Page 323 - Atlas of Histology with Functional Correlations

Three muscle types are skeletal muscle, cardiac muscle, and smooth muscle

All muscles show similarities and differences
All muscles are composed of elongated cells called fibers
Muscle cytoplasm is sarcoplasm, and muscle cell membrane is sarcolemma
Muscle fibers contain myofibrils made of contractile proteins actin and

myosin

SKELETAL MUSCLE

Fibers are multinucleated with peripheral nuclei
Multiple nuclei are because of the fusion of mesenchyme myoblasts during
embryonic development
Each muscle fiber is composed of myofibrils and myofilaments

Actin and myosin filaments form distinct cross-striation patterns
Light I bands contain thin actin, and dark A bands contain thick myosin
filaments

Dense Z line bisects I bands; between Z lines is the contractile unit, the
sarcomere
Accessory proteins align and stabilize actin and myosin filaments
Titin protein anchors myosin filaments, and α-actinin binds actin filaments to
Z lines

Titin centers, positions, and acts like a spring between myosin and Z lines
The protein nebulin anchors thin filaments to Z lines and regulates actin
filament length

The protein desmin links myofibrils at Z lines and attaches them to the
sarcolemma
Muscle is surrounded by connective tissue epimysium
Muscle fascicles are surrounded by connective tissue perimysium
Each muscle fiber is surrounded by connective tissue endomysium

Voluntary muscles are under conscious control
Neuromuscular spindles are specialized stretch receptors in almost all
skeletal muscles

Intrafusal fibers and nerve endings are found in spindle capsules
Stretching of muscle produces a stretch reflex and movement to shorten
muscle

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