Which statement best defines autorhythmicity in cardiac tissue?

Which statement best defines autorhythmicity in cardiac tissue?

• A. The ability of nodal cells to depolarize and fire an action potential spontaneously
• B. The ability to contract in a coordinated rhythm
• C. The ability to respond to external nerves to trigger contraction
• D. The ability to repolarize without any stimulus

Answer: (A)

Autorhythmicity is the heart’s own built-in ability to generate electrical impulses without external input. Certain cardiac cells, the nodal or pacemaker cells (notably in the SA node), have an unstable resting potential that slowly depolarizes—a pacemaker potential—until it reaches threshold and triggers an action potential. This spontaneous firing sets the heart’s rhythm and initiates the conduction wave that coordinates contraction. The autonomic nervous system can modulate how fast or slow this intrinsic rhythm runs, but the impulse generation itself is inherent to these pacemaker cells. The other ideas describe contraction in general, modulation by nerves, or a phase of the action potential, but they don’t define the intrinsic, automatic generation of impulses that autorhythmicity refers to.

Autorhythmicity is the heart’s own built-in ability to generate electrical impulses without external input. Certain cardiac cells, the nodal or pacemaker cells (notably in the SA node), have an unstable resting potential that slowly depolarizes—a pacemaker potential—until it reaches threshold and triggers an action potential. This spontaneous firing sets the heart’s rhythm and initiates the conduction wave that coordinates contraction. The autonomic nervous system can modulate how fast or slow this intrinsic rhythm runs, but the impulse generation itself is inherent to these pacemaker cells. The other ideas describe contraction in general, modulation by nerves, or a phase of the action potential, but they don’t define the intrinsic, automatic generation of impulses that autorhythmicity refers to.