L04/05 Muscle Physiology Flashcards by tip gee

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

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

D) actin

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

D) sarcomere : Z lines

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

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

C) troponin

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

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

C) the sarcomeres shortening (I & H bands)

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

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

A) crossbridge cycling

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

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

D) the hydrolysis of ATP

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

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

B) power stroke

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

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

E) binding of ATP to myosin

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

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

D) excitation-contraction coupling

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

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

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

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

C) motor neurons

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

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

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

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

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

B) I band

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

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

B) the myosin head to detach from actin

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

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

E) Each muscle fiber is innervated by multiple motor neurons.

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

B) dihydropyridine receptor : ryanodine receptor

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

A) dihydropyridine receptor

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

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

C) 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.

What is the function of T tubules?

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

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

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

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

A) calcium pumps (active transport of calcium)

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

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

A) Sarcolemmal calcium channels open to allow the efflux of calcium.

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

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

C) every muscle cell of the motor unit is stimulated to contract

Which is the longest phase of a twitch?

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

D) relaxation

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

C) equivalent activation of calmodulin stimulating myosin light-chain kinase activity

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

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

Which of the following statements about end-plate potentials is FALSE? A) They are graded potentials. B) They are always depolarizations. C) They are always of sufficient magnitude to generate an action potential in the sarcolemma. D) They are a result of acetylcholine binding to muscarinic cholinergic receptors. E) They are terminated by removal of acetylcholine from the synaptic cleft.

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

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) Summation C) Force-velocity relationship D) External tension E) Internal tension ```

B) Summation

The tension produced during skeletal muscle contraction can be increased by all of the following except one. Which one is it? A) recruiting motor units B) increasing the frequency of action potentials in the motor neuron innervating the muscle C) increasing the frequency of action potentials in the muscle fiber D) initiating the contraction when the muscle is at its optimum length E) increasing the load on the muscle

E) increasing the load on the muscle

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

E) The maximum tension developed during summation and tetanus is treppe.

As skeletal muscle is further stretched beyond the length where optimum force is developed, ________. A) the amount of calcium released by the sarcoplasmic reticulum is reduced as length increases B) the thin filaments are pulled away from one another, thereby reducing their ability to interact with myosin C) the thick filaments are pulled away from one another, thereby reducing their ability to interact with actin D) the thick filaments overlap one another, thereby reducing their ability to interact with actin E) the thin filaments overlap one another, thereby reducing their ability to interact with myosin

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

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

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

Which of the following does NOT influence the force generated by an individual muscle fiber? ``` A) frequency of stimulation B) fiber diameter C) length at onset of contraction Which of the following does NOT influence the force generated by an individual muscle fiber? A) frequency of stimulation B) fiber diameter C) length at onset of contraction D) recruitment E) summation ``` E) summation

D) recruitment

What is an increase in the number of active motor units that would increase the force developed by a skeletal muscle called? ``` A) Recruitment B) Summation C) Treppe D) Tetanus E) Length-tension relationship ```

A) Recruitment

Which of the following is true of ALL muscle types? A) contract by using the sliding filament mechanism and cross-bridge cycling B) are striated C) contain T tubules D) contain calmodulin E) recruitment increases the strength of contraction

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

In smooth muscle, calcium triggers contraction by binding to what protein? ``` A) troponin B) myosin light chain kinase C) myosin light chain D) calmodulin E) DHP receptors ```

D) calmodulin

Calcium binding to calmodulin causes phosphorylation 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 ```

E) myosin in smooth muscle only

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

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

Binding of ATP to myosin increases myosin's affinity for actin. (T/F)

False, decreases affinity

As skeletal muscle shortens with contraction, the length of the I band remains constant as the length of the A band decreases. (T/F)

False, The I and H band shorten, The A band is the myosin filament.

The primary source of calcium that drives skeletal muscle contraction is the sarcoplasmic reticulum. (T/F)

True

Ryanodine receptors are calcium channels in the sarcoplasmic reticulum. (T/F)

True

The contraction phase of a twitch lasts longer than the relaxation phase. (T/F)

False, the relation phase lasts longer.

Skeletal muscle fibers operate at near-optimal sarcomere length in situ. (T/F)

True

Action potentials in cardiac muscle last longer than action potentials in skeletal muscle. (T/F)

True