What does autorhythmicity refer to in cardiac muscle?

What does autorhythmicity refer to in cardiac muscle?

• A. Cardiac muscles require external stimulus to depolarize.
• B. Nodal cells spontaneously depolarize to initiate action potentials.
• C. Muscle cells contract without any electrical signals.
• D. The heart's conduction system slows conduction at nodes.

Answer: (B)

Autorhythmicity refers to the heart having pacemaker cells that generate impulses on their own, without needing a neural signal. Nod-like pacemaker cells, especially in the SA node, undergo a slow, automatic depolarization (pacemaker potential) due to specialized ion channels, so they reach threshold and fire an action potential spontaneously. This impulse then spreads through the heart’s conduction system to coordinate the heartbeat, setting the pace of the whole organ. External stimulation isn’t required for these cells to fire, and contractile muscle cells rely on those impulses to contract—so they don’t depolarize spontaneously. The idea that conduction simply slows at the nodes describes a normal feature of signal timing, not the origin of automatic Pacemaker activity.

Autorhythmicity refers to the heart having pacemaker cells that generate impulses on their own, without needing a neural signal. Nod-like pacemaker cells, especially in the SA node, undergo a slow, automatic depolarization (pacemaker potential) due to specialized ion channels, so they reach threshold and fire an action potential spontaneously. This impulse then spreads through the heart’s conduction system to coordinate the heartbeat, setting the pace of the whole organ. External stimulation isn’t required for these cells to fire, and contractile muscle cells rely on those impulses to contract—so they don’t depolarize spontaneously. The idea that conduction simply slows at the nodes describes a normal feature of signal timing, not the origin of automatic Pacemaker activity.