Question

What are the series of events in the SA nodal cells that directly cause autorhythmic contraction of cardiac muscle cells? Check all that apply.

A. Fast voltage-gated sodium channels open, causing depolarization after threshold has been reached.
B. Slow voltage-gated sodium channels open, causing a slow depolarization to threshold.
C. Fast voltage-gated calcium channels open, causing depolarization after threshold has been reached.
D. Voltage-gated potassium channels open, causing repolarization.

Answer 1

The SA nodal cells cause autorhythmic contraction of cardiac muscle cells by a slow depolarization through sodium channels, a rapid depolarization via calcium channels, and repolarization through potassium channels.

Step-by-step explanation:

The series of events in the SA nodal cells that directly cause autorhythmic contraction of cardiac muscle cells include the following steps:

• Slow voltage-gated sodium channels open, causing a slow depolarization to threshold, known as the prepotential depolarization.
• Fast voltage-gated calcium channels open, causing a more rapid depolarization after threshold has been reached, leading to the action potential.
• Voltage-gated potassium channels open, leading to repolarization as potassium ions leave the cell.

These events repeat cyclically, leading to the autorhythmic contractions of the heart's pacemaker cells without requiring neural stimulation.