Cardiac Muscle Contraction and Regulation Quiz

Cardiac Muscle Characteristics

• Cardiac muscle cannot increase motor unit recruitment or undergo tetanic contraction due to the absence of motor units and the inability to voluntarily recruit more fibers.
• The lack of tetanic contraction in cardiac muscle is attributed to the asynchronous activation of cardiac myocytes, preventing force summation during cardiac twitches.

Cardiac Muscle Contraction

• The primary mechanism by which cardiac muscle cells modify the strength of contraction is through changes in intracellular Ca++ concentrations.
• Dihydropyridine (DHP) Ca++ channels are triggered to open by depolarization of the cardiac muscle cell membrane.
• The main role of DHP channels in cardiac muscle cells is to regulate the influx of Ca++ ions, which triggers contraction.

Cardiac Muscle Function

• SERCA2 (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase 2) is responsible for reuptaking Ca++ ions into the sarcoplasmic reticulum, reducing intracellular Ca++ concentrations and allowing for muscle relaxation.

Cardiac Cycle

• During the late rapid ejection phase, ~70% of stroke volume gets ejected from the left ventricle.
• The primary role of the atria in the cardiac cycle is to serve as a primer pump, allowing for the efficient filling of the ventricles.

Calcium Regulation

• Mucopolysaccharides sequester Ca++ ions, making them ready for release during action potentials.
• The release of Ca++ from the sarcoplasmic reticulum (SR) in cardiac muscle cells is triggered by the opening of ryanodine receptors.

Test your knowledge of the contraction of cardiac muscle, events during the cardiac cycle, and the regulation of cardiac output with this quiz. Explore the mechanisms of matching cardiac output to metabolic tissue demands and the unique aspects of heart rate and contractile force.