Skeletal Muscle

• Usually attached to bones
• Voluntary
• Striated (filaments in bands)
• Multinucleated

Cardiac Muscle

• Wall of heart
• Involuntary
• Striated and branched (intercalated disks)
• Single nucleus

Smooth Muscle

• Walls of most viscera, blood vessels and skin
• Involuntary
• Not striated
• One centrally located nucleus

Compared to skeletal muscle fibers, smooth muscle fibers are:

• Shorter
• Single, centrally located nucleus
• Elongated with tapering ends

Visceral Smooth Muscle

• Single-unit smooth muscle
• Sheets of muscle fibers
• Fibers held together by gap junctions
• Exhibit rhythmicity
• Exhibit peristalsis
• Walls of most hollow organs

Multi-unit Smooth Muscle

• Less organized
• Function as separate units (Fibers function separately)

• Iris of eye
• Walls of blood vessels

Cardiac Muscle

• Located only in the heart
• Muscle fibers joined together by intercalated discs
• Fibers branch
• Network of fibers contracts as a unit
• Self-exciting and rhythmic
• Longer refractory period than skeletal muscle

Tissues of the muscular system:

• Skeletal muscle tissue
• Nervous tissue
• Blood
• Connective tissues

Types of dense, white, fibrous connective tissue found in skeletal muscles throughout body:

• Fascia—layered; covers all muscles
• Tendons—cordlike; connects muscle to bone
• Aponeuroses—sheetlike; connects muscle to muscle

Connective tissues found covering individual muscles:

• Epimysium
• Perimysium
• Endomysium

Muscle Structure:

• Fascicles
• Muscle fiber (muscle cell)
• Myofibrils
• Thin and thick myofilaments
• Actin (thin) and myosin (thick) proteins

Parts of a sarcomere:

• I band (actin-thin)
• A band (myosin-thick and actin-thin)
• H zone (myosin-thick)
• Z line (actin disc)
• M line (myosin)

Thick myofilaments

• Composed of myosin protein
• Form the cross-bridges

Thin myofilaments

• Composed of actin protein
• Associated with troponin and tropomyosin proteins