Question

The auricular appendages in atrium are ridged by muscular bands called
A. A-Band
B. I-Band
C. Musculi pectinati
D. Columnae carneae

Answer 1

Auricular appendage is a pouch projecting from the top front of each atrium of the heart. It functions as a decompression chamber.

Complete answer:
A. A – Band – Each myofibril has alternate dark and light bands on it. Striated appearance in myofibril is due to the distribution pattern of two important proteins i.e. Actin and myosin. Muscle is composed of elongated cells called muscle fibres. Each muscle fibre is lined by membrane called sarcolemma enclosing sarcoplasm. In sarcoplasm, large numbers of parallel arranged filaments are present called filaments of myofibrils. Each myofibrils has alternate dark and light bands. The dark bands contain myosin called A-bands or anisotropic bond. Myosin filaments are thick filaments.
B. I – Band – The light bands are called I-bands or isotropic bonds, they contain action. They are thin filaments.
C. Musculi pectinati: The auricular appendages in atrium are ridged by a muscular band known as musculi pectinati. Musculi pectinati are parallel ridges present in the walls of the atrium of the heart. The atrial infolding increases the surface area of the atrial chamber at times of dilation.
D. Columnae carneae – These are irregular muscular columns which project from the inner surface of right and left ventricles of the heart. They help to maintain cardiac performance in both healthy and failing hearts by increasing contractility and stroke work.

The correct option is (C) Musculi pectinati.

Note: The pectinate muscles (musculi pectinati) are parallel ridges in the wall of the atria of the heart. They are so called because of their resemblance to the teeth of a comb. Pectinate muscles make up the part of the wall in front of this, the right atrial appendage.