What is the primary role of the pectinate muscles in the heart?

The pectinate muscles play a significant role in the atria of the heart, specifically enhancing the efficiency of atrial contraction. These parallel ridges of muscle fibers are located primarily in the right atrium and, to a lesser extent, in the left atrium. Their arrangement increases the surface area of the atrial walls and adds to the strength of the muscular contraction during atrial systole. This increased contractile efficiency helps to draw blood into the ventricles more effectively when the atria contract, thereby contributing to overall cardiac efficiency.

While structural support for valves, ventricular contraction, and heart rate regulation are essential functions of the heart, they are not directly related to the specialized role of pectinate muscles. Structural support is primarily provided by the connective tissue and annulus fibrosus surrounding the valves, the ventricles' contraction is facilitated by different muscle structures (mainly the myocardium of the ventricles), and heart rate is regulated by the sinoatrial node and autonomic nervous system rather than the pectinate muscles themselves. Therefore, the primary function of the pectinate muscles is indeed to assist in atrial contraction.