352
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
Subscapularis
(sub-scap
0
u-lar
9
is)
(
sub
5
under;
scapular
5
scapula)
Forms part of posterior
wall of axilla; tendon of
insertion passes in front of
shoulder joint; a rotator
cuff muscle
O—subscapular fossa of
scapula
I—lesser tubercle of
humerus
Chief medial rotator of
humerus
; assisted by
pectoralis major; helps
hold head of humerus in
glenoid cavity, stabilizing
shoulder joint
Subscapular nerves
(C
5
–C
7
)
Supraspinatus
(soo
0
prah-spi-nah
9
tus)
(
supra
5
above, over;
spin
5
spine)
Named for its location on
posterior aspect of scapula;
deep to trapezius; a rotator
cuff muscle
O—supraspinous fossa of
scapula
I—superior part of
greater tubercle of
humerus
Initiates abduction
;
stabilizes shoulder joint;
helps prevent downward
dislocation of humerus,
as when carrying a heavy
suitcase
Suprascapular nerve
Infraspinatus
(in
0
frah-spi-nah
9
tus)
(
infra
5
below)
Partially covered by deltoid
and trapezius; named for
its scapular location; a
rotator cuff muscle
O—infraspinous fossa of
scapula
I—greater tubercle
of humerus posterior
to insertion of
supraspinatus
Rotates humerus laterally
;
helps hold head of
humerus in glenoid cavity,
stabilizing the shoulder
joint
Suprascapular nerve
Teres minor
(te
9
re
ˉ
z)
(
teres
5
round;
minor
5
lesser)
Small, elongated muscle;
lies inferior to infraspinatus
and may be inseparable
from that muscle; a rotator
cuff muscle
O—lateral border of
dorsal scapular surface
I—greater tubercle of
humerus inferior to
infraspinatus insertion
Same action(s) as
infraspinatus muscle
Axillary nerve
Teres major
Thick, rounded muscle;
located inferior to teres
minor; helps form posterior
wall of axilla (along
with latissimus dorsi and
subscapularis)
O—posterior surface of
scapula at inferior angle
I—crest of lesser tubercle
on anterior humerus;
insertion tendon fused
with that of latissimus
dorsi
Extends, medially rotates,
and adducts humerus
;
synergist of latissimus
dorsi
Lower subscapular
nerve (C
6
and C
7
)
Coracobrachialis
(kor
0
ah-ko-bra
0
ke-al
9
is)
(
coraco
5
coracoid;
brachi
5
arm)
Small, cylindrical muscle
O—coracoid process of
scapula
I — medial surface of
humerus shaft
Flexes and adducts
humerus
; synergist of
pectoralis major
Musculocutaneous
nerve (C
5
–C
7
)
*Rotator cuff muscles
MUSCLE GALLERY
Table 10.9
Muscles Crossing the Shoulder Joint: Movements of the Arm (Humerus)
(Figure 10.15)
(continued)
Long head
Biceps
brachii
Short head
O = origin
Ι
= insertion
(c)
O
O
Ι
O
O
Ι
Ι
Subscapularis*
Coracobrachialis
Brachialis
(d)
Figure 10.15
(continued)
Muscles crossing the shoulder and elbow joints, causing
movements of the arm and forearm, respectively.
(c)
The isolated biceps brachii muscle of
the anterior arm.
(d)
The brachialis muscle and the coracobrachialis and subscapularis muscles
shown in isolation in the diagram on the left, and in a dissection on the right.
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