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Muscles
Skeletal Muscle
• Voluntary:
– controlled consciously
• Striations:
– light and dark bands
• Have many nuclei
Smooth Muscles
• Found in organs or blood vessels.
• Involuntary:
– Not under conscious control
• One nucleus
Cardiac Muscle
• Found on the heart.
• One or two nuclei.
• Involuntary control.
Flexor
• Bends the bone at the joint.
• Ex: Bicep
Extensor
• Makes the bone straighten at
the joint.
Muscle Contraction (Microscopic)
• Myofibril:
– Small fibers found within the cells of muscles.
– *Myofibrils are made of two type of filaments.
Actin Filaments
• Thin filaments made of a
protein called actin.
Myosin Filaments
• Thick filaments made of a
protein called myosin.
Muscle Contraction Step #1
• Actin filaments are stimulated to slide over
the myosin filaments.
• ** The heads of the myosin filaments
connect to the actin and pivot. This
causes them to slide.
Muscle Contraction Step #2
• When the actin filaments slide
the length of the sarcomere
becomes shorter.
Muscle Contraction Step #3
• When the sarcomeres
become shorter this causes
each myofibril to become
shorter.
Myofibril
Skeletal
Muscle Cell
Contractile Proteins
Muscle Contraction Step #4
• When each myofibril
becomes shorter it causes
the muscle fibers to become
shorter.
Muscle Contraction Step # 5
• When each muscle fiber
shortens the overall muscle
contracts.
What Stimulates a Muscle?
1. Contractions are coordinated
with your nervous system:
motor neurons.
2. A stimulated neuron will
cause the release of calcium
in the muscle.
3. Calcium causes the
interaction between the
myosin and actin filaments.