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Chapter 9B
Gross Anatomy and
Functions of
Skeletal Muscles
Back Muscles
• These muscles extend, laterally flex, and rotate
the vertebral column. They also hold the
vertebral column erect
• A superficial group of muscles, the Erector
spinae, runs from the pelvis to the skull,
extending from the vertebrae to the ribs
– Consist of three subgroups on each side of the
vertebrae: Iliocostalis, Longissimus, and Spinalis
– Lateral bending of the back is accomplished by
unilateral contraction of these muscles
Fig. 9.10
Tab. 9.6
Abdominal Wall Muscles
• 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
• In addition to forming the abdominal wall, these
muscles:
– Are involved with lateral flexion and rotation of the
trunk
– Aid in functions such as forced expirations (coughing
and screaming), vomiting, defecation, urination, and
childbirth
Fig. 9.11
Tab. 9.7
Pelvic Floor and Perineum
• 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
• Two sphincter muscles allow voluntary control of
urination (External urethral sphincter) and
defecation (External anal sphincter)
• The Ischiocavernosus and Bulbospongiosus
assist in erection of the penis and clitoris
Fig. 9.12
Tab. 9.8
Thoracic Muscles
• Mainly involved in the process of breathing
• Diaphragm: most important muscle in
respiration
• External intercostals: more superficial
layer that lifts the rib cage and increases
thoracic volume to allow inspiration
• Internal intercostals: deeper layer that
aids in forced expiration
Fig. 9.13
Tab. 9.9
Scapular Muscles and Movements
• The scapula is attached to the rest of the
skeleton only by the clavicle
• Six muscles attach the scapula to the trunk and
enable the scapula to function as an anchor
point for the muscles and bones of the arm
–
–
–
–
–
Trapezius
Levator scapulae
Rhomboideus (major and minor)
Serratus anterior
Pectoralis minor
• Prime movers of shoulder elevation are the
trapezius and levator scapulae
Fig. 9.14
Tab.
9.10
Upper Limb Muscles and Arm Movements
• Nine muscles attach the humerus to the scapula.
Two additional muscles attach the humerus to
the trunk
• Trunk muscles moving the arm:
– Pectoralis major: flexes the extended shoulder and
extends the flexed shoulder
– Latissimus dorsi: adducts and medially rotates arm;
shoulder extension
• Muscles located in the shoulder moving the arm:
– Posterior fibers of the deltoid: shoulder extension
– Anterior fibers of the deltoid: shoulder flexion
– Lateral fibers of the deltoid: arm abduction and
rotation
– Teres major: shoulder extension
Fig. 9.15
Fig. 9.16
Tab.
9.11
Upper Limb Muscles and Arm Movements
• Muscles located in the shoulder that move the
arm (cont):
– Rotator cuff muscles: Supraspinatus, Infraspinatus,
Teres minor, and Subscapularis (mnemonic SITS)
• Function mainly to reinforce the capsule of the shoulder by
holding the head of the humerus in the glenoid cavity
• Secondarily act as synergists and fixators
• Muscles located in the arm that move the arm
– Coracobrachialis
– Biceps brachii
– Triceps brachii
• Actions of the trunk, shoulder, and arm muscles
on the shoulder and arm are summarized in
Table 9.12
Fig. 9.17
Tab.
9.12
Upper Limb Muscles and Forearm Movements
• Flexion and extension of the elbow are accomplished by
three muscles located in the arm and two in the forearm
• Most anterior muscles are flexors, and posterior muscles
are extensors
– Forearm flexion
• Brachialis and Biceps brachii are the chief forearm flexors
• The Brachioradialis acts as a synergist and helps stabilize the elbow
– Forearm extension
• The Triceps brachii is the prime mover of forearm extension
• The Anconeus is a weak synergist
• Supination and pronation are accomplished primarily by
forearm muscles
– The Supinator muscle is a synergist with the Biceps brachii in
supinating the forearm
– The Pronator teres and Pronator quadratus pronate the forearm
Fig. 9.18
Forearm Muscles and Wrist, Hand, and
Finger Movements
• Most anterior muscles are flexors, and posterior muscles
are extensors
• Forearm muscles
– Muscles that originate on the medial epicondyle are responsible
for flexion of the wrist and fingers
– Muscles extending the wrist and fingers originate on the lateral
epicondyle
– Forearm muscles moving the wrist, hand and fingers are
summarized in Table 9.14
• Extrinsic hand muscles are in the forearm
– Retinaculum: covers the flexor and extensor tendons and holds
them in place around the wrist
• Intrinsic hand muscles are in the hand
– Thenar muscles, hypothenar muscles, midpalmar muscles
Fig. 9.19
Fig. 9.20
Hip and Lower Limb Muscles
• Most anterior compartment muscles of the
hip and thigh flex the femur at the hip and
extend the leg at the knee
• Posterior compartment muscles of the hip
and thigh extend the thigh and flex the leg
• The medial compartment muscles all
adduct the thigh
• These three groups are enclosed by the
fascia lata
Hip Muscles and Thigh Movements
• Gluteus maximus extends the hip
• Gluteus medius and minimus help hold the
hip level while walking or running
• Deep hip muscles laterally rotate the thigh
• Anterior hip muscles flex the hip
• The thigh can be divided into three
compartments
– Anterior muscles flex the hip
– Posterior muscles extend the hip
– Medial muscles adduct the thigh
Fig. 9.21
Thigh Muscles and Leg Movements
• Anterior thigh muscles
– Quadriceps femoris: extends the knee
– Sartorius: flexes the knee
– Tensor fasciae latae: stabilizes the knee
• Posterior thigh muscles flex the knee
• One medial thigh muscle flexes the knee:
Gracilis
• Summarized in Table 9.16
Fig. 9.22
Tab.
9.16
Fig. 9.23
Tab.
9.17
Lower Limb Muscles and
Ankle, Foot, and Toe Movements
• The leg is divided into three compartments
– Muscles in the anterior compartment cause
dorsiflexion, inversion, or eversion of the foot and
extension of the toes
– Muscles of the lateral compartment plantar flex and
evert the foot
– Muscles of the posterior compartment flex the leg,
plantar flex and invert the foot, and flex the toes
• Intrinsic foot muscles flex or extend and abduct
or adduct the toes
• Summarized in Table 9.18
Fig. 9.25
Fig. 9.26