Deck 8: Muscle Physiology

Question 1

Within a muscle fiber the contractile elements may constitute as much as ______ of the cell volume.

A) 50%
B) 60%
C) 70%
D) 80%
E) 90%

Answer 1

90%

Question 2

The sarcomere lies within the boundaries of which of these structures?

A) A bands
B) H bands
C) I bands
D) sarcoplasmic reticulum
E) Z lines

Answer 2

Z lines

Question 3

The principal role of calcium in skeletal muscle contraction is to

A) participate in the propagation of an action potential along the surface of the muscle fiber.
B) bind troponin, which in turn permits tropomyosin to uncover the cross-bridge binding site on the thin filament.
C) bind tropomyosin, which in turn permits troponin to uncover the cross-bridge binding site on the thin filament.
D) activate a calcium-calmodulin-dependent protein kinase, which in turn phosphorylates and activates myosin.

Answer 3

bind troponin, which in turn permits tropomyosin to uncover the cross-bridge binding site on the thin filament.

Question 4

Which of the following observations confirms the sliding filament mechanism for muscle contraction?

A) As the sarcomere shortens, the H zone becomes smaller.
B) As the sarcomere shortens, the width of the A band remains the same.
C) As the sarcomere shortens, the I band becomes smaller.
D) Two of these.
E) All of these.

Question 5

In skeletal muscle depolarization of the T tubule membrane causes

A) activation of Ca²⁺ ATPase pumps which triggers a rise in intracellular calcium levels
B) dihydropyridine to bind calcium channel receptors which triggers a rise in intracellular calcium levels.
C) activation of stretch-activated Ca²⁺ channels which triggers a rise in intracellular calcium levels.
D) activation of dihydroxypyridine receptors in membrane of the T tubule which triggers a rise in intracellular calcium levels.
E) ryanodine to bind calcium channel receptors which triggers a rise in intracellular calcium levels.

Question 6

Which of the following choices most accurately represents the sequence of steps occurring in the contraction cycle? The events numbered 1 through 6 may be used more than once.
1) Mysoin binds ATP
2) Mysoin hydrolyzes ATP and goes into cocked position
3) Myosin releases ADP and inorganic phosphate
4) Myosin binds actin filament
5) Power stroke
6) Myosin releases actin filament

A) 1, 2, 3, 4, 5, 6, 1
B) 1, 2, 4, 3, 5, 1, 6
C) 1, 6, 2, 4, 3, 5, 1, 6
D) 1, 2, 6, 3, 4, 5, 6, 1
E) None of these.

Question 7

One way one can purify myosin from other skeletal muscle proteins is to immobilize actin on a column, pour a mix of the muscle proteins through, wash first to get out the nonspecific proteins and then do a second to wash to obtain myosin. Based on the contraction cycle, your first wash should

A) include ATP, but the second wash should not.
B) not include ATP, but the second wash should.
C) include ATP, as should the second wash.
D) not include ATP, and neither should the second.
E) should include calcium, but the second one should not.

Question 8

Which of the following statements is NOT true?

A) Rigor mortis occurs as a result of a rise in intracellular calcium concentrations.
B) In skeletal muscle a single action potential lasts about 5-10 msec.
C) In skeletal muscle the relaxation time lasts slightly longer than the contractile time.
D) In skeletal muscle the contractile response ceases when the lateral sacs take up Ca²⁺.
E) A spring can move much faster than a muscle can contract.

Question 9

Which of the following does NOT affect the tension that can be developed by a muscle fiber?

A) the number of motor units recruited
B) the frequency of action potentials conducted by the motor neuron
C) the length of the fiber at the onset of contraction
D) diameter of the muscle fiber
E) All of these affect tension development by a muscle fiber.

Question 10

Arthropod muscle differs from vertebrate muscle in that

A) a single muscle fiber may be innervated by multiple motor neurons.
B) a single motor neuron forms multiple synapses (multiterminal innervation) with a single muscle fiber.
C) development of muscle tension is modulated by inhibitory presynaptic inputs.
D) muscle fibers are innervated by both excitatory and inhibitory neurons.
E) All of these.

Question 11

In the length-tension curve shown, why does force decrease at sarcomere lengths less than l_o?

A) Not as much Ca²⁺ is released in a sarcomere with a length less than l_o..
B) Interference between actin filaments originating from opposite ends of the sarcomere prevents maximal or optimal cross-bridge formation.
C) The muscle fiber runs out of ATP.
D) In this situation, Ca²⁺ availability and the position of the actin filaments are responsible for the decrease in muscle shortening because ATP will still be available.
E) All of these contribute to reduced muscle shortening in a sarcomere with a length less than l_o.

Question 12

Which of the following is NOT true?

A) Muscle tension is produced internally within the sarcomeres.
B) Muscle tension is transmitted to the skeleton by tightening of the series-elastic component within the sarcomere.
C) It is possible for a skeletal muscle to produce movement without the muscle being attached to bone at both ends.
D) With respect to skeletal muscle, the load and velocity for shortening are inversely related for concentric contractions.
E) Actually, all of these are true statements.

Question 13

An isometric contraction is a contraction in which

A) tension (or force) increases, but length stays the same.
B) tension (or force) stays the same, but length increases.
C) tension (or force) stays the same, and length stays the same.
D) tension (or force) stays the same, but length decreases.
E) tension (or force) decreases, and length decreases.

Question 14

In an isotonic, concentric contraction,

A) circular muscles (like those in the iris of the eye) contract, making a smaller aperture.
B) muscle length shortens while tension remains constant.
C) muscle lengths shorten, drawing objects closer to the body midline.
D) None of these.

Question 15

Which of the following ATP-dependent steps of the contraction-relaxation cycle could be accomplished with a non-hydrolyzable form of ATP such as ATP- $\gamma$ -S for example?

A) cocking of the cross-bridge in anticipation of the power-stroke
B) release of actin by myosin
C) sequestration of calcium into the sarcoplasmic reticulum
D) All of these could be accomplished with ATP- $\gamma$ -S.
E) None of these could be accomplished with ATP- $\gamma$ -S.

Question 16

Creatine is an important metabolite in muscle physiology. Based on your understanding of its role in muscle energetics, which of the following statements is true?

A) The concentration of creatine rises as the concentration of ATP rises.
B) The concentration of creatine falls as the concentration of ATP rises.
C) The concentration of creatine is independent of the concentration of ATP.
D) The concentration of creatine rises as the concentration of ADP rises.

Question 17

How much of the energy available in ATP is lost as heat energy during an isotonic contraction by skeletal muscle?

A) 15%
B) 25%
C) 50%
D) 60%
E) 75%

Question 18

Fast muscle fibers differ from slow muscle fibers in that fast muscle fibers

A) are able to take up oxygen more quickly from the blood.
B) are equipped with a myosin-ATPase with more rapid kinetics.
C) are able to generate ATP more rapidly.
D) conduction action potentials more rapidly.
E) are recruited by the nervous system more rapidly.

Question 19

An advantage of the large fiber diameter of fast glycolytic muscle is

A) it's correlated with its large volume, which in turn means it can hold more oxygen, and generate ATP aerobically.
B) it implies more cross-sectional area and the fiber can therefore hold more mitochondria, which means it can generate more ATP to power contraction.
C) it has less surface area relative to its volume, so it depolarizes more rapidly, since current has less distance to spread.
D) it has more myofibrils per unit length, which means it can form more
Cross-bridges, and generate more power (force).
E) none of these.

Question 20

Which fibers will have a rich blood supply and a high myoglobin content?

A) slow oxidative fibers (Type I)
B) fast oxidative fibers (Type IIa)
C) fast glycolytic fibers (Type IIx)
D) fast and slow glycolytic fibers
E) fast and slow oxidative fibers

Question 21

In spinal reflex pathways, motor neurons receive inputs from

A) sensory afferents and/or internurons.
B) cortical neurons whose cell bodies reside in the primary motor cortex.
C) cortical neurons whose cell bodies reside in the somatosensory cortex.
D) cerebellar neurons.
E) brain stem neurons.

Question 22

Regarding the proprioceptors concerned with muscles, the ________ gives information about muscle length, whereas the ________ gives information about muscle tension.

A) muscle spindle; Golgi tendon organ
B) Golgi tendon organ; muscle spindle
C) muscle spindle; Golgi apparatus
D) Golgi apparatus; muscle spindle
E) None of these.

Question 23

Golgi tendon organs are

A) regulated by the activity of $\gamma$ motor neurons.
B) activated by sensory input from the muscle spindle.
C) activated by changes in muscle tension.
D) activated by changes in muscle length.
E) activated by input from the muscle receptor organ.

Question 24

Which of the following statements is correct?

A) Gamma motor neuron activity is too weak to affect whole muscle tension.
B) Golgi tendon organs lie within the belly of the muscle.
C) A muscle spindle is a collection of extrafusal fibers.
D) The primary purpose of the stretch reflex is to counteract the unintended contraction of the quadriceps.
E) Each muscle spindle has one efferent and two afferent neurons which are used for reciprocal innvervation.

Question 25

Which of the following characteristics do skeletal muscle and smooth muscle have in common?

A) Calcium is bound by the protein calmodulin prior to formation of cross-bridges.
B) Tropomyosin is removed from the myosin-binding site on actin, permitting formation of cross-bridges
C) Sliding of thick and thin filaments relative to one another depends on a rise in cytosolic calcium.
D) Sliding of thick and thin filaments relative to one another results in shortening of the sarcomeres.
E) All of these.

Question 26

Multiunit smooth muscle is considered neurogenic, which means

A) contraction occurs following a spontaneous depolarization event.
B) contraction is regulated by pacemaker cells lying within the muscle.
C) the muscle is stimulated to contract through direct nervous input.
D) contraction is proportional to the generator potential of the nerve.
E) more than one of these.

Question 27

The stress relaxation response enables hollow organs, like the stomach, to accommodate increases in the volume of its contents. Typically, an upper limit is placed on the volume, however, by

A) reflex contraction initiated in response to stretch.
B) tension due to stretching of the intermediate filaments within the smooth muscle.
C) inelastic connective tissue associated with the smooth muscle of the organ.
D) the number of cross-bridge sites present on the myosin filaments.

Question 28

Which of the following features distinguishes cardiac muscle from skeletal muscle?

A) Cardiac muscle contraction is modified by hormones.
B) Cardiac cells lack T tubules.
C) Only cardiac muscle has slow myosin ATPase activity.
D) In skeletal muscle Ca²⁺ is released from the sarcoplasmic reticulum.
E) Skeletal muscle has thick myosin and thin actin filaments

Question 29

Which of the following statements is NOT true?

A) Smooth muscle can be classified according to the timing and means of increasing cytosolic Ca²⁺.
B) In smooth muscle, C-type Ca²⁺ channels regulate the influx of extracellular Ca^2+.
C) Smooth muscle tone exists because the muscle has a relatively low resting potential.
D) In smooth muscle, Ca2+ binds directly to myosin light chain kinase as opposed to troponin as it does in skeletal muscle.
E) Skeletal, cardiac, and smooth muscle differ in the energy source used for contraction.

Question 30

Which of the following features distinguishes skeletal muscle from smooth muscle?

A) Only smooth muscle contraction is modified by hormones.
B) Only smooth muscle takes up Ca²⁺ from the extracellular fluid.
C) Only skeletal muscle is neurogenic.
D) Only skeletal muscle has a moderately developed sacroplasmic reticulum.
E) Two of these.

Question 31

Varicosities

A) are bulges at the end of certain types of nerve terminal branches
B) can be found on the postganglionic autonomic fibers associated with certain smooth muscle cells
C) contain neurotransmitter
D) all of these
E) none of these.

Question 32

In single unit smooth muscle, tension is increased by

A) increasing the number of individual cells recruited by neurons to contract.
B) increasing the levels of cytoplasmic calcium available to permit cross-bridge formation.
C) increasing the synthesis of contractile units so that more power is attained.
D) doing all of these.
E) doing none of these.

Question 33

Which of the following muscle types has tone in the absence of an external stimulus?

A) skeletal
B) multiunit smooth muscle
C) single-unit smooth muscle
D) cardiac muscle
E) all of these

Question 34

The myosin filaments of a sarcomere are attached to the Z line by an elastic protein.

Question 35

The largest known protein in any organism is called connectin.

Question 36

The cross-bridges aligned with given thin filaments stroke in unison during a
contraction.

Question 37

A single action potential in a skeletal muscle lasts only about 3-5 msec.

Question 38

In skeletal muscle, a single contractile response may last up to 100 times longer than the
action potential that produced it.

Question 39

Arthropod muscles attach to internal ridges of the exoskeleton called apodemes.

Question 40

A tectonic contraction is a summation of individual twitches and therefore has the same
strength.

Question 41

In vivo, muscles are usually positioned at a relaxed length that is approximately 80% of
their optimal length which maximizes contraction strength.

Question 42

Load and velocity are directly related for eccentric contractions.

Question 43

It is known that interconversion of muscle fiber types is possible. Thus, depending on
usage, fast-glycolytic fibers can be converted to slow-glycolytic fibers.

Question 44

Match each sentence with the most appropriate choice:

-Dihydropyridine receptor

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 45

Match each sentence with the most appropriate choice:

-Ryanodine receptor

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 46

Match each sentence with the most appropriate choice:

-Nicotinic acetylcholine receptors

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 47

Match each sentence with the most appropriate choice:

-Cardiac muscle

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 48

Match each sentence with the most appropriate choice:

-Slow-oxidative

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 49

Match each sentence with the most appropriate choice:

-Fast-oxidative

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 50

Match each sentence with the most appropriate choice:

-Fast-glycolytic

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 51

Match each sentence with the most appropriate choice:

-Rigor

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 52

Match each sentence with the most appropriate choice:

-Cross bridges

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 53

Match each sentence with the most appropriate choice:

-H-zone

A) T tubule
B) Lateral sacs
C) Motor endplate
D) Heart
E) Type I
F) Type IIa
G) Type IIx
H) ATP depletion
I) Myosin heads
J) Myosin tails

Question 54

Compare and contrast 8 major characteristics of multiunit and single-unit smooth muscle.

Question 55

Compare and contrast the source and involvement of Ca²⁺ in smooth muscle and skeletal
muscle contraction. In addition, why is it that T tubules are absent in smooth muscle but present in skeletal muscle cells?.

Question 56

Discuss the importance of creatine phosphate in muscle contraction. Where does creatine phosphate come from?

Question 57

Compare and contrast excitation and contraction in neurogenic multiunit smooth muscle cells and myogenic single-unit smooth muscle cells.

Question 58

Explain why muscles evolved for speed.