316
UNIT TWO
a person turns a doorknob or screwdriver (see f g. 9.31).
The
brachialis
(bra
ke-al-is) is a large muscle beneath
the biceps brachii. It connects the shaFt oF the humerus to the
ulna and is the strongest fl
exor oF the elbow (see f
g. 9.31).
The
brachioradialis
(bra
ke-o-ra
de-a
lis) connects
the humerus to the radius. It aids in fl
exing the elbow (see
f
g. 9.32).
Extensor
The
triceps brachii
(tri
seps bra
ke-i) has three heads and
is the only muscle on the back oF the arm. It connects the
humerus and scapula to the ulna and is the primary extensor
oF the elbow (see f
gs. 9.29 and 9.30).
Rotators
The
supinator
(su
pı˘-na-tor) is a short muscle whose f
bers
run From the ulna and the lateral end oF the humerus to the
radius. It assists the biceps brachii in rotating the Forearm
laterally, as when the hand is turned so the palm is Facing
upward (supination) (see f
g. 9.32).
The
pronator teres
(pro-na
tor te
re
¯z) is a short muscle
connecting the ends oF the humerus and ulna to the radius. It
rotates the arm medially, as when the hand is turned so the
palm is Facing downward (pronation) (see f
g. 9.32).
The
pronator quadratus
(pro-na
tor kwod-ra
tus) runs
From the distal end oF the ulna to the distal end oF the radius.
It assists the pronator teres in rotating the arm medially (see
f
g. 9.32).
Muscles That Move the Hand
Movements oF the hand include movements oF the wrist
and f
ngers. Many oF the implicated muscles originate From
the distal end oF the humerus and From the radius and
ulna. The two major groups oF these muscles are fl
exors on
the anterior side oF the Forearm and extensors on the pos-
terior side. ±igures 9.32, 9.33, 9.34, reFerence plate 70, and
Rotators
The
subscapularis
(sub-scap
u-lar-is) is a large, triangular
muscle that covers the anterior surFace oF the scapula. It con-
nects the scapula to the humerus and rotates the arm medi-
ally (see f
g. 9.31).
The
infraspinatus
(in
Frah-spi
na-tus) occupies the
depression below the spine oF the scapula on its posterior
surFace. The f
bers oF this muscle attach the scapula to the
humerus and rotate the arm laterally (see f
g. 9.29).
The
teres minor
is a small muscle connecting the scap-
ula to the humerus. It rotates the arm laterally (see f
gs. 9.27
and 9.29).
Muscles That Move the Forearm
Most Forearm movements are produced by muscles that con-
nect the radius or ulna to the humerus or pectoral girdle. A
group oF muscles located along the anterior surFace oF the
humerus fl exes the Forearm at the elbow, whereas a single
posterior muscle extends this joint. Other muscles cause
movements at the radioulnar joint and rotate the Forearm.
The muscles that move the Forearm are shown in
f
gures
9.31,
9.32, 9.33
, and
9.34,
in reFerence plates 68, 69, and 70,
and are listed in
table 9.8
, grouped according to their pri-
mary actions. They include the Following:
Flexors
Extensor
Rotators
Biceps brachii
Triceps brachii
Supinator
Brachialis
Pronator teres
Brachioradialis
Pronator
quadratus
Flexors
The
biceps brachii
(bi
seps bra
ke-i) is a Fleshy muscle
that Forms a long, rounded mass on the anterior side oF the
arm. It connects the scapula to the radius and fl
exes the
elbow and rotates the hand laterally (supination), as when
TABLE
9.8
|
Muscles That Move the Forearm
Muscle
Origin
Insertion
Action
Nerve Supply
Biceps brachii
Coracoid process and tubercle above
glenoid cavity of scapula
Radial tuberosity of radius
Flexes elbow and rotates
hand laterally
Musculocutaneous n.
Brachialis
Anterior shaft of humerus
Coronoid process of ulna
Flexes elbow
Musculocutaneous, median,
and radial nerves
Brachioradialis
Distal lateral end of humerus
Lateral surface of radius above
styloid process
Flexes elbow
Radial n.
Triceps brachii
Tubercle below glenoid cavity and lateral
and medial surfaces of humerus
Olecranon process of ulna
Extends elbow
Radial n.
Supinator
Lateral epicondyle of humerus and crest
of ulna
Lateral surface of radius
Rotates forearm laterally and
supinates hand
Radial n.
Pronator teres
Medial epicondyle of humerus and
coronoid process of ulna
Lateral surface of radius
Rotates forearm medially and
pronates hand
Median n.
Pronator quadratus
Anterior distal end of ulna
Anterior distal end of radius
Rotates forearm medially and
pronates hand
Median n.
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