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Cardiac EC Coupling

How are individual cardiac muscle cells controlled? The heart as a whole is controlled by neurons, hormones, and by the sinoatrial node. In addition, unlike other kinds of muscles, there is direct electrical coupling between adjacent cardiac muscle cells. The coupling is accomplished through the interlocking of plasma membranes at specialized regions where there are gap junctions. At the gap junctions, gated channels in the two cells are directly adjacent to one another. In this way an electrical signal can be sent from cell to cell.

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






1Excitation causes...
A)opening of voltage sensitive membrane calcium channels on the sarcoplasmic reticulum.
B)calcium to bind to calcium receptors on the external surface of the sarcoplasmic reticulum.
C)calcium to flow into the cytosol.
D)contraction of the sarcomeres.
E)opening of voltage sensitive membrane calcium channels on the T tubules.



2Which of the following causes opening of the intrinsic calcium channels of the sarcoplasmic reticulum?
A)opening of voltage sensitive membrane calcium channels on the sarcoplasmic reticulum.
B)calcium binds to calcium receptors on the external surface of the sarcoplasmic reticulum.
C)calcium flows into the cytosol.
D)contraction of the sarcomeres.
E)opening of voltage sensitive membrane calcium channels on the T tubules.



3Increased calcium concentrations in the cytosol causes...
A)opening of voltage sensitive membrane calcium channels on the sarcoplasmic reticulum.
B)calcium to bind to calcium receptors on the external surface of the sarcoplasmic reticulum.
C)calcium to flow into the cytosol.
D)contraction of the sarcomeres.
E)opening of voltage sensitive membrane calcium channels on the T tubules.



4Repolarization of the cardiac muscle fiber is termed excitation.
A)True
B)False



5The calcium involved in muscle contraction ultimately comes from the extracellular fluid.
A)True
B)False







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