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Skeletal Muscle Physiology
Lecture 1
Skeletal Muscle Characteristics and Functions
Characteristics:
• Multinucleated (peripheral
nuclei)
• Striated
• Voluntary
• Covers bony skeleton
• Motor fibers that contract
rapidly/vigorously, tires easily,
exerts great force
Functions:
• Movement
• Posture
• Heat Generation
• Support
• Respiration
• Communication
• Constriction of organs and vessels
• Heart beat
• Excitability, Contractility, Extensibility,
Elasticity
Parts of Skeletal Muscle
• Skeletal Muscle – contains muscle fibers, CT, blood vessels, nerves;
developed from myoblasts
• Muscle fiber – one muscle cell; single cells; multinucleated;
sarcolemma surrounds muscle fiber
• Epimysium – layer of dense CT around skeletal muscle (contains
bundle of muscle fibers called fascicle)
• Perimysium – second layer of collagen CT around fascicles
• Endomysium – thin delicate layer of CT around muscle fiber contained
in a fascicle
Parts of Skeletal Muscle
• Myofibrils – resides inside a muscle fiber; contractile factor; sarcoplasm
surrounds myofibrils
• Myofilament – resides inside a myofibril; Myosin (thick) and Actin (thin)
• Sarcolemma – cell membrane of the muscle fiber
• Sarcoplasm – cytoplasm of a muscle cell; spaces between the myofibrils
that are filled with intracellular fluid; contains K, Mg, P, protein enzymes,
and mitochondria supplying myofibrils with ATP
• Sarcoplasmic Reticulum – inside the sarcoplasm surrounding myofibrils
which controls muscle contraction; consists of sarcomere
• Sequence of Layers: Fascia  Skeletal Muscle  Epimysium  Perimysium
 Endomysium  Fascicles  Muscle Fiber(Endomysium around entire
muscle fiber)  Sarcolemma(cell membrane of muscle fiber)  Myofibril
 Sarcoplasm(cytoplasm between myofibrils)  Myofilament(actin &
myosin)
Inside a Muscle Fiber- Myofibrils
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Thick protein myofilaments - Myosin
Thin protein myofilaments – Actin
Striations are caused by arrangement of thick and thin myofilaments
Sarcomere – Z line/disc to Z line/disc; contractile unit of a myofibril
A band = dark area (thick + thin)
M line = connects central portion of each thick filament to its neighbors; stabilizes
thick filaments
• H zone = lighter region on either side of M line in resting sarcomere; contains only
THICK myofilaments
• I band = light area; thin only
• Titin = an elastic filament that extends from Z disc to the thick filament and
attaches to M line
Myofilaments
• Thick Filaments = myosin
• Rod like tail (axis) that terminates in two globular heads or cross bridges
• Head region site of Myosin ATPase activity (Breaks down ATP, releases energy)
• Thin Filaments = actin
• Helical structure tethered at one end at the Z disc
• G-actin (globular form of actin)
• F-actin (filaments actin formed from g-actin)
• Tropomyosin
• Rod-shaped protein spiraling around actin and prevents attachment of cross-bridges
• Troponin complex
• Complex of polypeptides
• Tropomyosin and Troponin help control actin’s interaction with myosin
during contraction
Links
• Khan Academy: Skeletal Muscle (YouTube)
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Anatomy of Muscle
Actin and Myosin
Tropomyosin and Troponin
Sarcoplasmic Reticulum
• Biology Medicine Animation: Skeletal Muscle (YouTube)
• *To find links to videos- view PowerPoint in presentation mode and click on
hyperlink (title that is underlined) it will open up internet webpage
for viewing