Chapter 5: The Muscular System Section 2
Lesson 5.2
Skeletal Muscle Actions
Skeletal Muscle
• the motor unit
• skeletal fiber types
• muscular strength, power, and endurance
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The Motor Unit
• group of muscle fibers under the control of one
motor neuron
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Generating Action Potentials
• acetylcholine crosses the synaptic cleft at the
neuromuscular junction
• depolarization takes place on muscle fiber
• action potential begins
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Contraction of the Sarcomeres
• sarcomeres shorten by actin
filaments sliding along myosin
filaments – INCLUDE THESE 2
LABELED DRAWINGS IN
YOUR NOTES!

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Maximum Tension and Return to
Relaxation
• action potential always causes entire motor unit
muscle fibers to contract
• all-or-none law
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Review and Assessment
True or False?
1. An action potential causes one half of the fibers in
the motor unit to contract.
2. Acetylcholine crosses the synaptic cleft at the
neuromuscular junction.
3. The sarcomeres lengthen by myosin filaments
sliding over actin filaments.
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Skeletal Muscle Fiber Types
• slow-twitch
• fast-twitch
– type IIa – intermediate between slow and fast
– type IIb – fastest (1/7 the time of slow twitch)
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Skeletal Muscle Fiber Architecture
• parallel fiber arrangements
– fusiform
– bundled
– triangular
• pennate fiber arrangements
– unipennate
– bipennate
– multipennate
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Muscular Strength
• rotary force that muscles can produce at a joint
– the maximum weight you can lift is a measurement of
muscular strength
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Muscle Power
• force x velocity
– how fast you can sprint is a measurement of muscle
power
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Muscle Endurance
• muscle tension/time
– how far you can run is a measurement of muscle
endurance
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Review and Assessment
Match these words with 1–5 below: muscle
endurance, muscular strength, muscle power,
Type I, Type IIb.
1. force x velocity
2. muscle tension/time
3. rotary force that muscles can produce at a joint
4. slow twitch, slow fatigue
5. fast twitch, fast fatigue
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