smooth muscle only
D)smooth and cardiac muscle only
E)smooth muscle only (single- unit or multi- unit)

Question 27

Intercalated disks contain what type of special junctions?

A)tight junctions only
B)both gap junctions and tight junctions
C)hemidesmosomes
D)desmosomes
E)gap junctions only

Question 28

Which of the following stores calcium to be released for muscle contraction?

A)actin and myosin
B)tendons
C)motor end plate
D)sarcoplasmic reticulum
E)sarcomeres

Question 29

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

A)much less than optimum length.
B)near optimal.
C)3 microns.
D)quite variable from one muscle to the next.
E)much greater than optimum length.

Question 30

A skeletal muscle is composed of a bundle of , each composed of many muscle fibers wrapped by connective tissue.

A)myofibrils
B)muscle cells
C)sarcomeres
D)fascicles
E)myofilaments

Question 31

What is the antagonistic muscle to the triceps?

A)posterior deltoid
B)brachialis
C)biceps
D)quadriceps
E)coracobrachialis

Question 32

Mechanisms whereby force of skeletal muscle fibers can be altered include all of the following EXCEPT

A)recruitment.
B)conversion of myosin ATPase type.
C)frequency of stimulation (summation).
D)fiber diameter (sarcomeres in parallel).
E)fiber length.

Question 33

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

A)more sarcomeres in series
B)fewer myofibrils per muscle cell
C)more sarcomeres in parallel
D)fewer sarcomeres in series
E)fewer sarcomeres in parallel

Question 34

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

A)slide past one another.
B)shorten.
C)lengthen.
D)condense.
E)do not interact.

Question 35

What is the enzyme that modulates the ability of myosin to bind actin in smooth muscle?

A)calmodulin
B)troponin
C)titin
D)tropomyosin
E)myosin light- chain kinase

Question 36

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

A)development of rigor
B)cocking of the myosin head
C)binding of actin to myosin
D)power stroke
E)breaking of the actin myosin complex

Question 37

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?

A)tetanus
B)twitch
C)treppe
D)summation
E)recruitment

Question 38

During intense (heavy)exercise, the initial ability of oxidative phosphorylation to provide enough ATP for the sudden demand of increased force generation by the skeletal muscle is , thereby causing the muscle fiber to quickly and massively boost its energy production from until oxygen delivery and other mechanisms come up to speed.

A)inadequate : substrate- level phosphorylation
B)enhanced : fatty acids
C)enhanced : substrate- level phosphorylation
D)enhanced : glucose
E)inadequate : fatty acids

Question 39

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

A)the movement of tropomyosin, thereby exposing the myosin- binding site on the actin molecule
B)the binding of ATP to myosin
C)the hydrolysis of ATP
D)the movement of tropomyosin, thereby exposing the actin- binding site on the myosin molecule
E)the further release of calcium into the cytoplasm

Question 40

What is the functional unit of skeletal muscle?

A)tendons
B)actin and myosin
C)sarcomeres
D)motor end plate
E)sarcoplasmic reticulum

Question 41

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?

A)length- tension relationship
B)internal tension
C)summation
D)force- velocity relationship
E)external tension

Question 42

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?

A)increase glucose metabolism
B)decrease creatine phosphate concentration
C)increase ATP generation
D)decrease creatine kinase activity
E)increase creatine phosphate concentration

Question 43

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

A)latent period
B)absolute refractory period
C)reticence
D)relative refractory period
E)synaptic delay

Question 44

Which of the following generates the mechanical force of a muscle through crossbridge cycling?

A)sarcomeres
B)motor end plate
C)sarcoplasmic reticulum
D)actin and myosin
E)tendons

Question 45

Which of the following contains ryanodine receptors?

A)sarcomeres
B)motor end plate
C)sarcoplasmic reticulum
D)actin and myosin
E)tendons

Question 46

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)?

A)the amount of neurotransmitter released into the synaptic cleft
B)the presynaptic modulation of the autonomic neurons
C)the duration of neurotransmitter release from the autonomic neurons
D)the neurotransmitter released by the autonomic nervous system
E)the type of receptor present on the effector organ

Question 47

Which type of skeletal muscle fiber catalyzes hydrolysis of ATP slowly?

A)slow
B)glycolytic
C)oxidative
D)fast
E)fermentative

Question 48

Calcium is stored in what region of skeletal muscle cells?

A)actin
B)troponin
C)tropomyosin
D)sarcoplasmic reticulum
E)transverse tubule

Question 49

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

A)Alpha motor neurons are activated before gamma motor neurons.
B)Alpha and gamma motor neurons are activated at the same time.
C)During light activity, alpha motor neurons are activated first; during heavy activity, gamma motor neurons are activated first.
D)Gamma motor neurons are activated before alpha motor neurons.
E)During light activity, gamma motor neurons are activated first; during heavy activity, alpha motor neurons are activated first.

Question 50

What are the elastic fibers that anchor thick filaments in place?

A)titin
B)myosin light- chain kinase
C)calmodulin
D)tropomyosin
E)troponin

Question 51

What anchors thick filaments together?

A)M line
B)I band
C)A band
D)Z line
E)H zone

Question 52

What is the function of T tubules?

A)They store calcium.
B)They provide elasticity to the muscle.
C)They hold the thick filaments to the Z line.
D)They conduct action potentials from the sarcolemma to the interior of the muscle cell.
E)Actin and myosin are synthesized here.

Question 53

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

A)poor ability to produce ATP in the absence of oxygen
B)fewer capillaries
C)readily fatigable
D)high capacity for lactic acid production
E)absence of myoglobin

Question 54

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

A)summation
B)tetanus
C)treppe
D)length- tension relationship
E)recruitment

Question 55

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

A)calmodulin
B)DHP receptors
C)myosin light chain kinase
D)troponin
E)myosin light chain

Question 56

Which muscle type contains actin and myosin?

A)smooth and cardiac muscle only
B)skeletal muscle only
C)smooth muscle only (single- unit or multi- unit)
D)skeletal and smooth muscle only
E)skeletal, smooth, and cardiac muscle

Question 57

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

A)troponin.
B)tropomyosin.
C)the amount of energy available.
D)the type of myosin and its ATPase present.
E)actin.

Question 58

Heavy intensity exercise generates what byproduct that contributes to fatigue?

A)CO2
B)pyruvic acid
C)lactic acid
D)glycogen
E)fatty acids

Question 59

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

A)Oxidative fibers can be depleted of glycogen, their primary energy source.
B)Compression of muscle during contraction can reduce blood flow to the muscle.
C)Repeated action potentials along the same neuron can lead to neuromuscular fatigue.
D)Glycolytic fibers produce lactic acid and inhibit enzyme activity with their hydrogen ion.
E)The crossbridges can become resistant to ATP.

Question 60

What binds calcium in cardiac muscle cells?

A)calmodulin
B)myosin light- chain kinase
C)troponin
D)titin
E)tropomyosin

Question 61

Which type of skeletal muscle fiber contains a high concentration of mitochondria?

A)slow
B)oxidative
C)fast
D)glycolytic
E)fermentative

Question 62

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

A)An end- plate potential triggers an action potential on the sarcolemma.
B)DHP receptors on the T tubules detect changes in voltage and communicate to ryanodine receptors on the sarcoplasmic reticulum to open calcium channels.
C)Calcium binds to troponin, causing a shift in tropomyosin, thereby exposing the binding sites on actin for myosin.
D)Calcium ATPases in the sarcoplasmic reticulum are necessary for relaxation of the muscle.
E)An action potential in the sarcolemma stimulates the opening of voltage- gated calcium channels in the plasma membrane and the sarcoplasmic reticulum.

Question 63

As the intensity of exercise increases (and the potential gap between energy demand and creation threatens to widen), the muscles quickly underwrite their escalating energy demands by augmenting oxidative with substrate- level phosphorylation, resulting in the increased generation of which of the following?

A)fatty acid
B)ATP
C)glucose
D)lactic acid
E)water from the electron transport chain

Question 64

Which of the following best describes an isotonic contraction?

A)When the contractile elements lengthen, they lengthen the elastic elements but do not move the load.
B)When the contractile elements lengthen, they shorten the elastic elements and move the load.
C)When the contractile elements shorten, they lengthen the elastic elements but do not move the load.
D)The contractile elements stay the same length as the elastic elements shorten and move the load.
E)When the contractile elements shorten, they create enough force to move the load.

Question 65

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

A)Each muscle fiber is innervated by multiple motor neurons.
B)The terminal bouton fans out over a wide area of the sarcolemma.
C)There is a high density of acetylcholine receptors in the motor end plate.
D)Every action potential that reaches the axon terminal of the motor neuron will generate an action potential in the healthy muscle fiber.
E)The motor end plate is relatively large compared with other synapses.

Question 66

What region of thick filaments has no overlap with thin filaments?

A)Z line
B)H zone
C)A band
D)M line
E)I band

Question 67

Which of the following contains DHP receptors?

A)transverse tubules
B)tendons
C)motor end plate
D)sarcoplasmic reticulum
E)sarcomeres

Question 68

Which type of skeletal muscle fiber is white muscle?

A)slow
B)oxidative
C)fast
D)fermentative
E)glycolytic

Question 69

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

A)The amount of calcium bound to troponin decreases.
B)A myosin- binding site on the actin molecule is blocked by tropomyosin.
C)Sarcolemmal calcium channels open to allow the efflux of calcium.
D)A calcium pump actively removes calcium.
E)The binding of calcium to a low- affinity site closes sarcoplasmic reticulum calcium channels.

Question 70

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

A)Load is less than the force generated by the muscle.
B)rapid shortening of the muscle
C)rapid lengthening of the muscle
D)Load is equal to the force generated by the muscle.
E)Load is greater than the force generated by the muscle.

Question 71

Which of the following extends the length of the thick filaments?

A)A band
B)H zone
C)Z line
D)M line
E)I band

Question 72

The tension produced during skeletal muscle contraction can be increased by all of the following EXCEPT

A)initiating the contraction when the muscle is at its optimum length.
B)increasing the frequency of action potentials in the muscle fiber.
C)increasing the frequency of action potentials in the motor neuron innervating the muscle.
D)increasing the load on the muscle.
E)recruiting motor units.

Question 73

Which of the following appears as light bands under the microscope?

A)H zone
B)Z line
C)A band
D)M line
E)I band

Question 74

Gap junctions are present between which cells?

A)smooth muscle only (single- unit or multi- unit)
B)skeletal muscle only
C)skeletal, smooth, and cardiac muscle
D)smooth and cardiac muscle only
E)skeletal and smooth muscle only

Question 75

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

A)the thick filaments are pulled away from one another, thereby reducing their ability to interact with actin.
B)the amount of calcium released by the sarcoplasmic reticulum is reduced as length increases.
C)the thick filaments overlap one another, thereby reducing their ability to interact with actin.
D)the thin filaments are pulled away from one another, thereby reducing their ability to interact with myosin.
E)the thin filaments overlap one another with myosin bumping into the Z- line, thereby causing the force generated by crossbridges to be exerted on the sarcomere itself rather than transmitted to the ends of the muscle fiber.

Question 76

Which type of skeletal muscle fiber fatigues rapidly?

A)fast
B)glycolytic
C)oxidative
D)slow
E)isotonic

Question 77

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

A)Z line
B)M line
C)H zone
D)I band
E)A band

Question 78

Which of the following transmits action potentials to the interior of the muscle cell to trigger calcium release?

A)sarcomeres
B)motor end plate
C)actin and myosin
D)sarcoplasmic reticulum
E)tendons

Question 79

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.

A)ryanodine receptor : calcium pump
B)calcium pump : ryanodine receptor
C)calcium- induced calcium release channel : dihydropyridine receptor
D)dihydropyridine receptor : ryanodine receptor
E)dihydropyridine receptor : calcium pump

Question 80

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

A)binding of the troponin complex to actin
B)conformational change that occurs as the myosin head changes from the high to low energy state
C)binding of tropomyosin to myosin
D)binding of ATP to myosin
E)binding of ATP to actin