Transcript Mechanics of Movement II: Making joints move

Mechanics of Movement II:
Muscle Action Across Joints
Review
muscle force generation
Muscle Physics
--force versus cross section
--length versus strain
Lever mechanics
Stabilizing the joint—isometric and eccentric
contraction
Frolich, Human Anatomy, Mechanics of Movement
Muscle Structure Review


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
Muscle fiber = muscle cell
Fibers lined up = direction of pull
Tendon attaches to bone
Muscle pulls on bone
Fig. 10.1
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Muscle Origin
and Insertion

Origin
 Proximal
 Fixed
 Insertion
 Distal
 Moves
 (usually!!)
Fig. 10.3
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Mechanics of Contraction

Muscle cell is unit
 Role of actin/myosin
 Action potential or
depolarization of
membrane makes cell
“contract”
 (motor neuron action
potential stimulates
muscle membrane
depolarization)
Fig. 10.4
Frolich, Human Anatomy, Mechanics of Movement
Visualizing muscle contraction
How actinmyosin
complex
(sarcomere)
shorten muscle
Fig. 10.7
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Summary of Muscle Organization/Function
Frolich, Human Anatomy, Mechanics of Movement
Summary of Muscle Organization/Function
Frolich, Human Anatomy, Mechanics of Movement
Summary of Muscle Organization/Function
Frolich, Human Anatomy, Mechanics of Movement
Levels of Muscle
Organization
Table 10.2
Frolich, Human Anatomy, Mechanics of Movement
Muscle Physics: Principle I

Cross sectional area is proportional
to Force of muscle
Frolich, Human Anatomy, Mechanics of Movement
Muscle Physics: Principle II

Length of muscle is proportional to
ability to shorten (strain)
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Short, fat muscles
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
Number of sarcomeres in series gives
shortening ability
Lots of force
Less shortening range
Long, skinny muscles


Less force
More shortening range
Frolich, Human Anatomy, Mechanics of Movement
Muscle Physics: Principle III

Force generation depends
on current length of
muscle or overlap in
actin/myosin of
sarcomeres
 Muscle force strongest
between 80-120% of
normal resting length—
WHY? (don’t forget role of cross-bridges)
 Most muscles arranged to
work in this range
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Types of fascicle arrangements

Affects length and
cross section of
muscle
 Thus affects force
and shortening
properties of muscle
 See Muscle Physics
Principles I-III if this
doesn’t make sense
Fig. 11.3
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Muscle movement across joints
is like lever system
Fig. 11.1
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First-class lever
Fig. 11.2
Frolich, Human Anatomy, Mechanics of Movement
Second-class lever
Fig. 11.2
Frolich, Human Anatomy, Mechanics of Movement
Third-class lever
Fig. 11.2
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Stabilization and Control Around Joint
Agonist
Main Mover
E.g. biceps
Antagonist
Opposite
motion
E.g. triceps
Synergist
Aids agonist
E.g. brachialis


Antagonist often “fires” or contracts or is stimulated
simultaneously with agonist to stabilize around joint
during movement
NOTE: Muscle “contraction” or stimulus to “fire”
does not always result in muscle shortening
Frolich, Human Anatomy, Mechanics of Movement
Agonist/Antagonist
Frolich, Human Anatomy, Mechanics of Movement
Relation between muscle contraction
(or “firing”) and shortening
 Concentric
contraction—muscle contracts and
shortens to cause movement across joint
 Isometric contraction—muscle contracts but
stays same length to hold joint or body in
same position
 Eccentric contraction—muscle contracts while
lengthening to stabilize joint during movement
(most common in antagonist to slow
movement caused by agonist)
Frolich, Human Anatomy, Mechanics of Movement