Multiple choice

In cardiac muscles, which of the following events takes place?

  1. The force of contraction is enhanced by propogating epinephrine.

  2. Cardiac muscle contracts in reaction to action potentials generated in the autonomic nerve fibers.

  3. The action potential of cardiac muscle has the similar duration as that of skeletal muscle in the body.

  4. All of Ca2+ needed for contraction of cardiac muscles comes in a myocyte during the plateau phase of the action potential.
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Explanation

Epinephrine is a catecholamine hormone secreted by adrenal medulla. It is a potent stimulator of the sympathetic nervous system stimulating the heart muscle, accelerating the heart rate and increasing cardiac output. In a cardiac muscle, the force of contraction is enhanced by propogating epinephrine.

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