Transcript The Muscular System Manual: The Skeletal Muscles of the

Tarrant County College District Massage Therapy Program
South Campus
Slides from Joe Muscolino, Kinesiology
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1
 Describe
how a muscle can have a partial
contraction, and explain the meaning of
the Henneman size principle.
 Explain the difference between the
intrinsic strength of a muscle and the
extrinsic strength of a muscle.
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2
 Describe
the various types of muscle
fiber architecture, and explain the
advantages/disadvantages of
longitudinal versus pennate muscles.
 Describe active tension and passive
tension of a muscle.
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3
 Hierarchy
of motor unit recruitment:
• Weak contraction = small motor unit
• Stronger = increasingly large motor units in
addition to smaller motor units
 Hierarchy
known as the Henneman size
principle
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 If
every motor unit of a muscle contracts,
the muscle contracts at 100% of its
strength.
 If only some motor units contract, the
muscle will have a partial contraction.
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5
 Longitudinal
muscles: fibers run
longitudinally
 Categories of longitudinal muscle
• Fusiform (spindle)
• Strap
• Rectangular
• Rhomboidal
• Triangular (fan-shaped)
• Sphincter
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Figure 14-1
From Muscolino JE: The muscular system manual: the skeletal muscles of the human
body, ed 3, St Louis, 2010, Mosby
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Figure 14-1
From Muscolino JE: The muscular system manual: the skeletal muscles of the human
body, ed 3, St Louis, 2010, Mosby
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8
 Pennate
muscles: fibers arranged in a
featherlike manner
 Types of pennate muscle
• Unipennate muscle
• Bipennate muscle
• Multipennate muscle
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Figure 14-2
From Muscolino JE: The muscular system manual: the skeletal muscles of the human
body, ed 3, St Louis, 2010, Mosby
Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.
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10
 Longitudinal
muscles: long muscle fibers
 Pennate muscles: short muscle fibers
• But pennate muscles have more muscle fibers
 Fibers
of longitudinal muscles oriented
along length of muscle
 Fibers of pennate muscles oriented at
oblique angles to the length of the
muscle
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 Active
tension: generated by sliding
filament mechanism (i.e., its contraction)
 Passive tension: created by fascia of the
muscle
 Total tension: active and passive tension
combined
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 Explain
the relationship between the
sliding filament mechanism and
shortened active insufficiency and
lengthened active insufficiency.
 Give an example of shortened active
insufficiency and lengthened active
insufficiency.
 Interpret the length-tension relationship
curve for active tension, passive tension,
and total tension of a muscle.
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 Explain
the meaning of the active,
passive, and total tension curves of the
length-tension relationship curve.
 Describe the relationship between the
concepts of the sliding filament
mechanism, active length-tension
relationship curve, and active
insufficiency.
 Define the terms internal force and
external force and give an example of
each.
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 Explain
the relationship between
leverage and the extrinsic strength of a
muscle.
 Describe the advantage and
disadvantage of a muscle with greater
leverage.
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• Active insufficiency: a muscle is weak
because of a decrease in the number of
myosin-actin cross-bridges during the
sliding filament mechanism
• Can be “shortened” or “lengthened”
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• Shortened active insufficiency
– Occurs when a muscle is shorter than its
resting length
• Lengthened active insufficiency
– Occurs when a muscle is longer than its
resting length
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Figure 14-3
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Figure 14-3
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Figure 14-4
(Courtesy Joseph E. Muscolino).
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Figure 14-4
(Courtesy Joseph E. Muscolino).
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21
 Length-tension
relationship curve:
• Compares length of a sarcomere with the
percentage of maximal contraction that the
sarcomere can generate
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Figure 14-5
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 Lessened
active tension when muscle is
shortened = shortened active
insufficiency
 When muscle is lengthened =
lengthened active insufficiency
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Figure 14-6
Modified from Neumann DA: Kinesiology of the musculoskeletal system:
foundations for physical rehabilitation, ed 2, St Louis, 2010, Mosby.
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25
 Leverage: the
mechanical advantage that
a force can have when moving an object
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 Internal
forces: generated internally, from
within the body
 External forces: created externally,
outside the body
• Gravity is the most common
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 Lever: a
rigid bar that can move
 Movement occurs at axis of motion
 Distance from axis to point of application
of force = lever arm
• Sometimes referred to as a moment arm or effort
arm
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 The
longer the lever arm, the less effort it
takes to move the lever.
 Mechanical advantage: the advantage of
being able to move heavy objects with
less effort.

I believe it was Archimedes, an Early Greek “natural
philosopher “ (read scientist) who said “Give me a long
enough lever and I could move the earth.”
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Figure 14-7
Figure 14-8
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 Bones
= levers
 Muscles create
forces to move
bones
 Joints = axes of
motion
Figure 14-9
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31
 Explain
why a muscle with an attachment
that has less than an optimal angle of pull
loses extrinsic strength.
 Explain how to determine the lever arm
of a muscle.
 List the three classes of levers and give a
mechanical object and muscular
example of each one.
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32
 Define
the resistance force to a muscle’s
contraction and give two examples of a
resistance force.
 You might do this to see if you can:
Sketch a region of the body where a
muscle is contracting, and draw in the
arrows that represent the force of the
muscle contraction and the resistance
force that opposes the muscle
contraction.
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33
 Angle
of pull must be considered
 Optimal angle of pull:
• As a rule, optimal angle is perpendicular to the
long axis of its bone.
• If angle is oblique, not all the force will go
toward moving the bone.
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Figure 14-10
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Figure 14-11
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 Musculoskeletal
lever arm = shortest
distance from the center of the joint to
the line of the pull of the muscle
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Figure 14-12
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 First-, second-, and
third-class
 The difference is the relative location of
the application of force to cause
movement (F) and the force of resistance
to movement (R) relative to the axis of
motion (A).
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Figure 14-13
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 First-class
sides of A
levers: F and R on opposite
Figure 14-14
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 Second-class
levers: F and R on same
side of A (and F is farther from A)
Figure 14-15
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 Third-class
levers: F and R on same side
of A (and R is farther from A)
Figure 14-16
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 Muscles
often at mechanical
disadvantage when working against a
force with greater leverage
 This is the resistance force.
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Figure 14-6
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