THE MUSCULAR SYSTEM Function: locomotion Types of muscles in vertebrates •Involuntary (Smooth)- associated with viscera; no striations •Voluntary (striated) skeletal muscles; under conscious control •Involuntary striated cardiac muscles- found in the heart
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THE MUSCULAR SYSTEM
Function: locomotion
Types of muscles in vertebrates •Involuntary (Smooth)- associated with viscera; no striations
•Voluntary (striated) skeletal muscles; under conscious control
•Involuntary striated cardiac muscles- found in the heart
• Tendons– Straps of densely connective tissue attaching muscles to
bones
• Muscles in movable joints of vertebrates are attached in opposing pairs:– Flexors and Extensors
MUSCLE ORGANIZATION
A CLOSER LOOK AT THE MUSCLE FIBER
MYOSINACTIN
Z Line
H ZoneI Band
THE MYOFIBRIL
Muscular Contraction- THE SLIDING FILAMENT THEORY
•Thin filaments slide across the thick filaments to pull the Z lines together and shorten the sarcomere •I Bands shorten and H zone disappears •sarcomeres in myofibril shorten, they are pulled toward the center of the myofibril and the muscle to contract to about half of its resting length
How Muscles Work
• When myosin filaments contract heads of myosin filaments move first, moving them closer in the direction of the flex.
• Role of Calcium Ions in Contraction– When muscle is relaxed, attachment sites for
myosin heads are physically blocked by tropomyosin.
• In order to contract a muscle, troponin must move tropomyosin.
– Complex regulated calcium ion concentration.
» Muscle fibers store Ca++ in sarcoplasmic reticulum.
HUMAN MUSCULAR SYSTEM
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