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Anatomy and Physiology
Chapter 11:
Anatomy of the Muscular System
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Introduction



More than 600 skeletal muscles in
the body
From 40% to 50% of our body weight
is skeletal muscle
Muscles fill in the form and contour of
the body
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Types and Functions of Muscles
Skeletal
muscle
Smooth
muscle
Cardiac
muscle
3
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Muscle Tissue Categories
• Skeletal
• Voluntary
• Striated
• Smooth
• Involuntary
• No striations
• Cardiac
• Involuntary
• Striated
• Intercalated disks
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Whole Muscle Structure
• Fascia
• Endomysium:
each fiber
• Perimysium:
other fasicles
• Epimysium:
cover entire
muscle
• Tendon:
connect to bone
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Skeletal Muscle Organization
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Skeletal Muscle Structure

Size, shape, and fiber arrangement
Size—from extremely small to large
masses
 Shape—variety of shapes
 Arrangement—variety of arrangements,
such as parallel to a long axis, converging
to a narrow attachment, oblique, pennate,
bipennate, or curved
 Direction of fibers = relationship to function

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How Skeletal Muscles Are Named
Size: Gluteus maximus
Shape: Trapezius
Direction of fibers: Rectus abdominis
Location: Pectoralis
Number of origins: Biceps
Origin and insertion: Sternocleidomastoid
Muscle action: Adductors
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Skeletal Muscle Structure

Attachment of muscles (Figure 11-3)


Origin—point of attachment that DOES
NOT MOVE when the muscle contracts
Insertion—point of attachment that
MOVES when the muscle contracts
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Muscle actions (Figure 11-4)
Coordinated action of several
muscles
Some muscles contract while others
relax
 Prime mover—a muscle that
directly performs a specific
movement

Agonists—any “mover” muscle that
directly performs a movement
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Most movements (cont)
Synergists—contract at the same time
as the prime movers
Help prime mover to be more
efficient
 Fixator muscles—joint stabilizers

Antagonist—oppose prime movers


Relax while the prime mover is
contracting
Provide precision and control during
contraction of prime movers
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Skeletal Muscle Structure

Lever systems
Bones serve as levers
 Joints serve as fulcrums
 Contracting muscle applies a
pulling force

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Lever systems (cont)

Lever systems (cont)

Lever system—4 parts (Figure 11-5)
 Rigid bar (bone)
 Fulcrum (F) around which the rod
moves (joint)
 Load (L) that is moved
 Pull (P) that produces movement
(muscle contraction)
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Lever systems (cont)

First-class levers
• Fulcrum between the pull and the load
• Not abundant in the human body
• Serve as levers of stability

Second-class levers


Load lies between the fulcrum and the joint at
which the pull is exerted
Presence of these levers in the human body is
a controversial issue
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Lever systems (cont)

Third-class levers
• Pull is exerted between the fulcrum
and load
• Permit rapid and extensive
movement
• Most common type of lever found
in the body
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How Muscles are Named


Can be in Latin or English
Named according to one or more of the
following features:


Location, function, shape
Direction of fibers—named according to fiber
orientation

Number of heads or divisions

Points of attachment—origin and insertion points

Relative size—small, medium, or large
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Important Skeletal Muscles
(Figure 11-6)

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Muscles of facial expression- 1 point of
attachment is to the deep layers of the skin

Orbicularis oculi (eye)

Orbicularis oris (mouth)
Muscles of mastication—responsible for
chewing movements


Zygomaticus major
Massester + Buccinator = cheeks (chewing)
Muscles that move the head—paired muscles
on either side of the neck

Sternoclediomastoid
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Trunk Muscles
Aponeurosis-large flat tendon

Muscles of the thorax—of critical importance in
respiration

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Muscles of the abdominal wall- 3 layers, in
different directions to increase strength

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Rectus Transverse Oblique
Muscles of the back—bend or stabilize the back


Diaphragm
Trapezius
Latissimus Dorsi
Muscles of the pelvic floor: support the structures
in the pelvic cavity
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Posture
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Maintaining body posture is a major role
of muscles
“Good posture”—body alignment that
most favors function;
Achieved by keeping the body’s center
of gravity over its base
Least muscular work to maintain
Continual pull on bones in the opposite
direction from gravity
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Cycle of Life: Muscular System
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Muscle cells—increase or decrease in
number, size, and ability to shorten at
different periods
Life style changes will affect muscle size
and growth.

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Muscle Hypertrophy= increased muscle
size
Atrophy= decreased muscle size
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