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Biology
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36–2 The Muscular System
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Learning Objectives:
What is the main function of the muscular system?
What are the 3 types of muscle?
Describe and identify the 3 types of muscle.
Understand how myosin and actin work within a muscle.
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Learning Objectives:
5. Explain how a muscle contracts. 6. Describe what a tendon is and how it is used. 7. Identify flexor and extensor muscles. 8. Explain why exercise improves our muscular system.
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Muscles
The function of the muscular system is movement.
Muscle makes up more than 40% of your mass.
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Types of Muscle Tissue
Types of Muscle Tissue
What are the three types of muscle tissue?
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Types of Muscle Tissue
There are three different types of muscle tissue:
skeletal
smooth
cardiac
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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.
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Types of Muscle Tissue
Skeletal Muscles:
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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.
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Types of Muscle Tissue
Smooth Muscles:
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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.
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Types of Muscle Tissue
Cardiac Muscle:
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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.
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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.
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Muscle Contraction
Actin
Skeletal muscle
Myosin
Bundle of muscle fibers
Sarcomere
Z line
Skeletal muscles are made up of bundles of muscle fibers, which in turn are composed of myofibrils. Each myofibril contains thin filaments made of actin and thick filaments made of myosin. Muscle fibers are divided into functional units called sarcomeres.
Myofibril
Muscle fiber (cell)
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Muscle Contraction
How do muscles contract?
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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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Muscle Contraction
During muscle contraction, the actin filaments slide over the myosin filaments, decreasing the distance between the Z lines.
During muscle contraction, the actin filaments slide over the myosin filaments, decreasing the distance between the Z lines. 
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Muscle Contraction
Movement of Actin Filament
Actin
Cross-bridge
Binding sites
Myosin
During muscle contraction, the actin filaments slide over the myosin filaments, decreasing the distance between the Z lines. 
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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.
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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.
Powered by ATP. The myosin cross-bridge changes shape and pulls the actin filament toward the center of the sacromere.
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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.
The cross-bridge is broken, the myosin binds to another site on the actin filament, and the cycle begins again.
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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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25. 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.
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26. 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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27. 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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28. 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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29. 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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30. How Muscles and Bones Interact
Opposing Muscles Contract and Relax
By contracting and relaxing, the triceps and biceps in the upper arm enable you to bend or straighten your elbow.
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31. How Muscles and Bones Interact
Opposing Muscles Contract and Relax
By contracting and relaxing, the triceps and biceps in the upper arm enable you to bend or straighten your elbow.
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32. How Muscles and Bones Interact
Antagonistic pairs: Flexors and Extensors
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33. How Muscles and Bones Interact
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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
ligaments.
tendons.
filaments.
bursae.
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36–2
Muscle cells that are large, have many nuclei, and striations are
skeletal muscle cells.
smooth muscle cells.
cardiac muscle cells.
involuntary muscle cells.
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36–2
Muscle that is found in the walls of blood vessels and intestines is
skeletal muscle.
smooth muscle.
cardiac muscle.
striated muscle.
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36–2
The filaments found in skeletal muscle cells are
actin and myosin
myosin and myofibrils
actin and Z lines
actin and sarcomeres
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36–2
The type of muscle found only in the heart is
skeletal muscle.
striated muscle.
cardiac muscle.
smooth muscle.
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43. END OF SECTION