Deck 12: Muscle Physiology

Question 1

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

A) myofibril
B) fascicle
C) aponeurosis
D) tendon
E) ligament

Answer 1

D

Question 2

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

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

Answer 2

C

Question 3

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

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

Answer 3

C

Question 4

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

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

Question 5

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

A) The motor end plate is relatively large compared with other synapses.
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) Each muscle fiber is innervated by multiple motor neurons.
E) Every action potential that reaches the axon terminal of the motor neuron will generate an action potential in the healthy muscle fiber.

Question 6

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

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

Question 7

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

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

Question 8

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

Question 9

Increases in the amount of cytoplasmic calcium required to initiate a muscle contraction are mediated by the coupling between a the sarcoplasmic reticulum.

A) calcium pump : ryanodine receptor on the T tubule and a
_ on the membrane of
B) dihydropyridine receptor : calcium pump
C) ryanodine receptor : calcium pump
D) dihydropyridine receptor : ryanodine receptor
E) calcium -induced calcium release channel : dihydropyridine receptor

Question 10

A skeletal muscle is composed of a bundle of wrapped by connective tissue.

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

Question 11

What is the region of the striated muscle's banding patterns that contains only the connections between the tails of myosin molecules and is the mid -point of the sarcomere?

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

Question 12

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

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

Question 13

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

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

Question 14

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

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

Question 15

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

A) afferent
B) motor
C) autonomic
D) sympathetic
E) parasympathetic

Question 16

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

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

Question 17

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

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

Question 18

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

A) the condensation of ATP
B) binding to actin
C) binding to ATP only
D) the hydrolysis of ATP
E) binding to titin

Question 19

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

A) oxidative phosphorylation
B) crossbridge cycling
C) the sliding -filament model
D) excitation -contraction coupling
E) myoaction coupling

Question 20

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

A) actin and myosin acting as a spring using the energy stored by the stretching.
B) the passive interaction between actin and myosin (no energy required).
C) the elastic connective tissue that surrounds the muscle cells and fascicles.
D) the active interaction between actin and myosin (energy required).
E) titin acting as a spring using the energy stored by the stretching.

Question 21

Which is the longest phase of a twitch?

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

Question 22

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

A) They are always depolarizations.
B) They are graded potentials.
C) They are terminated by removal of acetylcholine from the synaptic cleft.
D) They are a result of acetylcholine binding to muscarinic cholinergic receptors.
E) They are almost always of sufficient magnitude to generate an action potential in the sarcolemma.

Question 23

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

Question 24

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

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

Question 25

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

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

Question 26

When an action potential is generated within a motor neuron,

A) all of the muscle cells within the motor unit are stimulated to relax.
B) the muscle cells of the motor unit will occasionally contract.
C) only select muscle cells within the motor unit are stimulated to contract.
D) every muscle cell of the motor unit is stimulated to contract.
E) the muscle cells from a neighboring motor unit will contract.

Question 27

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) ryanodine channels.
C) dihydropyridine receptors.
D) calcium -sequestering proteins in the cytoplasm.
E) calcium pumps (active transport of calcium).

Question 28

What is a motor unit?

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

Question 29

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

A) the myosin head to interact with calcium channels, triggering calcium release from the sarcoplasmic reticulum
B) the myosin head to detach from actin
C) the myosin head to attach to actin
D) the myosin head to be in its high -energy form
E) the myosin head to swing forward pulling actin toward the M line

Question 30

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

A) equivalent calcium released by each action potential
B) all -or -nothing property of the action potential generated by a skeletal muscle
C) equivalent calcium reuptake by the sarcoplasmic reticulum
D) equal numbers of crossbridges activated by the calcium released
E) equivalent activation of calmodulin stimulating myosin light -chain kinase activity

Question 31

Which of the following best describes the interaction between transverse (T) tubules and the sarcoplasmic reticulum in skeletal muscle contraction?

A) Action potentials in T tubules trigger the release of norepinephrine, which binds to receptors on the sarcoplasmic reticulum and triggers calcium release.
B) 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.
C) Action potentials in T tubules are detected by ryanodine receptors, which are coupled to DHP receptors in the sarcoplasmic reticulum and open channels for calcium.
D) Action potentials in T tubules cause a depolarization of the sarcoplasmic reticulum membrane, thereby opening calcium channels to trigger calcium release.
E) Action potentials in T tubules trigger the release of acetylcholine, which binds to receptors on the sarcoplasmic reticulum and triggers calcium release.

Question 32

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

Question 33

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

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

Question 34

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) Actin and myosin are synthesized here.
E) They conduct action potentials from the sarcolemma to the interior of the muscle cell.

Question 35

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

A) There is a slow increase in force with no change in muscle length.
B) Load is less than the force generated by the muscle.
C) There is a rapid increase in force with no change in muscle length.
D) Load is greater than the force generated by the muscle.
E) Muscle length will be increased by contraction.

Question 36

What enzyme catalyzes the reaction that creates creatine phosphate?

A) creatine hydrogenase
B) creatine phosphatase
C) creatine hydrolase
D) ATP hydrolase
E) creatine kinase

Question 37

Which of the following best describes an isotonic contraction?

A) When the contractile elements lengthen, they shorten the elastic elements and move the load.
B) When the contractile elements lengthen, they lengthen the elastic elements but do not move the load.
C) When the contractile elements shorten, they create enough force to 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 lengthen the elastic elements but do not move the load.

Question 38

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

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

Question 39

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) increase creatine phosphate concentration
C) increase ATP generation
D) decrease creatine kinase activity
E) decrease creatine phosphate concentration

Question 40

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) The binding of calcium to a low -affinity site closes sarcoplasmic reticulum calcium channels.
D) Sarcolemmal calcium channels open to allow the efflux of calcium.
E) A calcium pump actively removes calcium.

Question 41

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

A) random
B) asynchronous
C) asymmetrical
D) symmetrical
E) synchronous

Question 42

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

A) Slow oxidative fibers are the smallest diameter fibers.
B) Fast glycolytic fibers are the largest diameter fibers.
C) Slow oxidative fibers are quick to fatigue.
D) Fast oxidative fibers have a high mitochondrial density.
E) Fast glycolytic fibers produce their ATP by glycolysis.

Question 43

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

A) Summation and tetanus result in greater tension in the muscle.
B) Summation and tetanus result from increases in cytosolic calcium levels.
C) The maximum tension developed during summation and tetanus is treppe.
D) Summation and tetanus occur at high frequencies of skeletal muscle stimulation.
E) Summation and tetanus do not occur in cardiac muscle.

Question 44

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

A) 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.
B) the amount of calcium released by the sarcoplasmic reticulum is reduced as length increases.
C) the thin filaments are pulled away from one another, thereby reducing their ability to interact with myosin.
D) the thick filaments are pulled away from one another, thereby reducing their ability to interact with actin.
E) the thick filaments overlap one another, thereby reducing their ability to interact with actin.

Question 45

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

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

Question 46

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) myosin
D) myoglobin
E) lactic acid

Question 47

The mechanism responsible for the size principle involves

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

Question 48

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

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

Question 49

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

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

Question 50

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

Question 51

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

A) the thin filaments overlap one another, thereby reducing their ability to interact with myosin.
B) the amount of calcium released by the sarcoplasmic reticulum is reduced as length increases.
C) the thin filaments are pulled away from the thick filaments, thereby reducing actin's ability to interact with myosin.
D) the thick filaments overlap one another, thereby reducing their ability to interact with actin.
E) the thick filaments are pulled away from one another, thereby reducing their ability to interact with actin.

Question 52

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

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

Question 53

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

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

Question 54

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

A) adductor
B) flexor
C) insertion
D) abductor
E) origin

Question 55

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

A) the muscle will stop shortening once the force is greater than the load.
B) the muscle will continue to shorten until the force generated by the muscle stops increasing.
C) the amount of force generated by the muscle will continue to increase.
D) the amount of force generated by the muscle will start to decrease.
E) the amount of force generated by the muscle will remain constant.

Question 56

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

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

Question 57

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

Question 58

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

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

Question 59

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) treppe
C) twitch
D) recruitment
E) summation

Question 60

What causes some muscle fibers to appear red and dark?

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

Question 61

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 62

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 63

What type of receptor detects muscle length?

A) DHP
B) muscle spindle
C) Golgi tendon organ
D) ryanodine
E) nociceptor

Question 64

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

A) an increase in the blood supply to the muscles
B) an increase in the number of myofibrils per muscle fiber
C) a conversion of fast glycolytic fibers to fast oxidative fibers
D) an increase in the aerobic capacity of muscle
E) an increase in the number of mitochondria per muscle fiber

Question 65

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

Question 66

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

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

Question 67

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

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

Question 68

What type of efferent neuron innervates intrafusal muscle fibers?

A) type Ia
B) type Ib
C) type II
D) alpha motor neurons
E) gamma motor neurons

Question 69

What is an annulospiral ending?

A) sensory endings in the Golgi tendon organ that detect muscle tension
B) a structure in the utricle that contains hair cells
C) a structure in the semicircular canals that contains hair cells
D) sensory endings in the muscle spindle that detect muscle length
E) a structure in the cochlea that contains hair cells

Question 70

The interaction between actin and myosin in smooth muscle requires

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

Question 71

Which of the following could cause a pacemaker potential?

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

Question 72

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

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

Question 73

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

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

Question 74

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

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

Question 75

What connects muscles to bone?

A) T tubules
B) cartilage
C) ligaments
D) capillaries
E) tendons

Question 76

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

A) an increase in mitochondrial density
B) an increase in capillary density
C) an increase in the concentration of oxidative enzymes
D) an increase in the diameter of the skeletal muscle fibers
E) an increase in the number of oxidative fibers

Question 77

Relative to the triceps muscle, the biceps is its

A) agonist.
B) antagonist.
C) insertion.
D) origin.
E) abductor.

Question 78

Which of the following is true of ALL muscle types?

A) Recruitment increases the strength of contraction.
B) They contain calmodulin.
C) They contract by using the sliding filament mechanism and crossbridge cycling.
D) They contain T tubules.
E) They are striated.

Question 79

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

A) fast oxidative skeletal muscle
B) cardiac muscle
C) slow oxidative skeletal muscle
D) smooth muscle
E) fast glycolytic skeletal muscle

Question 80

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

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