Cardiac Muscle
• Cardiac muscle fibers are small and cylindrical compared to skeletal muscle fibers.
• Nuclei are central, single and oval.
• Muscle fibers are branched.
• Interculated disc one of the unique feature of cardiac muscle is the junction between adjacent cardiac muscle cells.
• It is zig zag in appearance and made up of three types of cell junctions desmosomes, gap junctions and tight junctions. Allows electrical impulse to pass from one cell to another and makes the cardiac muscle fiber a functional syncytium.
• Cardiac muscle is also striated but striations are not prominent under lower magnification,
• Cardiac muscle is involuntary, seen only in heart.
• It is highly vascular and innervated by autonomic nervous system.
Skeletal Muscle
• Each cell is long cylindrical without branching,
• Fibers run parallel to each other.
• Skeletal muscles have transverse striations which are seen as light (1) and dark (A) bands. Hence they are called striated muscles. Striations are not easily seen under low magnification
• Dark and light bands are due to regular arrangement of actin and myosin filaments.
• Center of T band is called Z line. Center of 'N' band is light H zone. Dark Mline is seen in the center of H zone.
• The part of myofibril between two adjacent 2 lines is called sarcomere which is the functional unit of the muscle.
• Aband remains constant during muscle contraction, I and H bands become short
• Skeletal muscle fiber or cell is covered by sarcolemma (cell membrane) and is multinucleated with flattened peripherally positioned nucleus.
• Skeletal muscles are voluntary muscles, innervated by somatic motor nerves.
Smooth Muscle
• Non-striated, involuntary.
• Spindle or fusiform-shaped cells with central oval-elongated nucleus.
• Sarcoplasm contains actin and myosin filaments without an orderly arrangement. Hence only longitudinal striations are seen.
• Found in walls of the digestive tracts, blood vessels, uterus, etc.
• Innervated by parasympathetic and sympathetic nerves.