Deck 14: Skeletal Muscle Physiology: Frogs and Human Subjects

Question 1

When a muscle cell is at rest, there is a charge separation (voltage) across the plasma membrane called .

A) the resting membrane potential
B) depolarization
C) the battery
D) repolarization

Answer 1

A

Question 2

During the _ period in a muscle cell there is no possibility of generating another action potential.

A) relaxation
B) relative refractory
C) contraction
D) absolute refractory

Answer 2

D

Question 3

Place the following events in the correct sequence in which they occur: excitation-contraction coupling, electrical excitation of the muscle cell membrane, sliding of the myofilaments.

A) sliding of the myofilaments, electrical excitation of the muscle cell membrane, excitation-contraction coupling
B) electrical excitation of the muscle cell membrane, excitation-contraction coupling, sliding of the myofilaments
C) electrical excitation of the muscle cell membrane, sliding of the myofilaments, excitation-contraction coupling
D) excitation-contraction coupling, sliding of myofilaments, electrical excitation of the muscle cell membrane

Answer 3

B

Question 4

The rising phase of a muscle twitch represents .

A) the time of relaxation of the muscle fibers
B) the time of shortening of the sarcomeres of the muscle fibers
C) the time between stimulus and active muscle contraction

Question 5

Graded muscle contractions .

A) depend on increasing frequency of nerve action potentials to each motor unit
B) represent increasing amounts of force generated by a muscle
C) depend on activation of more and more motor units
D) all of the above

Question 6

During an action potential in muscle, .

A) both Na+ and K+ diffuse out of the cell
B) Na+ diffuses into the cell, then K+ diffuses out
C) K+ diffuses into the cell, then Na+ diffuses out
D) both Na+ and K+ diffuse into the cell

Question 7

A muscle twitch is _.

A) a twinge that one feels in an isolated muscle
B) a single contraction of skeletal muscle
C) the maximal force a muscle can generate
D) an action potential in a muscle

Question 8

When muscle is stimulated directly to contract, does the rising phase of the twitch begin immediately? If not, why not?

A) No, the rising phase occurs only after a substantial number of muscle fibers have contracted.
B) No, electrical and chemical changes at the muscle membrane must occur before contraction.
C) No, the falling phase of the twitch must occur first.
D) Yes, it does begin immediately.

Question 9

What causes muscle contractions to be graded?

A) increasing stimulus frequency
B) both increasing stimulus strength and increasing stimulus frequency
C) increasing stimulus strength

Question 10

The gradual activation of more and more motor units is called .

A) raw EMG
B) dynagram
C) wave summation
D) recruitment

Question 11

The stimulus from motor neuron to neuromuscular junction is , and the stimulus from axon terminal to muscle sarcolemma is _ .

A) chemical, chemical
B) electrical, chemical
C) chemical, electrical
D) electrical, electrical

Question 12

During this period of muscle twitch, there is no change in tension in the muscle.

A) latent period
B) relaxation period
C) contraction period

Question 13

According to its definition, muscle fatigue is .

A) the physiological inability of a muscle to contract
B) a muscle that begins to "burn" as you exercise
C) a tired muscle
D) an irreversible condition brought about by strong stimulus to a muscle

Question 14

An action potential is .

A) a refractory period of the cell membrane
B) a depolarization of the cell membrane
C) a rapid depolarization and repolarization of the cell membrane that is propagated
D) a repolarization of the cell membrane

Question 15

An electromyogram is .

A) a graphic representation of the voltage waveforms associated with muscle contraction
B) a visual recording of the force generated by muscle contraction
C) an instrument used to record the electrical activity of muscles
D) a device used to measure the force of muscle activity

Question 16

An electromyogram measures .

A) electrical activity of motor neuron
B) electrical activity of muscle
C) tension produced in a muscle

Question 17

From your own experience, predict the relative times to fatigue of a subject's upper limb muscles as they hold a light book or a very heavy book in front of them.

A) The heavy book causes earliest fatigue.
B) The light book causes earliest fatigue.
C) Book weight is unrelated to time of fatigue.
D) It will take hours for either book to cause fatigue.

Question 18

At this stimulus strength, all muscle cells of a particular muscle are being stimulated.

A) maximal stimulus
B) subthreshold stimulus
C) threshold stimulus

Question 19

A motor unit is _ .

A) a period of time during muscle contraction
B) all the axons of nerve cells that innervate a muscle
C) a group of linked muscle cells
D) a single motor neuron and all the muscle cells it innervates

Question 20

In the glycerinated muscle, these substances are necessary for maximal contraction to occur.

A) ATP only
B) ATP, K+, and Mg2+
C) K+ and Mg2+
D) ATP and Ca2+

Question 21

This ion is critical for normal excitation-contraction coupling, but is not necessary for contraction of the glycerinated muscle fibers you worked with in the lab.

A) Mg2+
B) K+
C) Na+
D) Ca2+

Question 22

In your laboratory experiments, you most often observed .

A) both isotonic and isometric contractions
B) isometric contractions
C) neither isotonic nor isometric contractions
D) isotonic contractions

Question 23

Which event requires multiple stimuli?

A) tetanus
B) both muscle twitch and tetanus
C) muscle twitch

Question 24

Most subjects use their dominant forearm far more than their nondominant forearm. How might the dominant forearm differ physiologically or structurally from the nondominant forearm?

A) The muscle fibers may be larger, and contract more efficiently.
B) There may be a great increase in the number of muscle fibers.
C) Psychological factors may result in increased force being generated.

Question 25

Your friend has a paralyzed arm. What physical events might have caused this?

A) damage to the part of the spinal cord that controls that arm
B) drug-induced failure at the neuromuscular junction
C) damage to the part of the brain that controls that arm
D) Any of these events could have caused the paralysis: damage to the part of the brain that controls that arm, damage to the part of the spinal cord that controls that arm, or drug-induced failure at the neuromuscular junction.

Question 26

The maximum force that can be attained by a contracting muscle occurs during .

A) low frequency wave summation
B) a maximal twitch
C) fused tetanus

Question 27

When the nerve to a muscle is destroyed, _.

A) the muscle will no longer contract
B) the muscle will continue to contract normally
C) the muscle will continue to contract weakly
D) the muscle can continue to contract normally or it can continue to contract weakly