Chapter 4
Muscular System
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Davis Company
Objectives:
Explain the terms origin and insertion
Explain how muscles are named
Identify various types of muscle fiber arrangements
Differentiate the functional characteristics of muscle
tissue and the length-tension relationship
Differentiate the types of muscle contractions and
the roles of muscles
Discuss angle of pull and kinetic chains
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Muscle Attachment s
When a muscle contracts, it knows no
direction: it simply shortens
Muscle cross joints so the insertion moves
toward the origin
Most commonly, insertion (more movable
bone), toward origin (more stable bone)
Reversal of muscle action, origin moves
toward insertion
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Davis Company
Muscle Attachment s
A.
B.
(cont’d)
Insertion moves
toward origin
Origin moves
toward insertion
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Davis Company
(From Norkin, CN and Levangie, PK: Joint Structure
and Function: A Comprehensive Analysis, ed 2. FA
Davis, Philadelphia, 1992, p 107, with permission.)
Muscle Names
The name of a muscle can often tell you
great deal about that muscle:
1.
2.
3.
4.
5.
6.
7.
Location
Shape
Action
Number of heads or divisions
Attachments = origin/insertion
Direction of the fibers
Size of the muscle
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Davis Company
Muscle Names
Tibialis anterior
Rectus abdominis
Trapezius
Serratus anterior
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(cont’d)
Located anterior
surface of tibia
Vertical muscle on
abdomen
Trapezoid shape
Serrated or jaggedshaped attachment
located anteriorly
Muscle Names
Extensor carpi ulnaris
Triceps
Biceps
Sternocleidomastoid
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(cont’d)
Action to extend the
wrist, ulnar side
three-headed muscle
two-headed muscle
Attaches on sternum,
clavicle, and mastoid
bones
Muscle Names
(cont’d)
External and internal oblique
Describe the direction of the fibers and their
location
Pectoralis major and minor
Both muscles in pectoral region, one of greater
size than other
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Davis Company
Muscle Fiber Arrangement
Fibers Parallel to the
long axis of the muscle
Longer
Greater range of motion
potential
Fibers Oblique to the
long axis of the muscle
Shorter
More numerous fibers per
given area
Greater strength potential
Smaller range of motion
potential
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Davis Company
Muscle Fiber Arrangement
(cont’d)
Parallel
A.
B.
C.
D.
Strap
Fusiform
Rhomboidal
Triangular
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Oblique
E. Unipennate
F. Bipennate
G. Multipennate
Parallel
A. Strap
Long and thin, fibers run entire length
Example: Sartorius, sternocleidomastoid
B. Fusiform
Spindle shape - wide middle, tapered ends
Example: Biceps
C. Rhomboidal
Four sides,flat
Example: Rhomboids
D. Triangular
Flat, fan shaped, fibers radiating from a narrow attachment
Example: Pectoralis major
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Oblique
Pennate = feather
E. Unipennate
One side of a feather
Example: Tibialis posterior
F. Bipennate
Common feather
Example: Interossei, gastrocnemius
G. Multipennate
Many tendons
Example: Deltoid
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Functional Characteristics
of Muscle Tissue
Normal resting length
Length unstimulated, when there are no
forces or stresses upon it
Characteristics:
Irritability
Contractility
Extensibility
Elasticity
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Davis Company
Functional Characteristics of
Muscle Tissue (cont’d)
Irritability - ability to respond to a stimulus
Contracts when stimulated, motor nerve or electric current
Contractility - ability to shorten or contract
Produces tension between ends
The muscle shortens, stays the same, or lengthens
Extensibility - ability of a muscle to stretch or
lengthen when force is applied
Elasticity - Ability to recoil or return to normal
resting length when stretching or shortening force is
removed
Example: Wire spring
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Length-Tension
Relationship in Muscle Tissue
Tension
Force built up within the muscle
Shorten
Shortens ~1/2 of its normal resting length
Excursion
Distance from maximum elongation to
maximum shortening
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Davis Company
Length-Tension
Relationship in Muscle Tissue
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Davis Company
Two-Joint Muscles
Length-Tension Relationship
Muscle strongest if put on a slight stretch
before contracting
Example: Kicking a ball
First hyperextend hip and then flex it forcefully
Put hip flexors on a stretch before contracting
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Active / Passive Insufficiency
Passive Insufficiency
Active Insufficiency
When a muscle
When a muscle
cannot be elongated
reaches a point where
any farther without
it cannot shorten any
damage to the fibers
farther
Occurs to the
Occurs to the agonist
antagonist
Opposite the agonist
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Active Insufficiency
Hamstrings
two-joint muscles
Extend the hip, flex the knee
Can perform either motion but not
simultaneously
If flex knee while hip flexed, can attain full
knee flexion
If flex knee while hip extended, cannot
complete the full range
Actively Insufficient
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Passive Insufficiency
Hamstrings antagonist
Muscle can be stretched over each joint individually but not both
If you flex your hip with knee flexed, can complete the
range
Can extend knee when hip is extended
Now, sit with knee extended, flex at hip, hamstring
tightness → Passively Insufficient
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Stretching
Agonist usually becomes actively
insufficient (cannot contract any farther)
before the antagonist becomes passively
insufficient (cannot be stretched farther)
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Davis Company
Tenodesis
Tendon Action of a Muscle
(From Norkin, CN and Levangie, PK: Joint
Structure and Function: A Comprehensive
Analysis, ed 2. FA Davis, Philadelphia,
1992,p 117, with permission.)
Some opening and closing of the hand accomplished through passive
insufficiency
Long finger fingers have passive flexion through active wrist extension
Critical in individuals with tetraplegia and lack finger flexion
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Davis Company
Types of Muscle Contraction
Three basic types
1.
Isometric
⌧Muscle contracts, producing force without
changing the length of the muscle
2.
Isotonic
⌧Muscle contracts, changing the muscle length and
the joint angle
3.
Isokinetic (Cybex, Orthotron, KinCom)
⌧Resistance varies
⌧Velocity (speed) stays the same
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Davis Company
Types of Muscle Contraction
(cont’d)
A. Isometric
B. Isotonic - Concentric
C. Isotonic - Eccentric
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Isotonic Contractions
Concentric
Muscle attachments move
closer together
Movement is occurring
against gravity
A “raising” motion
If occurring with gravity,
muscle is overcoming
force greater than pull of
gravity
Contraction is used with an
acceleration activity
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Eccentric
Muscle attachments move
farther apart
Movement occurs with
gravity
A “lowering” motion
The contraction is used
with a deceleration activity
The contraction produces
greater forces
Isokinetic Contractions
Can be done only with special equipment
Cybex
Orthotron
Resistance varies but the velocity stays
the same
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Physical Therapy and Muscle
Contractions
“Setting” exercises are isometrics
Consider the difference:
Straightening the knee while sitting
Bending the knee while prone
Which is against gravity?
Which is with gravity?
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Types of Muscle Contraction
Isometric
Isotonic
Isokinetic
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Speed
Fixed
Variable
Fixed
Resistance
Fixed
Fixed
Variable
Joint Motion
No
Yes
Yes
Roles of Muscles
Agonist = Prime Mover
Assisting Mover
Antagonist
Cocontraction
Stabilizer
Neutralizer
Synergist
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Agonist = Prime Mover
Roles of Muscles
Muscle or muscle group that causes the
motion
Assisting mover
Assists the movement
Example: During elbow flexion
Biceps - agonist
Pronator teres - assisting mover
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Antagonist
Roles of Muscles
Muscle that performs the opposite
motion of the agonist
Example: During elbow flexion
Biceps - agonist
Triceps - antagonist
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Davis Company
Cocontraction
Roles of Muscles
When agonist and antagonist contract
at the same time
Occurs when there is a need for
accuracy
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Davis Company
Stabilizer
Roles of Muscles
Muscle or muscle group that supports, or
makes firm, a part and allows the agonist
to work more efficiently
Sometimes called a fixator
Example:
When doing a push-up
Triceps, elbow extensors - agonist
Abdominal muscles - stabilizers
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Davis Company
Neutralizer
Roles of Muscles
Prevents unwanted motion because a muscle
knows no direction when it contracts
May also allow a muscle to do more than one
motion
Example:
Biceps flex the elbow and supinate the forearm
If only want elbow flexion, pronator teres would
contract
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Davis Company
Synergist
Roles of Muscles
Term used to encompass role of:
Agonists
Assisting movers
Stabilizers
Neutralizers
It is a muscle that works with another muscle
to enhance a particular motion
A problem with this term is that it indicates a
muscle is working, but does not indicate how
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Davis Company
Angle of Pull
Muscles know one direction of pull
Visualizing the muscle will assist you in
knowing their action
Most muscles have a diagonal line of pull
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Davis Company
Angle of Pull
(cont’d)
A. Vertical pull Elevating or depressing
the scapula
B. Horizontal pull Retract or protract the
scapula
C. Diagonal pull Cause motion in both
planes
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Kinetic Chains
Closed Kinetic Chain
Distal segment be
fixed (closed)
Proximal segment
moves
Example:
⌧Rising from sitting
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Open Kinetic Chain
Distal segment free
to move
Proximal segment
stationary
Example:
⌧Sitting knee extension
Kinetic Chains
Closed Kinetic
Chain
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(cont’d)
Open Kinetic
Chain