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Physiology Exam 2 > Chapter 9 - Muscle > Flashcards

Chapter 9 - Muscle Flashcards

1
Q

Each actin filament is composed of
A) a single strand of actin molecules.
B) two strands of actin molecules wrapped together.
C) three strands of actin molecules wrapped together.
D) four strands of actin molecules wrapped together.
E) hundreds of strands of actin molecules wrapped together.

A

B) two strands of actin molecules wrapped together.

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2
Q

As actin and myosin filaments slide past each other during muscle contraction,
A) actin filaments shorten, while myosin filaments do not.
B) myosin filaments shorten, while actin filaments do not.
C) either actin or myosin filaments shorten, but not both at the same time.
D) both actin and myosin filaments shorten.
E) neither actin nor myosin filaments shorten.

A

E) neither actin nor myosin filaments shorten.

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3
Q

Which of the following statements about the “heads” of the myosin molecules is TRUE?
A) they form permanent links with actin filaments
B) they can attach to different sites on the actin filament
C) they straighten the myosin filaments
D) they allow the myosin filaments to wrap around each other
E) none of the above

A

B) they can attach to different sites on the actin filament

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4
Q

True or False: Each myosin protein has a globular head that extends outward from the myosin filament.

A

True

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5
Q

True or False: Unflexing of the myosin head requires ATP.

A

True

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6
Q

Muscle contraction is caused by
A) actin filaments sliding past each other.
B) myelin filaments sliding past each other.
C) myosin filaments sliding past each other.
D) actin filaments sliding past myelin filaments.
E) actin filaments sliding past myosin filaments.

A

E) actin filaments sliding past myosin filaments.

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7
Q

Which of the following statements about H zones and I bands is TRUE?
A) the H zones contain only myosin, while the I bands contain only actin
B) the H zones contain only actin, while the I bands contain only myosin
C) the H zones contain only myosin, while the I bands contain both actin and myosin
D) the H zones contain both actin and myosin, while the I bands contain only actin
E) the H zones and the I bands each contain both actin and myosin

A

A) the H zones contain only myosin, while the I bands contain only actin

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8
Q

During muscle contraction
A) the A band remains the same and the I band narrows.
B) the I band remains the same and the A band narrows.
C) both the A band and I band remain the same.
D) both the A band and I band narrow.
E) both the A band and I band become wider.

A

A) the A band remains the same and the I band narrows.

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9
Q

True or False: In a contracting muscle the Z lines come closer together.

A

True

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10
Q

True or False: In a relaxed muscle, the H zone is at its narrowest width.

A

False

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11
Q

Low cytosolic calcium = ______ muscle; High cytosolic calcium = ______ muscle.

A

Low = RELAXED; high = ACTIVATED (cross-bridged binding sites are exposed)

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12
Q 
During contraction of a muscle, calcium ions bind to...
	A)	the actin myofilament.
	B)	the troponin molecule.
	C)	the tropomyosin molecule.
	D)	the sarcoplasmic reticulum.
	E)	the sarcolemma.
A

B) the troponin molecule.

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13
Q

The bond between the actin and myosin head is broken when…
A) an ATP molecule binds to the myosin head.
B) an ATP molecule binds to the actin molecule.
C) an ATP molecule breaks down on the myosin head.
D) an ATP molecule breaks down on the actin molecule.
E) ADP and phosphate bind to the myosin head.

A

A) an ATP molecule binds to the myosin head.

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14
Q

Energy is released when…
A) ADP is broken down into ATP and phosphate.
B) ATP is broken down into ADP and phosphate.
C) ADP and phosphate combine to form ATP.
D) ATP and phosphate combine to form ADP.
E) AMP and two phosphates combine to form ATP.

A

B) ATP is broken down into ADP and phosphate

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15
Q

True or False: The sequence of cross bridge formation and myofilament movement will be repeated as long as calcium ions are present.

A

True

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16
Q

True or False: When cross bridges form and the muscle fibers contract, the actin myofilament slides past the myosin myofilament.

A

True

17
Q

True of False: ATP is an allosteric regulator, but is NOT a covalent regulator.

A

FALSE. ATP is both an allosteric and covalent regulator

  • Hydrolysis of ATP by myosin energizes the cross-bridges, providing the energy for force generation (covalent action)
  • Binding of ATP to myosin dissociates cross-bridges bound to actin, allowing the bridges to repeat their cycle of activity (allosteric action)
18
Q 
Where does the calcium for the cross-bridge formation come from?
A) Extracellular Ca
B) Intracellular Ca
C) Intraorganelle (SR) Ca
D) All of the above
A

C) Intraorganelle Ca - the source of calcium in skeletal muscle comes exclusively from the sarcoplasmic reticulum (SR)

19
Q 
An action potential enters a neuron...
	A)	by diffusion.
	B)	by the T-tubules.
	C)	by the sarcolemma.
	D)	by the sarcoplasmic reticulum.
	E)	by the actin myofilament.
A

B) by the T-tubules.

20
Q 
What structures do the calcium ions bind to when muscle contraction is initiated?
	A)	the actin myofilament.
	B)	the troponin molecule.
	C)	the tropomyosin molecule.
	D)	the sarcoplasmic reticulum.
	E)	the sarcolemma.
A

B) the troponin molecule.

21
Q

Cross bridges form between…
A) troponin and tropomyosin.
B) calcium and sodium.
C) the sarcolemma and the sarcoplasmic reticulum.
D) the T-tubules and the sarcolemma.
E) the actin filaments and the myosin heads.

A

E) the actin filaments and the myosin heads.

22
Q

True or False: An action potential introduced at the neuromuscular junction is propagated along the sarcoplasmic reticulum.

A

False

23
Q

True or False: In response to an action potential entering the neuron, calcium ions diffuse from the sarcolemma into the sarcoplasm.

A

False

24
Q

An action potential arriving at the presynaptic terminal causes…
A) voltage-gated sodium ion channels to open, and sodium ions to diffuse into the cell.
B) voltage-gated calcium ion channels to open, and calcium ions to diffuse out of the cell.
C) voltage-gated calcium ion channels to open, and calcium ions to diffuse into the cell.
D) acetylcholine to diffuse into the cell.
E) ligand-gated sodium channels to open, and sodium ions to diffuse out of the cell.

A

C) voltage-gated calcium ion channels to open, and calcium ions to diffuse into the cell.

25
Q

In the neuromuscular junction, acetylcholine…
A) diffuses across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic muscle fiber.
B) is actively transported across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic muscle fiber.
C) diffuses across the synaptic cleft and causes calcium ions to diffuse into the postsynaptic muscle fiber.
D) diffuses across the synaptic cleft and causes sodium ions to diffuse out of the postsynaptic muscle fiber.
E) is actively transported across the synaptic cleft and causes calcium ions to diffuse into the postsynaptic muscle fiber.

A

A) diffuses across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic muscle fiber.

26
Q

The neurotransmitter in the neuromuscular junction…
A) causes ligand gated calcium channels in the muscle fiber to increase their permeability to calcium, which depolarizes the postsynaptic membrane.
B) causes ligand gated sodium channels in the muscle fiber to increase their permeability to sodium, which depolarizes the postsynaptic membrane.
C) increases the calcium ion permeability of the presynaptic membrane.
D) increases the sodium ion permeability of the presynaptic membrane.
E) depolarizes the presynaptic membrane by increasing the permeability of sodium ions.

A

B) causes ligand gated sodium channels in the muscle fiber to increase their permeability to sodium, which depolarizes the postsynaptic membrane.

27
Q

True or False: Acetylcholine is broken down into acetic acid and cholinesterase by choline.

A

False; acetylcholine is broken down into acetic acid and choline in the synaptic cleft by acetylcholinesterase

28
Q

True or False: Once threshold is reached on the postsynaptic membrane, an action potential is generated and propagated over the muscle cell membrane.

A

True

29
Q

An action potential arriving at the presynaptic terminal causes…
A) sodium ions to diffuse into the cell.
B) sodium ions to diffuse out of the cell.
C) calcium ions to diffuse into the cell.
D) acetylcholine to diffuse into the cell.
E) ligand-gated sodium channels to open.

A

C) calcium ions to diffuse into the cell.

30
Q

The functional unit of muscular contraction is the ____ ____.

A

Motor Unit

*defined as the motor neuron and all of the muscle fibers that it innevates

31
Q

What are the three differences between motor units?

A

Speed of contraction, Strength of contraction, and Endurance of contraction

32
Q

Which of the following is FALSE when comparing action potentials of skeletal and cardiac muscle:
A) Both have fast sodium conductance (I Na
B) K+ conductance DECREASES in skeletal and INCREASES in cardiac muscle AP
C) A large and long-lasting (L-type) Ca++ conductance is unique to the cardiac AP
D) ALL of these conductances are voltage-sensitive channels

A

B) K+ conductance increases in skeletal and decreases in cardiac muscle action potentials

33
Q

True or False: Length-tension curve is much narrower in smooth muscle than in skeletal muscle.

A

FALSE - the curve is much broader in smooth muscle

34
Q 
A person who sprints for 45 seconds obtains most of their energy from
	A)	muscle triglycerides.
	B)	plasma free fatty acids.
	C)	blood glucose.
	D)	muscle glycogen.
A

D) muscle glycogen.

35
Q 
What happens to the amount of muscle glycogen used for energy as exercise continues?
	A)	it increases
	B)	it decreases
	C)	it continues unchanged
	D)	it is never used
A

B) it decreases

36
Q

After 3 hours of exercise what are the main sources of energy?
A) blood glucose and plasma free fatty acids
B) blood glucose and muscle glycogen
C) blood glucose and muscle triglycerides
D) muscle glycogen and muscle triglycerides

A

A) blood glucose and plasma free fatty acids

37
Q 
What happens to the amount of plasma free fatty acids used for energy as exercise continues?
	A)	they increase
	B)	they decrease
	C)	they continue unchanged
	D)	they are never used
A

A) they increase

38
Q 
Where are most plasma free fatty acids obtained from?
	A)	hydrolysis of blood glucose
	B)	hydrolysis of muscle triglycerides
	C)	hydrolysis of stored fat
	D)	sports beverages
A

C) hydrolysis of stored fat

Physiology Exam 2 (4 decks)

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