What are the muscle ridges inside the atria?

• A. Pectinate muscles
• B. Trabeculae carne
• C. Chordae tendineae
• D. Papillary muscles

Answer: (A)

Pectinate muscles are the muscle ridges inside the atria. They appear as comb-like bands on the atrial walls, especially prominent in the right atrial appendage, giving the interior a rough texture. These ridges help increase the atrial surface area and contribute to the atrial kick that aids blood flow into the ventricles. The smooth part of the right atrium is separated from the anterior, trabeculated portion by the crista terminalis, which helps organize where the pectinate muscles are located.

In contrast, trabeculae carneae are the similar ridges found in the ventricles, not the atria. Chordae tendineae and papillary muscles are structures of the ventricles that support the valve cusps, preventing them from flipping back into the atria during contraction.