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prepared by
Barbara Heard,
Atlantic Cape Community
College
CHAPTER
10
The
Muscular
System:
Part A
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
The Muscular System
• Muscle tissue – all contractile tissues
– Skeletal, cardiac, smooth muscle
• Focus on skeletal muscle
– How muscles interact to  movement
– Criteria for naming muscles
– Principles of leverage
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Actions and Interactions of Skeletal Muscles
• Muscles can only pull; never push
• What one muscle group "does", another
"undoes"
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Actions and Interactions of Skeletal Muscles
• Functional Groups
– Prime mover (agonist)
• Major responsibility for producing specific
movement
– Antagonist
• Opposes or reverses particular movement
– Prime mover and antagonist on opposite
sides of joint across which they act
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Figure 10.1 The action of a muscle can be inferred by the position of the muscle relative to the joint it crosses.
(Examples given relate to the shoulder joint.)
A muscle that crosses on the anterior side of a joint produces flexion*
Example:
Pectoralis major
(anterior view)
A muscle that crosses on the posterior side of a joint produces extension*
Example: Latissimus
dorsi (posterior view)
The latissimus dorsi
is the antagonist of
the pectoralis major.
A muscle that crosses on the lateral side of a joint produces abduction
Example: Deltoid
middle fibers
(anterolateral view).
A muscle that crosses on the medial side of a joint produces adduction
Example:
Teres major
(posterolateral view)
The teres major is the
antagonist of the
deltoid.
*These generalities do not apply to the knee and ankle because the lower limb is rotated during development. The
muscles that cross these joints posteriorly produce flexion, and those that cross anteriorly produce extension.
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Skeletal Muscles: Functional Groups
• Same muscle may be
– Prime mover of one movement
– Antagonist for different movement
– Synergist for third movement
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Naming Skeletal Muscles
• Muscle location—bone or body region with
which muscle associated
• Muscle shape—e.g., deltoid muscle (deltoid =
triangle)
• Muscle size—e.g., maximus (largest), minimus
(smallest), longus (long)
• Direction of muscle fibers or fascicles—e.g.,
rectus (fibers run straight), transversus (fibers
run at right angles), and oblique (fibers run at
angles to imaginary defined axis)
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Naming Skeletal Muscles
• Number of origins—e.g., biceps
(2 origins) and triceps (3 origins)
• Location of attachments—named
according to point of origin and insertion
(origin named first)
• Muscle action—named for action they
produce, e.g., flexor or extensor
• Several criteria can be combined, e.g.,
extensor carpi radialis longus
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Figure 10.5 Superficial muscles of the body: Anterior view.
Facial
Epicranius, frontal belly
Head
Temporalis
Masseter
Shoulder
Trapezius
Deltoid
Arm
Triceps brachii
Biceps brachii
Brachialis
Forearm
Pronator teres
Brachioradialis
Flexor carpi radialis
Palmaris longus
Pelvis/thigh
Iliopsoas
Pectineus
Thigh
Rectus femoris
Vastus lateralis
Vastus medialis
Leg
Fibularis longus
Extensor digitorum
longus
Tibialis anterior
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Orbicularis oculi
Zygomaticus
Orbicularis oris
Neck
Platysma
Sternohyoid
Sternocleidomastoid
Thorax
Pectoralis minor
Pectoralis major
Serratus anterior
Intercostals
Abdomen
Rectus abdominis
External oblique
Internal oblique
Transversus abdominis
Thigh
Tensor fasciae latae
Sartorius
Adductor longus
Gracilis
Leg
Gastrocnemius
Soleus
Figure 10.6 Superficial muscles of the body: Posterior view.
Arm
Triceps brachii
Brachialis
Forearm
Brachioradialis
Extensor carpi radialis
longus
Flexor carpi ulnaris
Extensor digitorum
Extensor carpi ulnaris
Iliotibial tract
Leg
Gastrocnemius
Soleus
Fibularis longus
Calcaneal
(Achilles) tendon
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Neck
Epicranius, occipital belly
Sternocleidomastoid
Trapezius
Shoulder
Deltoid
Infraspinatus
Teres major
Rhomboid major
Latissimus dorsi
Hip
Gluteus medius
Gluteus maximus
Thigh
Adductor magnus
Hamstrings:
Biceps femoris
Semitendinosus
Semimembranosus
Muscles of the Head
• Two groups
– Muscles of facial expression
– Muscles of mastication and tongue movement
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Muscles of Mastication
• Four pairs involved in mastication; all
innervated by cranial nerve V (trigeminal
nerve)
– Prime movers of jaw closure
• Temporalis and masseter
– Grinding movements
• Medial and lateral pterygoids
– Chewing role - holds food between teeth
• Buccinator
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Figure 10.8a Muscles promoting mastication and tongue movements.
Temporalis
Orbicularis
oris
Buccinator
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Masseters
Figure 10.8b Muscles promoting mastication and tongue movements.
Lateral
pterygoid
Medial
pterygoid
Masseter
pulled away
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Muscles of the Anterior Neck and Throat
• Two groups
– Suprahyoid muscles
– Infrahyoid muscles
• Most involved in swallowing
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Muscles of the Neck and Vertebral Column
• Two functional groups
– Muscles that move head
– Muscles that extend trunk and maintain
posture
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Muscles of the Neck and Vertebral Column:
Head Movement
• Sternocleidomastoid—major head flexor
– Suprahyoid and infrahyoid—synergists to
head flexion
• Sternocleidomastoid and scalenes—
lateral head movements
• Splenius capitis and cervicis portions head extension, rotation, and lateral
bending
• Semispinalis capitis—synergist with
sternocleidomastoid
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Figure 10.10a Muscles of the neck and vertebral column that move the head and trunk.
1st cervical
vertebra
Sternocleidomastoid
Base of
occipital bone
Mastoid
process
Middle
scalene
Anterior
scalene
Posterior
scalene
Anterior
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Figure 10.10c Muscles of the neck and vertebral column that move the head and trunk.
Platysma (cut)
Sternocleidomastoid
(cut)
Internal jugular vein
Omohyoid
Sternohyoid
Sternothyroid
Sternocleidomastoid
Pectoralis major
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Muscles of the Neck and Vertebral Column:
Trunk Extension
• Deep (intrinsic) back muscles
– Erector spinae (sacrospinalis) group—
prime movers of back extension and lateral
bending
• Iliocostalis
• Longissimus
• Spinalis
– Semispinalis and quadratus lumborum—
synergists in extension and rotation
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Figure 10.10d Muscles of the neck and vertebral column that move the head and trunk.
Mastoid process
of temporal bone
Longissimus capitis
Iliocostalis cervicis
Longissimus cervicis
Iliocostalis thoracis
Ligamentum
nuchae
Semispinalis
capitis
Semispinalis
cervicis
Semispinalis
thoracis
Longissimus thoracis
Spinalis thoracis
Iliocostalis
Erector Longissimus
spinae
Spinalis
Iliocostalis
lumborum
External oblique
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Multifidus
Quadratus
lumborum
Deep Muscles of the Thorax: Breathing
• Muscles of respiration
• External intercostals—more superficial
muscles; elevate ribs for inspiration
• Internal intercostals—deeper muscles;
aid forced expiration
• Diaphragm
– Partition between thoracic and abdominal
cavities
– Most important muscle in inspiration
– Innervated by phrenic nerves
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Figure 10.11a Muscles of respiration.
External
intercostal
Internal
intercostal
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Figure 10.11b Muscles of respiration.
Xiphoid process of sternum
Foramen for inferior
vena cava
Foramen for
esophagus
Costal cartilage
Central
tendon of
diaphragm
Foramen
for aorta
12th rib
Diaphragm
Lumbar
vertebra
Quadratus
lumborum
Psoas major
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Figure 10.11c Muscles of respiration.
Central tendon of diaphragm
Body of thoracic vertebra
Aorta
Diaphragm (muscular part)
Inferior vena cava
Esophagus
Pericardial sac
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Pericardium (cut)
Muscles of the Abdominal Wall
• Four paired muscles, their fasciae and
aponeuroses form lateral and anterior
abdominal wall
– Rectus abdominis
– External obliques
– Internal obliques
– Transversus abdominis
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Figure 10.12a Muscles of the abdominal wall.
Pectoralis major
Serratus anterior
Linea alba
Tendinous intersection
Transversus abdominis
Rectus abdominis
Internal oblique
External oblique
Aponeurosis
of the external
oblique
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Inguinal ligament
(formed by free inferior
border of the external
oblique aponeurosis)
Muscles of the Abdominal Wall
• run at angles to one another, provide
added strength
• All innervated by intercostal nerves
• Actions of these muscles
– Lateral flexion and rotation of trunk
– Help promote urination, defecation, childbirth,
vomiting, coughing, and screaming
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Figure 10.12b Muscles of the abdominal wall.
External
oblique
Iliac crest
Rectus
abdominis
Internal
oblique
Pubic tubercle
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Lumbar
fascia
Transversus
abdominis
Inguinal
ligament
Lumbar
fascia
Figure 10.12c Muscles of the abdominal wall.
Transversus abdominis
External oblique
Aponeuroses
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Peritoneum Linea
alba
Rectus abdominis
Internal oblique
Skin
Superficial Muscles of the Thorax
• Most - extrinsic shoulder muscles
– Act in combination to fix shoulder girdle (mostly
scapula); move it to increase range of arm
movements
– Actions - elevation, depression, rotation, lateral and
medial movements, protraction, and retraction
• Two groups of muscles: anterior and posterior
PLAY
A&P Flix™: Muscles that act on the shoulder joint
and humerus: An overview (a)
PLAY
A&P Flix™: Muscles that act on the shoulder joint
and humerus: An overview (b)
© 2013 Pearson Education, Inc.
Superficial Muscles of the Thorax
• Muscles of anterior thorax
– Pectoralis minor
– Serratus anterior
– Subclavius
PLAY
A&P Flix™: Muscles of the pectoral girdle (a)
PLAY
A&P Flix™: Muscles of the pectoral girdle (b)
© 2013 Pearson Education, Inc.
Figure 10.14a Superficial muscles of the thorax and shoulder acting on the scapula and arm.
Sternocleidomastoid
Subclavius
Clavicle
Subscapularis
Deltoid
Pectoralis minor
Pectoralis major
Sternum
Serratus anterior
Biceps brachii
PLAY
Coracobrachialis
Humerus
A&P Flix™: Muscles that act on the shoulder joint
and humerus: An overview (b)
© 2013 Pearson Education, Inc.
Superficial Muscles of the Posterior Thorax
• Posterior extrinsic shoulder muscles
– Trapezius
– Levator scapulae
– Rhomboids (major and minor)
PLAY
A&P Flix™: Muscles of the pectoral girdle (c)
PLAY
A&P Flix™: Movement of the pectoral girdle
© 2013 Pearson Education, Inc.
Figure 10.14c Superficial muscles of the thorax and shoulder acting on the scapula and arm.
Levator
scapulae
Trapezius
Supraspinatus
Clavicle
Deltoid
Rhomboid
minor
Spine of
scapula
Infraspinatus
Rhomboid
major
Teres minor
Teres
major
Humerus
Latissimus
dorsi
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