Chapter 10
Skeletal Muscle
Tissue
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Objectives
• Know the various functions of muscle
• Know the macroscopic and microscopic arrangement
of skeletal muscle
• Understand how muscles attach to bone and what
origin and insertion describe
• Know the types of skeletal muscle fibers
• Know what muscular dystrophy is
Functions and Characteristics
• Produces movement
• Contractility
• Maintains posture
• Excitability
• Joint stability
• Extensibility
• Generates heat
• Elasticity
Muscle Tissue Types
• Skeletal muscle
– Allows for movement
• Smooth muscles
– Found in the walls of hollow vicseral organs
• Cardiac muscles
– Only found within walls of heart
Structure
• Macro to micro
– Epimysium
• Dense irregular CT
– Fascicles
• Wrapped by perimysium
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– Muscle fibers (cells)
• Wrapped by endomysium
– Myofibrils
• Contractile element
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Microanatomy of Myofibril
• Dark band
– A band
• Light band
– I band
• H zone
• Z disc
– Sarcomere
• Titin
– Largest protein in body
– Stabilizes thick fillaments
– Gives muscle elasticity
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The Sarcomere
• Functional unit
• Microfilaments
– Actin
• Troponin
• Tropomyosin
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– Myosin
• Heads contain two
binding sites
• Actin and ATPase
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Innervation of Skeletal Muscle
• Motor neuron and neuromuscular junction
Muscle Contractions
• Concentric
– Contraction that occurs when muscle shortens
and causes a movement
• Eccentric
– Contraction the occurs while muscle lengthens
Muscle Attachments
• Two types of attachments
– Indirect
• Muscles connected to bones via visible tendons
• Tendons merge with periosteum and bony matrix
– Aponeurosis – broad sheet-like tendon
– Direct
• Muscle appears to be directly connected to the bone
with little space between them
– Small microscopic gaps bridged by collagen fibers
– Not always to bone, may be to fascia or the skin
Muscle Attachments
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Origins and Insertions
• Origin – bony site of attachment that remains
more stationary
• Insertion – bony site of attachment that is
more mobile
• Belly – thick portion of muscle between
attachment sites
Types of Muscle Fibers
Slow-oxidative fibers (SO)
• Thin red fibers
Fast-glycolytic fibers (FG)
• Thick white fibers
– Rich in myoglobin
– Little myoglobin
• Rely on aerobic metabolism
• Rely on glycolysis
• Slow twitch: endurance,
long duration contraction
• Fast twitch: strength, short
duration contraction:
Fast-oxidative fibers (FO)
• Intermediate fibers
• Rich in myoglobin
Disorders of Skeletal Muscle
• Muscular Dystrophy
– Inherited disorder
• Dysfunction in the protein dystrophin
– Muscular tissue is replaced by fat and CT