31) After death, rigor mortis lasts until

A) ATP is produced.

B) T-tubules recapture calcium ions.

C) sodium ions are released by the sarcoplasmic reticulum.

D) sarcomeres lengthen.

E) myofilaments are broken down.

32) Botulism

A) is the result of an attack on acetylcholine receptors by the immune system.

B) is usually tied to a genetic predisposition.

C) is a viral illness.

D) results from the loss of acetylcholine receptors at the motor end plate.

E) results from a bacterial toxin that prevents the release of acetylcholine at the axon terminals.

33) Which of the following occurs when tension production rises to a peak and very brief periods of relaxation occur?

A) resting period

B) latency

C) tension plateau

D) incomplete tetanus

E) complete tetanus

34) A single stimulus-contraction-relaxation sequence in a muscle fiber is known as a(n) ________.

A) incomplete tetanus

B) latent period

C) complete tetanus

D) summation

E) twitch

35) Calcium ions are released from the sarcoplasmic reticulum during the ________ phase of contraction.

A) latent

B) contraction

C) twitch

D) relaxation

E) recovery

36) Which of the following occurs as a result of motor units in a particular muscle being always active, even though their contractions do not produce enough movement to cause contraction?

A) treppe

B) tetany

C) muscle tone

D) fatigue

E) a twitch

37) Which statement regarding the relaxation phase of a muscle twitch is true?

A) The phase begins at stimulation and typically lasts about two milliseconds.

B) Muscle tension falls to resting levels.

C) The action potential sweeps across the sarcomere during this period.

D) Tension rises to a peak.

E) Cross-bridges are interacting with active sites on actin filaments throughout this period.

38) During which phase is the stimulus frequency so high that the relaxation phase is eliminated?

A) complete tetanus

B) a twitch

C) incomplete tetanus

D) recovery

E) recruitment

39) Regarding muscle fiber elongation,

A) many active mechanisms exist for muscle fiber elongation.

B) muscle contraction is passive; whereas, elongation is active.

C) opposing muscle movements are not a factor.

D) gravity may help lengthen a muscle fiber after elongation.

E) elastic forces are generated where a muscle fiber elongates.

40) Choose the correct statement regarding motor units.

A) Muscle fibers of each motor unit are not mingled with those of other motor units.

B) During a sustained contraction, all motor units are activated simultaneously.

C) A motor neuron may control two or three muscle fibers of the eye.

D) When muscles contract for sustained periods, maximal tension is maintained.

E) Most motor neurons control fewer than five muscle fibers.