ANATOMY

Detailed explanation-1: -They are called involuntary muscles. Cardiac muscle has branching fibers, one nucleus per cell, striations, and intercalated disks. Its contraction is not under voluntary control.

Detailed explanation-2: -Therefore, intercalated discs are gap junctions that link adjacent cardiac muscles so that electrical impulses can travel between cells and causes to contract almost simultaneously (Severs 1989).

Detailed explanation-3: -Which shape best describes cardiac muscle cells? The answer is b, branched. Cardiac muscle cells have an irregular, branched appearance that are shorter than the longer, cylindrical cells found in skeletal muscle tissue, and different from the fusiform shape of smooth muscle.

Detailed explanation-4: -The myofibrils are formed by repeating sarcomeres, the basic contractile units of cardiac muscle composed of interdigitating thin (actin) and thick (myosin) filaments (see Figure 65-1), that give the muscle its characteristic striated appearance.

Detailed explanation-5: -Cardiac muscle is striated, like skeletal muscle, as the actin and myosin are arranged in sarcomeres, just as in skeletal muscle. However, cardiac muscle is involuntary. Cardiac muscle cells usually have a single (central) nucleus. The cells are often branched, and are tightly connected by specialised junctions.