Review Questions

DIRECTIONS: Each of the numbered items or incomplete statements in this section is followed by answers or completions of the statement. Select the ONE lettered answer or completion that is BEST in each case.

1. The endplate potential at the neuromuscular junction is the result of increased postsynaptic membrane permeability to

(A) Sodium first, then potassium

(B) Sodium and potassium simultaneously

(C) Sodium only

(D) Potassium only

2. The endplate potential differs from a muscle action potential in several ways. In which one of the following ways are they similar?

(A) They are both actively propagated down the length of the muscle fiber

(B) They both arise from changes in the permeability to sodium and potassium ions

(C) They are both initiated by the flow of electrical (ionic) current

(D) In both cases, the membrane potential becomes inside-positive

3. If transmission at the neuromuscular junction were blocked by the application of curare, which one of the events listed below would fail to occur when a motor nerve impulse arrived?

(A) Depolarization of the postsynaptic membrane

(B) Depolarization of the presynaptic membrane

(C) Entry of calcium ions into the presynaptic terminal

(D) Presynaptic release of transmitter substance

4. In a certain muscle, it takes 25 msec for a single twitch to develop its peak force in response to a single stimulus. If this muscle were stimulated with two stimuli spaced 15 msec apart, the result would be

(A) A single twitch identical to the one-stimulus twitch

(B) A contraction similar to a single twitch, but of higher amplitude

(C) Two distinct contractions of very short duration

(D) A failure of the muscle to contract at all

5. The factor most important in producing an isometric contraction is

(A) Keeping the muscle from changing its length

(B) Providing a stimulus adequate to activate all motor units

(C) Determining the resting length of the muscle

(D) Stimulating in a tetanic fashion to produce the maximal force

6. If a muscle is arranged so as to lift an afterload equal to one-half its maximal isometric capabilities, the ultimate force it develops is determined by the

(A) Length of the muscle

(B) Size of the afterload

(C) Strength of the stimulation

(D) Number of motor units activated

7. In a series of afterloaded isotonic twitches, as the load is increased, the

(A) Force developed by the muscle increases and the shortening velocity decreases

(B) Force developed by the muscle increases, while the velocity remains the same

(C) Velocity increases to compensate for the increased afterload

(D) Force developed is determined by the velocity of shortening

8. At which point along the isotonic force-velocity curve is the power output maximal?

(A) At the lowest force and highest velocity (Vmax)

(B) At the highest force and lowest velocity (Fmax)

(C) At a force that is about one third of Fmax

(D) At a velocity that is about two thirds of Vmax

9. Consider a load being lifted by a human hand. Because of the mechanical effects of the skeletal lever system, the biceps muscle exerts a force

(A) Less than the load, but shortens at a higher velocity

(B) Equal to the load, and shortens at a velocity equal to the load

(C) Greater than the load, but shortens at a lower velocity

(D) Independent of the load, and shortens at a velocity independent of the load

10.Muscles that are best suited for brief high-intensity exercise would contain which of the following types of fibers?

(A) Mostly glycolytic (white)

(B) Mostly slow-twitch oxidative (red)

(C) A mix of slow twitch (red) and fast twitch (red)

(D) A mix of glycolytic (white) and fast twitch (red)

11. Smooth muscles that are in the walls of hollow organs

(A) Can shorten without developing force

(B) Can develop force isometrically

(C) Have no contractile function, but resist lengthening

(D) Shorten as the volume of the organ increases

12.The relaxation of smooth muscle is associated with a reduction in free intracellular calcium ion concentration. The effect of the reduction is

(A) Reestablishment of the inhibition of the actin-myosin interaction

(B) Deactivation of the enzymatic activity of the individual actin molecules

(C) Decreased phosphorylation of myosin molecules

(D) Reduced contractile interaction by blocking the active sites of the myosin molecules

13. Which statement below most closely describes the role of calcium ions in the control of smooth muscle contraction?

(A) Binding of calcium ions to regulatory proteins on thin filaments removes the inhibition of actin-myosin interaction

(B) Binding of calcium ions to regulatory proteins associated with thick filaments, specifically calmodulin, activates the enzymatic activity of myosin molecules

(C) Calcium ions serve as a direct inhibitor of the interaction of thick and thin filaments

(D) A high concentration of calcium ions in the myofilament space is

(continued)

required to maintain muscle in a relaxed state

14. Compared with skeletal muscle, smooth muscle

(A) Contracts more slowly, but exerts considerably more force

(B) Contracts more rapidly, but exerts considerably less force

(C) Maintains long-duration contractions economically

(D) Exerts considerable force but can do little shortening

15.Compared with that of skeletal muscle, the crossbridge cycle of smooth muscle (A) Is similar, but runs in the reverse direction

(B) Contains the same steps, but some of them are slower

(C) Does not have a step in which actin and myosin are bound together

(D) Can proceed without the consumption of ATP

16.Receptors in the smooth muscle cell membrane

(A) Function only in combination with electrical activation

(B) Cannot function if the cell is relaxed

(C) Play a variety of regulatory roles

(D) Control chemical activation, but do not affect electrical activation

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