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The Muscular System
Part C
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
08
Trunk Movements: Deep Back Muscles
 The prime mover of back extension is the erector
spinae
 Erector spinae, or sacrospinalis, muscles consist of
three columns on each side of the vertebrae –
iliocostalis, longissimus, and spinalis
 Lateral bending of the back is accomplished by
unilateral contraction of these muscles
 Other deep back extensors include the semispinalis
muscles and the quadratus lumborum
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Posterior Muscles

Name: Erector Spinae

Origin:


Insertion:


Iliac crest, ribs 3-12,
and vertebrae
Ribs thoracic /
cervical vertebrae
Primary action:

Extends back
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Name: Quadratus Lumborum
Origin:
iliac crest and iliolumbar ligament
Insertion:
Last rib and transverse processes of
lumbar vertebrae
Primary action:
Alone, lateral flexion of vertebral column;
Together, depression of thoracic rib cage
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Trunk Movements: Deep Back Muscles
Figure 10.9d
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Trunk Movements: Short Muscles
 Four short muscles
extend from one
vertebra to another
 These muscles are
synergists in
extension and
rotation of the
spine
Figure 10.9e
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Muscles of Respiration
 The primary function
of deep thoracic
muscles is to
promote movement
for breathing
 External intercostals
– more superficial
layer that lifts the rib
cage and increases
thoracic volume to
allow inspiration
Figure 10.10a
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Name: External intercostals
Origin: lower border of ribs
Insertion: upper border of rib below
Primary action: Inhalation
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Muscles of Respiration
 Internal intercostals –
deeper layer that aids in
forced expiration
 Diaphragm – most
important muscle in
inspiration
Figure 10.10a
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Name: Internal intercostals
Origin: rib - inferior border
Insertion: rib - superior border
Primary action: hold ribs steady
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Muscles of Respiration: The Diaphragm
Figure 10.10b
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Name: Diaphragm
Primary action: Functions in
breathing.
During inhalation, the diaphragm
contracts, thus enlarging the
thoracic cavity (the external
intercostal muscles also participate
in this enlargement).
When the diaphragm relaxes, air is
exhaled by elastic recoil of the lung
in conjunction with the abdominal
muscles, which act as an antagonist
paired with the diaphragm's
contraction.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Muscles of the Abdominal Wall
 The abdominal wall is composed of four paired
muscles (internal and external obliques, transversus
abdominis, and rectus abdominis), their fasciae, and
their aponeuroses
 Fascicles of these muscles run at right and oblique
angles to one another, giving the abdominal wall
added strength
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Muscles of the Abdominal Wall
 In addition to forming the abdominal wall, these
muscles:
 Are involved with lateral flexion and rotation of
the trunk
 Help promote urination, defecation, childbirth,
vomiting, coughing, and screaming
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Muscles of Abdominal Girdle

Name: External Oblique

Origin:


Insertion:


Lower 8 ribs
Iliac crest
Primary action:

Flexes and rotates
vertebral column
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Muscles of Abdominal Girdle

Name: Internal Oblique

Origin:


Insertion:


Iliac crest
Last 3 ribs
Primary action:


Paired muscles deep to
external obliques
Flex and rotate
vertebral column
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Muscles of Abdominal Girdle


Name: Transverus
abdominis
Origin:


Insertion:


Lower ribs and iliac
crest
Pubis
Primary action:

Compresses abdominal
contents
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Muscles of Abdominal Girdle


Name: Rectus
abdominis
Origin:


Insertion:


Pubis
Sternum and 5th to 7th
rib
Primary action:

Flexes vertebral
column
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Muscles of the Abdominal Wall
Figure 10.11a
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Muscles of the Abdominal Wall
Figure 10.11b
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Muscles of the Abdominal Wall
Figure 10.11c
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Muscles of the Pelvic Floor (Pelvic Diaphragm)
 The pelvic diaphragm is composed of two paired
muscles – levator ani and coccygeus
 These muscles:
 Close the inferior outlet of the pelvis
 Support the pelvic floor
 Elevate the pelvic floor to help release feces
 Resist increased intra-abdominal pressure
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Muscles Inferior to the Pelvic Floor
 Two sphincter muscles allow voluntary control of
urination (sphincter urethrae) and defecation
(external anal sphincter)
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Extrinsic Shoulder Muscles
 Muscles of the thorax
 Anterior: pectoralis major, pectoralis minor,
serratus anterior, and subclavius
 Posterior: latissimus dorsi, trapezius muscles,
levator scapulae, and rhomboids
 These muscles are involved with the movements of
the scapula including elevation, depression,
rotation, and lateral and medial movements
 Prime movers of shoulder elevation are the
trapezius and levator scapulae
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Extrinsic Shoulder Muscles
Figure 10.13a
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Extrinsic Shoulder Muscles
Figure 10.13b
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Anterior Muscles

Name: Pectoralis Major

Origin:


Insertion:


Sternum, clavicle, & 1st
to 6th rib
Proximal humerus
Primary action:

Adducts and flexes
humerus
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Name: Pectoralis minor
Origin:
third to fifth ribs, near their
costal cartilages
Insertion: Scapula
Primary action:
Stabilizes scapula
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Name: Serratus anterior
Origin: outer surface of
upper 8 or 9 ribs
Insertion: costal aspect of
medial margin of the
scapula
Primary action:
protracts and stabilizes
scapula, assists in upward
rotation
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Name: Subclavius
Origin: first rib
Insertion: subclavian groove of
clavicle
Primary action:
depression of clavicle
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
Name: Latissimus Dorsi

Origin:


Insertion:


Lower spine and iliac
crest
Proximal humerus
Primary action:

Extends and adducts
humerous
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
Name: Trapezius

Origin:


Insertion:


Occipital bone and all
cervical / thoracic
vertebrae
Scapular spine and
clavicle
Primary action:

Extends neck and
adducts scapula
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Name: Levator scapulae
Origin: C1 - C4 vertebrae
Insertion: scapula
Primary action:
Elevates scapula and tilts its
glenoid cavity inferiorly by
rotating scapula
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Name: Rhomboids
Origin: C7 to T5 vertebrae
Insertion: scapula
Primary action:
Retracts the scapula and
rotates it to depress the
glenoid cavity. It also fixes
the scapula to the thoracic
wall.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings