Muscular System
Origins & Insertions
Origin: Muscle attachment to the more
stable bone; often closer to the trunk
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Reversal of muscle action when origin moves
towards insertion
Insertion: Muscle attachment to the more
movable bone; often distal from the trunk

Insertion usually moves towards origin
Proximal: closer to the trunk
Distal: farther from the trunk
Muscle Names
Muscle names may fall into one or more of
the following categories:
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Location
Shape
Action
Number of heads
Attachments (origin & insertion)
Direction of the Fibers
Size of the Muscle
Muscle Fiber Arrangement
Muscle Fiber Arrangement
Parallel Muscle fibers tend to be longer,
with a greater ROM potential
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Strap: long and thin c fibers running entire
length of muscle (sartorius)
Fusiform: spindle shaped (biceps)
Rhomboidal: four-sided, flat shaped (rhomboids)
Triangular: flat & fan-shaped (pec major)
Muscle Fiber Arrangement
Oblique muscle fibers tend to be shorter
with greater strength potential, but
decreased ROM
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Unipennate: one side of a feather (post. tib.)
Bipennate: common feather (rectus femoris)
Multipennate: many tendons c oblique fibers
in-between (deltoid)
Functional Characteristics of
Muscle Tissue
Five Properties of Muscles:
Normal Resting Length
Irritability
Contractility
Extensibility
Elasticity
Functional Characteristics of
Muscle Tissue
Normal Resting Length

Length of muscle when unstimulated
Functional Characteristics of
Muscle Tissue
Irritability

Ability of a muscle to respond to a stimulus. A
muscle contracts when stimulated, either from
a natural stimulus (motor nerve) or artificial
stimulus (high volt electrical current)
Functional Characteristics of
Muscle Tissue
Contractility
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Ability of a muscle to shorten (contract)
A muscle’s length may shorten, lengthen or
remain the same length during contraction
and stimulation
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Isotonic and Isometric
Concentric and Eccentric
Functional Characteristics of
Muscle Tissue
Extensibility

The ability of a muscle to stretch or lengthen
when a force is applied
Functional Characteristics of
Muscle Tissue
Elasticity

The ability of a muscle to recoil or return to
normal resting length when the stretching or
shortening force is removed
Functional Characteristics of
Muscle Tissue
“Stretch a muscle and it will lengthen
(extensibility). Remove the stretch, and it
will return to its normal resting position
(elasticity). Stimulate a muscle, and it will
respond (irritability) by shortening
(contractility).”
Length-Tension Relationship in
Muscle Tissue
Tension: The force built up in a muscle
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Stretching builds passive tension
Contractile units control active tension
Length-Tension Relationship in
Muscle Tissue
Tone: The slight tension that is present in
a muscle at all times, even at rest
Length-Tension Relationship in
Muscle Tissue
Excursion of a Muscle: The distance from
maximum elongation to maximum
shortening
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A muscle is capable of being shortened to
approximately one-half its normal resting
length
A muscle can be stretched twice as far as it
can be shortened
Active and Passive Insufficiency
Active Insufficiency: Point at which a
muscle cannot shorten any farther

Occurs to the agonist
Passive Insufficiency: Point at which a
muscle cannot elongate any farther
without damage to the muscle fibers
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Occurs to the antagonist
Muscle Contractions
Isometric Contractions: Muscle neither
lengthens or shortens under load
Isotonic Contractions:
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Concentric Contraction
Muscles shorten under load
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Eccentric Contraction
Muscles lengthen under load
Roles of Muscles
Agonist: muscle that causes motion
Antagonist: muscle that performs the opposite motion of
the agonist
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Biceps vs. Triceps
Cocontraction: agonist and antagonist contract together
Stabilizer: makes firm; allows agonist to work more
efficiently
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Abdominal muscles during a push-up (elbow extensors)
Neutralizer: prevents unwanted motion
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Pronator teres neutralizes forearm supination during elbow
flexion
Kinetic Chains
Closed Kinetic Chain
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Distal segment is fixed; proximal segment
moves
Open Kinetic Chain
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Distal segment moves; proximal segment is
fixed