Muscle tissues

Cardiac striated muscle tissue

• is organ-specific: the heart (ventricles and atria), orifices of the venae cavae
• cardiac muscle cells are structural units of the tissue

Cardiac muscle cells

• are classified into contractile (typical, functional), conducting (atypical), and secretory cells
• contractile cardiac muscle cells (the most common):
• cylindrical or branching cells bound to one another by intercalated discs (cell boundaries). They form a uniform network of functional muscle "fibers" with an ability to produce strong, rapid, rhythmic, involuntary contractions
• they are covered by the sarcolemma. There are one or two nuclei in the center of such a cell. There are also striated myofibrils, the endoplasmic (sarcoplasmic) reticulum, numerous mitochondria, lysosomes, lipid and glycogen inclusions
• conducting cardiac muscle cells are not so rich in myofibrils compared to the contractile cells. They are intended to generate nerve impulses and to conduct excitation to the typical muscle cells
• secretory cardiac muscle cells are intended to produce humoral factors regulating the circulating blood volume and vascular wall tone

Ventricular muscle tissue

Structure of contractile cardiac muscle cells

Conducting and contractile cardiac muscle cells

Endocrine cardiac myocytes

Contractile apparatus and conduction of excitation in striated muscle tissues

The contractile apparatus is represented by striated myofibrils

• sarcomeres are structural units of myofibrils. These are systems of thin actin and thick myosin filaments that are arranged by a supporting machinery of myofibrils

The apparatus of excitation conduction (sarcotubular system) is a complex of tubular membrane structures to enable propagation of depolarization wave via the sarcolemma to all the myofibrils

Structure of striated myofibril

Conduction of excitation