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Chapter 10
Muscular System
Introduction


There are more
than 600 skeletal
muscles in the body
From 40% to 50%
of our body weight
is skeletal muscle
Introduction


Muscles, along with the skeleton,
determine the form and contour of our
body.
The manner in which muscles are grouped,
the relationship of muscles to joints, and
how muscles attach to the skeleton
determine purposeful body movement.
Skeletal Muscle Structure
(figure 10-3)

Connective tissue
components


Endomysium –
delicate connective
tissue membrane
that covers muscle
fibers
Perimysium – tough
connective tissue
binding together
fascicles (Groups of
skeletal muscle
fibers are called
fascicles)
Skeletal Muscle Structure
(figure 10-3)

Connective tissue
components


Epimysium –
Coarse sheath
covering the muscle
as a whole
Tendon – A strong
tough cord
continuous at its
other end with a
fibrous periosteum
covering a bone
Skeletal Muscle Structure
(figure 10-3)

Connective tissue
components
 Aponeurosis –
Fibrous
wrapping of a
muscle that may
extend as a broad
sheet of
connective tissue
Skeletal Muscle Structure
(figure 10-3)

Connective tissue components
 Fascia - Fibrous connective tissue
surrounding the muscle organ and
outside the epimysium and tendon
(Fascia is a general term for the fibrous
connective tissue found under the skin
and surrounding many deeper organs,
including skeletal muscles and bones
Skeletal Muscle Structure
(figure 10-3)

Connective tissue
components

Tendon sheaths
are tube – shaped
structures of
fibrous
connective tissue
that enclose
certain tendons,
notably those of
the wrist and
ankle.
Size shape, and fiber arrangement
(figure 10-4)


Skeletal muscles vary considerably in
size, shape, and fiber arrangement
Size – range from extremely small to
large masses
Size shape, and fiber arrangement
(figure 10-4)

Shape – variety of
shapes, such as, broad,
narrow, long, tapering,
short, blunt, triangular,
quadrilateral, irregular,
flat sheets, or bulky
masses
Size shape, and fiber arrangement
(figure 10-4)

Shape – variety of
shapes, such as, broad,
narrow, long, tapering,
short, blunt, triangular,
quadrilateral, irregular,
flat sheets, or bulky
masses
Size shape, and fiber arrangement
(figure 10-4)

Arrangement – Variety of
arrangements (parallel to
long axis, converge to a
narrow attachment,
oblique, pinnate,
bipennate, or curved; the
direction of fibers is
significant due to its
relationship to function
Attachment of muscles
(figure 10-5)

Origin – Point of
attachment that does
not move when the
muscle contracts
Attachment of muscles
(figure 10-5)

Insertion- Point of
attachment that moves
when the muscle
contracts
Attachment of muscles
(figure 10-5)

A muscle is attached to
the femur and the tibia.
Its function or action is
to bend the knee.
When it contracts, it
bends the knees, so the
tibia attachment is the
insertion
Muscle actions


Skeletal muscles almost always act in
groups rather than singly.
Prime mover (agonist) - is used to
describe the muscle or group of muscles
that directly performs a specific
movement
Muscle actions


Prime mover (agonist) - is used to
describe the muscle or group of muscles
that directly performs a specific
movement
Action (function) – Is the movement
produced by a muscle acting as a prime
mover
Muscle actions

Antagonists
 Are muscles that when contracting
directly opposed prime movers
(agonists).
 They are relaxed while the prime
mover is contracting to produce
movement
Muscle actions

Synergists


Are muscles that contract at the same time as the
prime mover
They complement prime mover actions so that
the prime mover produces a more effective
movement
Muscle actions

Fixator muscles function as joint stabilizers /
They maintain posture or balance during
contraction of prime movers
Lever systems

In the human body bones serve as levers and
joints serve as fulcrums; contracting muscle
applies a pulling force on a bone lever at the
point of the muscle’s attachment to the bone,
causing the insertion bone to move about its
joint fulcrum
Lever systems

The lever system is
composed of four
parts (figure 10-6)

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Rigid bar (bone)
Fulcrum (F) around
which the rod moves
(joint)
Load (L) that is
moved
Pull (P) that produces
movement (muscle
contraction)
Lever systems

First class levers


Fulcrum lies
between the pull
and the load
Not abundant in
the human body;
serve as levers of
stability
Lever systems

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
Lever systems

Third class levers
 Pull is exerted
between the fulcrum
and load (weight to
be moved)
 Permit rapid and
extensive movement
 Most common type
of lever found
Lever systems

Third class lever
How Muscles are Named


Muscle names can be in Latin or English
Muscles are named using one or more of the
following:

Location (See table 10-1)
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

Many muscles are named as a result of location
Brachialis (arm) muscle
Gluteus (buttock) muscles
How Muscles are Named
How Muscles are Named

Function (See table
10-2)
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The function of a
muscle is frequently
part of its name
Adductor muscles of
the thigh adduct, or
move, the leg toward
the midline of the body
How Muscles are Named

Shape

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Shape is a descriptive
feature used for
naming muscles
Deltoid (triangular)
muscle covering the
shoulder is delta, or
triangular in shape.
How Muscles are Named

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Direction of fibers.
Muscles may be named
according to the
orientation of their fibers
The term rectus means
straight.
The fibers of the rectus
abdominis muscle run
straight up and down and
are parallel to each other
How Muscles are Named

Number of heads or
divisions (points of
origin

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The biceps have two
Triceps have three
Quadriceps have four
The biceps brachii is a
muscle having two
heads located in the
arm
How Muscles are Named
How Muscles are Named

Points of attachment


Origin and insertion
points may be used to
name a muscle
Sternocleidomastoid
has its origin on the
sternum and clavicle
and inserts on the
mastoid process of the
temporal bone
How Muscles are Named

Size of muscle


The relative size of a
muscle, especially if it
is compared to the size
nearby muscles
Gluteus maximus is the
largest muscle of the
gluteal region
Important muscles of the Head

Epicranius – Raises
eyebrows, wrinkles
forehead horizontally
Important muscles of the Head

Corrugator supercilii –
Wrinkles forehead
vertically (frowning)
Important muscles of the Head

Orbicularis oculi –
Closes eyes
Important muscles of the Head

Buccinator – permits
smiling
Important muscles of the Head

Pterygoids – Grates
teeth (mastification –
chewing)
Important muscles of the Head

Sternocleidomastoid –
Flexes head (prayer
muscle)
Muscles that move the Forearm

Biceps brachii


Flexes supinated
forearm
Use when pushing an
object (weight) overhead
Muscles that move the Forearm

Brachialis


Flexes pronated forearm
Uses when flexing your
muscles
Muscles that move the Forearm

Triceps brachii –
Extends lower arm
Muscles that move the lower leg
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
Include muscles that move the ankle and foot
The pelvic girdles and lower extremity function
in locomotion and maintenance of stability
Muscles that move the lower leg

Hamstring group –
Posterior of thigh



Biceps femoris – flexes
leg
Semitendinosus –
extends thigh
Semimembranosus –
extends thigh
Muscles that move the lower leg

Biceps Femoris
Muscles that move the lower leg

Semitendinosus
Muscles that move the lower leg

Semimembranosus
Muscles that move the lower leg

Quadricepts femoris
group
Muscles that move the lower leg

Sartorius
Posture
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Maintaining the posture of the body is one of the
main roles muscles play
Good posture – body alignment that most favors
function, requires the least muscular work to
maintain keeping the body’s center of gravity
over its base
Posture

How maintained
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Muscles exert a continual pull on bones in the
opposite direction from gravity
Structures other than muscle and bones have a role in
maintaining posture
Posture

The following systems help maintain posture
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Nervous system
Respiratory system
Excretory system
Endorcirne systems
Cycle of life: Muscular System

Muscle cells – increase or decrease in
number, size and ability to shorten at
different periods
Cycle of life: Muscular System

Pathological conditions at different periods
may affect the muscular system
Cycle of life: Muscular System

Life cycle changes – Infancy and childhood
changes in coordination and controlling
muscle contraction
Cycle of life: Muscular System

Degenerative changes of advancing age
result in replacement of muscle cells with
nonfunctional connective tissue. This results
in diminished strength.