356
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
Pronator quadratus
(kwod-ra
9
tus) (
quad
5
square, four-sided)
Deepest muscle of distal
forearm; passes downward
and laterally; only muscle
that arises solely from
ulna and inserts solely into
radius
O—distal portion of
anterior ulnar shaft
I—distal surface of
anterior radius
Prime mover of forearm
pronation
; acts with
pronator teres; also helps
hold ulna and radius
together
Median nerve
(C
8
and T
1
)
PART II: POSTERIOR
MUSCLES
(Figure 10.17)
These muscles of the posterior fascial compartment are listed from the lateral to the medial aspect. They are all
innervated by the radial nerve or its branches. More than half of the posterior compartment muscles arise from
a common extensor origin tendon attached to the posterior surface of the lateral epicondyle of the humerus
and adjacent fascia. The extensor tendons are held in place at the posterior aspect of the wrist by the
extensor
retinaculum,
which prevents “bowstringing” of these tendons when the wrist is hyperextended. The
extensor
muscles of the fingers end in a broad hood over the dorsal side of the digits, the extensor expansion.
Superficial Muscles
Brachioradialis
(see Table 10.10)
See Table 10.10
See Table 10.10
See Table 10.10
See Table 10.10
Extensor carpi radialis
longus
(ek-sten
9
sor)
(
extend
5
increase angle
between two bones)
Parallels brachioradialis on
lateral forearm, and may
blend with it
O—lateral supracondylar
ridge of humerus
I—base of second
metacarpal
Extends wrist
in
conjunction with extensor
carpi ulnaris and
abducts
wrist
in conjunction with
flexor carpi radialis
Radial nerve
(C
6
and C
7
)
Extensor carpi radialis brevis
(bre
˘
9
vis)
(
brevis
5
short)
Shorter than extensor carpi
radialis longus and lies
deep to it
O—lateral epicondyle of
humerus
I—base of third
metacarpal
Extends and abducts
wrist
; acts synergistically
with extensor carpi
radialis longus to steady
wrist during finger
flexion
Deep branch of radial
nerve
Extensor digitorum
Lies medial to extensor
carpi radialis brevis; a
detached portion of this
muscle, called
extensor
digiti minimi,
extends little
finger
O—lateral epicondyle of
humerus
I—by four tendons into
extensor expansions
and distal phalanges of
fingers 2–5
Prime mover of finger
extension
; extends wrist;
can abduct (flare) fingers
Posterior interosseous
nerve, a branch
of radial nerve
(C
5
and C
6
)
Extensor carpi ulnaris
Most medial of superficial
posterior muscles; long,
slender muscle
O—lateral epicondyle of
humerus and posterior
border of ulna
I—base of fifth
metacarpal
Extends wrist
in
conjunction with extensor
carpi radialis and
adducts
wrist
in conjunction with
flexor carpi ulnaris
Posterior interosseous
nerve
Deep Muscles
Supinator
(soo
0
pı˘-na
9
tor)
(
supination
5
turning palm
anteriorly or upward)
Deep muscle at posterior
aspect of elbow; largely
concealed by superficial
muscles
O—lateral epicondyle of
humerus; proximal ulna
I—proximal end of radius
Assists biceps brachii to
forcibly supinate forearm
;
works alone in slow
supination; antagonist of
pronator muscles
Posterior interosseous
nerve
Abductor pollicis longus
(ab-duk
9
tor)
(
abduct
5
movement away
from median plane)
Lateral and parallel to
extensor pollicis longus; just
distal to supinator
O—posterior surface
of radius and ulna;
interosseous membrane
I—base of first
metacarpal and
trapezium
Abducts and extends
thumb
Posterior interosseous
nerve
Extensor pollicis brevis and
longus
Deep muscle pair with a
common origin and action;
overlain by extensor carpi
ulnaris
O—dorsal shaft of radius
and ulna; interosseous
membrane
I—base of proximal
(brevis) and distal
(longus) phalanx of
thumb
Extends thumb
Posterior interosseous
nerve
MUSCLE GALLERY
Table 10.11
Muscles of the Forearm: Movements of the Wrist, Hand,
and Fingers
(Figures 10.16 and 10.17)
(continued)
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