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Biology
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36–2 The Muscular System
36–2 The Muscular System
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The function of the muscular system is movement.
More than 40% of the mass of the average human body is muscle.
36–2 The Muscular System
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Types of Muscle Tissue
Types of Muscle Tissue
What are the three types of muscle tissue?
36–2 The Muscular System
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Types of Muscle Tissue
There are three different types of muscle tissue: • skeletal • smooth • cardiac
36–2 The Muscular System
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Types of Muscle Tissue
Skeletal Muscles
Skeletal muscles:
• are usually attached to bones.
• are responsible for voluntary movements.
• have many nuclei.
• are sometimes called striated muscles.
36–2 The Muscular System
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Types of Muscle Tissue
Smooth Muscles
Smooth muscles:
• are usually not under voluntary control.
• are spindle-shaped.
• have one nucleus.
• are not striated.
• are found in many internal organs and blood vessels.
36–2 The Muscular System
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Types of Muscle Tissue
Most smooth muscle cells can function without nervous stimulation.
They are connected by gap junctions that allow electrical impulses to travel among muscle cells.
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Types of Muscle Tissue
Cardiac Muscle
Cardiac muscle:
• is only found in the heart.
• is striated.
• may have one or two nuclei.
Cardiac muscle cells are connected to each other by gap junctions.
36–2 The Muscular System
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Muscle Contraction
Muscle Contraction
The fibers in skeletal muscles are composed of smaller structures called myofibrils.
Each myofibril has smaller structures called filaments.
The thick filaments contain a protein called myosin.
The thin filaments contain a protein called actin.
36–2 The Muscular System
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Muscle Contraction
Filaments are arranged along the muscle fiber in units called sarcomeres.
Sarcomeres are separated by regions called Z lines.
When a muscle is relaxed, there are no thin filaments in the center of a sarcomere.
36–2 The Muscular System
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Muscle Contraction
Skeletal muscle
Bundle of muscle fibers
Muscle fiber (cell)
Myofibril
Z line
Sarcomere
Myosin
Actin
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Muscle Contraction
How do muscles contract?
36–2 The Muscular System
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Muscle Contraction
A muscle contracts when the thin filaments in the muscle fiber slide over the thick filaments.
This process is called the sliding filament model of muscle contraction.
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36–2 The Muscular System
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Muscle Contraction
During muscle contraction, the actin filaments slide over the myosin filaments, decreasing the distance between the Z lines.
36–2 The Muscular System
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Muscle Contraction
Binding sites Myosin
Cross-bridge
Actin
Movement of Actin Filament
36–2 The Muscular System
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Muscle Contraction
During muscle contraction, the head of a myosin filament attaches to a binding site on actin, forming a cross-bridge.
36–2 The Muscular System
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Muscle Contraction
Powered by ATP, the myosin cross-bridge changes shape and pulls the actin filament toward the center of the sarcomere.
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Muscle Contraction
The cross-bridge is broken, the myosin binds to another site on the actin filament, and the cycle begins again.
36–2 The Muscular System
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Muscle Contraction
When many myosin cross-bridges change shape in a fraction of a second, the muscle fiber shortens with considerable force.
The energy for muscle contraction is supplied by ATP.
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Control of Muscle Contraction
Control of Muscle Contraction
Impulses from motor neurons control the contraction of skeletal muscle fibers.
A neuromuscular junction is the point of contact between a motor neuron and a skeletal muscle cell.
36–2 The Muscular System
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Control of Muscle Contraction
Vesicles in the axon terminals of the motor neuron release a neurotransmitter called acetylcholine.
Acetylcholine produce an impulse in the cell membrane of the muscle fiber.
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Control of Muscle Contraction
The impulse causes the release of calcium ions within the fiber.
The calcium ions affect regulatory proteins that allow actin and myosin filaments to interact.
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Control of Muscle Contraction
A muscle cell remains contracted until the release of acetylcholine stops and an enzyme produced at the axon terminal destroys any remaining acetylcholine.
Then, the cell pumps calcium ions back into storage, the cross-bridges stop forming, and contraction ends.
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How Muscles and Bones Interact
How Muscles and Bones Interact
Skeletal muscles are joined to bones by tendons.
Tendons pull on the bones so they work like levers.
The joint functions as a fulcrum.
The muscles provide the force to move the lever.
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How Muscles and Bones Interact
Opposing Muscles Contract and Relax
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How Muscles and Bones Interact
Opposing Muscles Contract and Relax
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How Muscles and Bones Interact
A controlled movement requires contraction by both muscles.
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Exercise and Health
Exercise and Health
Why is exercise important?
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Exercise and Health
Regular exercise is important in maintaining muscular strength and flexibility.
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Exercise and Health
Aerobic exercises help the body’s systems to become more efficient.
Resistance exercises increase muscle size and strength.
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36–2
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36–2
Skeletal muscles are joined to bones by tough connective tissue called
a. ligaments.
b. tendons.
c. filaments.
d. bursae.
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36–2
Muscle cells that are large, have many nuclei, and striations are
a. skeletal muscle cells.
b. smooth muscle cells.
c. cardiac muscle cells.
d. involuntary muscle cells.
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36–2
Muscle that is found in the walls of blood vessels and intestines is
a. skeletal muscle.
b. smooth muscle.
c. cardiac muscle.
d. striated muscle.
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36–2
The filaments found in skeletal muscle cells are
a. actin and myosin.
b. myosin and myofibrils.
c. actin and Z lines.
d. actin and sarcomeres.
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36–2
The type of muscle found only in the heart is
a. skeletal muscle.
b. striated muscle.
c. cardiac muscle.
d. smooth muscle.
END OF SECTION