Normal cardiac muscle is similar to normal skeletal muscle in terms of
A) the duration of the action potentials, which last 250-300 msec.
B) the duration of the resulting contractions.
C) the refractory period, which continues until relaxation is under way.
D) the appearance of calcium among the myofibrils.
E) the appearance of summation of twitches.
D) the appearance of calcium among the myofibrils.
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The sac around the heart is the
A) pleural sac. B) epicardium. C) peritoneum. D) myocardium. E) pericardium.
________ cells enable the immune system to respond more quickly if the same antigen is encountered a second time.
Fill in the blank(s) with the appropriate word(s).
Which of these fluids is not considered an extracellular fluid
a. lymph b. cerebrospinal fluid c. humors of the eye d. all of the above are considered extracellular fluids
Which of the following statements regarding the sliding filament model is false?
A. The A band remains constant in length. B. Actin and myosin do not shorten during contraction. C. The sarcomere shortens. D. Both actin and myosin myofilaments shorten during contraction. E. The I band and H zones become narrower during contraction.