Download How muscles contract

Muscle Teamwork

Agonist (prime mover):
- the muscle or group of muscles producing a desired effect
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Antagonist:
- the muscle or group of muscles opposing the action
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Synergist:
- the muscles surrounding the joint being moved
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Fixators:
- the muscle or group of muscles that steady joints closer to the body axis so
that the desired action can occur
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Bending or straightening of elbow requires the coordinated
interplay of the biceps and triceps muscles
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Contractile Machinery:
Sarcomeres
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Contractile units
Organized in series ( attached
end to end)
Two types of protein
myofilaments:
- Actin:
thin filament
- Myosin: thick filament
Each myosin is surrounded by
six actin filaments
Projecting from each myosin
are tiny contractile myosin
bridges
Longitudinal section of myofibril
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(a) At rest
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High microscope magnification of sarcomeres
within a myofibril
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Contractile Machinery:
Crossbridge formation and movement
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Cross bridge movement:
- similar to the stroking of the oars and
 Cross bridge formation:
movement of rowing shell
- a signal comes from the motor
- movement of myosin filaments in relation
nerve activating the fibre
- the heads of the myosin filaments to actin filaments
- shortening of the sarcomere
temporarily attach themselves to
- shortening of each sarcomere is additive
the actin filaments
Longitudinal section of myofibril
b) Contraction
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Contractile Machinery:
Optimal Crossbridge formation
Longitudinal section of myofibril
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Sarcomeres should be optimal
distance apart
For muscle contraction: optimal
distance is (0.0019-0.0022 mm)
At this distance an optimal number
of cross bridges is formed
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If the sarcomeres are stretched
farther apart than optimal distance:
- fewer cross bridges can form 
less force produced

If the sarcomeres are too close
together:
- cross bridges interfere with one
another as they form  less force
produced
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c) Powerful stretching
d) Powerful contraction
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Contractile Machinery:
Optimal muscle length and optimal joint angle
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The distance between sarcomeres is dependent on the stretch of
the muscle and the position of the joint
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Maximal muscle force occurs at optimal muscle length (lo)
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Maximal muscle force occurs at optimal joint angle
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Optimal joint angle occurs at optimal muscle length
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Muscle tension during elbow flexion at constant speed
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Contractile Machinery:
Tendons, origin, insertion
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In order for muscles to contract, they must be
attached to the bones to create movement
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Tendons: strong fibrous tissues at the ends of
each muscle that attach muscle to bone
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Origin:
the end of the muscle attached to the
bone that does not move
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Insertion: the point of attachment of the muscle
on the bone that moves
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