Chapter 10
Muscular System
Interactions of Muscles

Muscles can be classified into 4
functional groups!
– Synergist- they help prime movers by
adding extra force, reducing unneccessary
movements.
– Fixators- Holds parts of the body in proper
position for the action of other muscles,
primarily postural muscles.
Interactions of Muscles

Muscles can be classified into 4
functional groups!
– Prime Mover- A muscle that provides the
major force for producing a specific
movement.
– Antagonists- muscles that oppose, or
reverse, a particular movement.
Muscles Work!!
Muscles never push they just pull!!
 Muscles are usually in pairs because
whatever one muscles or muscle group
can do, there is another muscle or
group of muscles that “undoes” the
action.
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Naming of the
Skeletal Muscles!
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Skeletal muscles are
named according to a
number of criteria, each
of which describes the
muscle in some way.
Paying attention to
these cues can simplify
the task of learning
muscle names and
actions.
Naming of the
Skeletal Muscles!
1. Location of the Muscle (temporalis)
 2. Shape of the Muscle (Deltoid)
 3. Relative size of the Muscle
(Maximus, minimus)
 4. Direction of the Muscle Fibers
(rectus –straight: oblique, transverse
mean to run at right angles.)

Naming of the
Skeletal Muscles!
5. Number of Origins
(triceps and biceps)
 6. Location of the attachments
(Sternocleidomastoid)
 7. Action (adductor longus)

Muscles of Facial Expression
Head/Neck
Orbicularis Oculi
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The WINKER
A ringlike band of
muscle, called a
sphincter muscle, that
surrounds the eye. It
lies in the subcutaneous
tissue of the eyelid
Closes eye in blinking
It also aids in the
compressing the tear
glands
Orbicularis Oris
The “Pucker Up”
Muscle
 Sphincter muscle
that surrounds the
lips.
 Closes and puckers
the lips.
 Often called the
“kissing muscle”

Zygomaticus

Extends from the
zygomatic arch
downward to the
corner of the mouth
 Raises corner of
mouth when
smiling and
laughing
Platysma

The Frowner
 Thin sheet like
superficial neck
muscle.
 Plays a role in facial
expression.
 Tenses skin of neck.
(e.g. during shaving)
Epicranius

The epicranius covers the upper part of
the cranium and consists of two
muscular parts.
– Frontalis and Occipitalis
Frontalis

Lies over the frontal
bone
 Wrinkles forehead
Occipitalis

Moves scalp
Sternocleidomastoid
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Praying Muscle
Long muscle in the side
of the neck that extends
upward from the thorax
to the base of the skull
behind the ear
Pulls head to one side
Masseter
“The Chewer”
 A thick flattened
muscle that can be
felt just in front of
the ear when the
teeth are clenched
 Elevates mandible
 Closes mouth

Buccinator

Blower or Whistler!!
 Thin, horizontal
cheek muscles;
 Draws corner of
mouth laterally,
compresses cheek ,
well developed in
nursing infants.
Muscles that Move
the Pectoral Girdle
Chest/Back Muscles
Trapezius
o A large triangular
muscle in the upper
back that extends
horizontally from the
base of the skull and
the cervical thoracic
vertebrae to the
shoulder
o Rotates scapula.
Rhomboideus
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The Rhomboids are
very thin muscles which
have tremendous
responsibility.
Connects the upper
thoracic vertebrae to
the scapula.
Raises the scapula and
adducts.
Serratus Anterior
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A broad curved muscle
located on the side of
the chest
Arises from narrow
strips on the upper ribs
and extends along the
medial wall of the axilla
to the ventral surface of
the scapula
Pulls scapula anteriorly
and downward
Used to thrust the
shoulder forward when
pushing something.
Muscles that move the Arm
Chest/Arm
Pectoralis Major
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A thick fan shaped
muscle located in the
upper chest.
Extends from the center
of the thorax through
the armpit to the
humerus
Adducts and medially
rotates humerus; draws
scapula anteriorly and
inferiorly.
Pulls the arm forward
and across the chest.
Pectoralis Minor

A thin, flat muscle
that lies beneath the
larger pectoralis
major
 Stabilizes scapula
by drawing it
inferiorly and
anteriorly against
thoracic wall
Teres Major

Medially rotates and
adducts arm.
 Stabilizes shoulder
joint
 Connects the
scapula to the
humerus
Teres Minor
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
Small muscle
connecting the
scapula to the
humerus.
 Rotates arm laterally
Infraspinatus

Occupies the
depression below the
spine of the scapula on
its posterior surface.
 Attach the scapula to
the humerus; helps to
hold humeral head in
glenoid cavity of
scapula.
 Laterally rotate arm
Latissimus Dorsi


It is a wide, triangular
muscle that curves
upward from the lower
back, around the sides,
and to the armpit.
Extends, adducts, and
rotates arm, pulls
shoulder down or back
Deltoid Muscle

Abducts, extends,
and flexes the arm
 It is a thick,
triangular muscle
that covers the
shoulder joint.
Muscles that Move the Forearm
Biceps Brachii
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It is a fleshy muscle that
forms a long, rounded
mass on the anterior
side of the arm
Connects the scapula to
the radius and ulna
Flexes forearm at elbow
Rotates hand laterally
Brachialis

A large muscle
beneath the biceps
brachii
 Connects the shaft
of the humerus to
the ulna
 Flexes forearm at
elbow
Brachioradialis

Connects the
humerus to the
radius.
 Flexes forearm at
elbow
Triceps Brachii
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Has three heads and is
the only muscle on the
back of the arm
Connects the humerus
and scapula to the ulna
It is the primary
extensor of the elbow.
Flexes forearm at elbow
Extensor Digitorum
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Runs medially along the
back of the forearm.
Connects the humerus
to the posterior surface
of the phalanges and
then extends the
fingers.
Extends hand at wrist
joint
Muscles of the Abdominal
Wall
External Oblique
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A broad, thin sheet of
muscle whose fibers
slant downward from
the lower ribs to the
pelvic girdle.
Tenses abdominal wall
Compresses contents
Internal Oblique
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A broad, thin sheet of
muscle located beneath
the external oblique
Runs up and forward
from the pelvic girdle to
the lower ribs.
Tenses abdominal wall
Compresses contents
Rectus Abdominis
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Long, straplike muscle
that connects the pubic
bones to the ribs and
sternum.
Tenses abdominal wall
Compresses contents
Flexes vertebral column
Muscles that make
up the Leg
Biceps femoris

Has 2 heads, one
attaches to the ischium
and the other attached to
the femur.
 Passes along the back of
the thigh on the lateral
side and connects to the
proximal ends of the fiubla
and tibia.
 Flexes and rotates leg
laterally and extends
thigh.
 1 of the hamstring
muscles
Semitendinosus
(the 2nd muscle of the hamstring)
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Semitendinosus- long
bandlike muscle on the
back of the thigh.
Connecting the ischium
to the proximal end of
the tibia.
Flexes and rotates the
leg medially and
extends the thigh
Semimembranosus
(the 3rd muscle of the hamstring)

Semimembranosus
the most medially
located muscle in the
back of the thigh; it
connects the ischium to
the tibia.

Flexes and rotates the
leg medially and
extends the thigh
Sartorius
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An elongated, straplike
muscle that passes
obliquely across the
front of the thigh and
then descends over the
medial side of the knee.
Connects the ilium to
the tibia and flexes the
leg and the thigh.
Flexes leg and thigh
Abducts and rotates
thigh laterally
Quadriceps Femoris

This is a large fleshy muscle group
 Occupies the front and sides of the thigh and
is the primary extensor of the knee
 Includes….Rectus femoris, vastus lateralis,
vastus medialis, and vastus intermedius (I am
not holding you accountable for the last one)
 These parts connect the ilium and femur to a
common patella tendon, which passes over
the front of the knee and attaches to the
patella.
Rectus Femoris
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Extends leg at knee
Vastus Lateralis
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Extends leg at knee
Vastus Medialis
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Extends leg at knee
Muscles that move
the Thigh
Gluteus Maximus
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The largest muscle in
the body and covers a
large part of each
buttock
Connects the ilium,
sacrum, and coccyx to
the femur by fascia of
the thigh and extends
the thigh.
Extends thigh at hip,
helps to straighten the
lower limb, also used to
raise the body from a
sitting position
Gluteus Medius

Partly covered by
the gluteus maxium.
 Its fibers extend
from the ilium to the
femur
 Abducts and rotates
thigh medially
Adductor Longus

A long triangular
muscle that runs
from the pubic bone
to the femur
 Adducts, flexes, and
rotates thigh
laterally
Adductor Magnus
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The largest adductor of
the thigh.
A triangular muscle that
connects the ischium to
the femur.
Adducts, extends, and
rotates thigh laterally.
Gracilis

A long straplike
muscle that passes
from the pubic bone
to the tibia.
 Adducts thigh
 Flexes leg at knee
Muscles that move
the Foot
Tibialis Anterior

An elongated, spindleshaped muscle located
on the front of the leg
 Arises from the tibia,
passes medially over
the distal end of the
tibia, and attaches to
bones of the foot
 Dorsiflexion and
inversion of foot
Extensor Digitorum
Longus

This is situated
along the lateral
side of the leg just
behind the tibialis
anterior.
 Dorsiflexion and
eversion of the foot
 Extension of toes
Gastrocnemius

On the back of the
leg forms part of the
calf.
 Plantar flexion of
foot and flexion of
leg at knee
Soleus
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A thick, flat muscle
located beneath the
gastrocnemius and
together these two
muscles form the calf of
the leg
Arises from the tibia
and fibula and extends
to the heel
Plantar flexion of foot
Fibularis Longus
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It is a long, straplike
muscle located on the
lateral side of the leg.
It connects the tibia and
the fibula to the foot.
Plantar flexion and
eversion of foot
Supports arch