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Action Potentials in Cardiac Muscle Cells

How does the control of cardiac muscle differ from the control of skeletal muscle? The control of cardiac muscle is a different ‘problem’ for that posed by smooth or skeletal muscle. Smooth and skeletal muscles do not generally function continuously but only in response to specific needs. Cardiac muscle must function continuously within a fairly narrow range of activity and be able to alter that activity in response to environmental conditions. Some cardiac muscle cells have the ability to continually relax and contract without external stimuli. This rate of contraction is subject to control. Cardiac muscle has three sources of control. The sinoatrial node within the heart acts to self-regulate the heart. In addition both the nervous system and hormones such as adrenalin influence the rate of contraction of cardiac muscle.

View the animation below, then complete the quiz to test your knowledge of the concept.






1In a cardiac muscle cell, the membrane potential increases rapidly...
A)when potassium gates open and potassium diffuses into the cardiac muscle fiber.
B)when potassium gates open and potassium diffuses out of the cardiac muscle fiber.
C)when the sodium gates open and sodium diffuses into the cardiac muscle fiber.
D)when the sodium gates open and sodium diffuses out of the cardiac muscle fiber.
E)when calcium gates open and calcium diffuses into the cardiac muscle fiber.



2In a cardiac muscle cell, the membrane potential begins to decrease...
A)when potassium gates open and potassium diffuses into the cardiac muscle fiber.
B)when potassium gates open and potassium diffuses out of the cardiac muscle fiber.
C)when the sodium gates open and sodium diffuses into the cardiac muscle fiber.
D)when the sodium gates open and sodium diffuses out of the cardiac muscle fiber.
E)when calcium gates open and calcium diffuses into the cardiac muscle fiber.



3In a cardiac muscle cell, the membrane potential decreases rapidly...
A)when potassium gates open and potassium diffuses into the cardiac muscle fiber.
B)when potassium gates open and potassium diffuses out of the cardiac muscle fiber.
C)when the sodium gates open and sodium diffuses into the cardiac muscle fiber.
D)when the sodium gates open and sodium diffuses out of the cardiac muscle fiber.
E)when calcium gates open and calcium diffuses into the cardiac muscle fiber.



4An action potential in a cardiac muscle fiber is identical to an action potential in a skeletal muscle fiber.
A)True
B)False



5During an action potential, the cardiac muscle cell membrane is most permeable to sodium.
A)True
B)False







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