What triggers the contraction of heart muscle cells?

The contraction of heart muscle cells, known as cardiomyocytes, is primarily triggered by electrical impulses generated by action potentials. When the heart is stimulated, specialized cells within the sinoatrial (SA) node generate electrical signals that spread throughout the heart muscle. This wave of depolarization causes the muscle cells to contract.

Action potentials lead to a change in the membrane potential of cardiomyocytes, which opens voltage-gated calcium channels in the cell membrane. This influx of calcium ions plays a critical role in the contraction process, as calcium binds to proteins within the muscle cells to facilitate contraction through the sliding filament mechanism. The organized and rhythmic nature of these electrical impulses ensures that the heart contracts in a coordinated manner, crucial for effective pumping of blood.

While other factors, such as hormones and pressure changes, can influence heart function, they do not directly trigger the contraction of heart muscle cells in the same manner as electrical impulses. Hormones can modulate heart rate and strength of contractions, but the fundamental trigger for the actual contraction is the action potential-driven electrical impulses.