The muscles of the arm have three functions: flex-
ing the forearm, extending the forearm, and rotating the
forearm. The biceps brachii, brachialis, and brachioradialis
flex the forearm. The triceps brachii extends the forearm.
The muscles responsible for the rotation of the forearm are
the supinator and the pronator teres. Figure 6.21 illustrates
and describes these muscles.
The two functions of the muscles of the forearm are
moving the wrist and moving the hand and fingers. The
flexor carpi radialis, flexor carpi ulnaris, extensor carpi
radialis longus, and extensor carpi ulnaris are all involved
in the wrist motion required to toss a Frisbee. The muscles
that let you grasp an object with your hand or move your
fingers to play the piano include the palmaris longus, flex-
or digitorum superficialis, flexor digitorum profundus, and
extensor digitorum. Figure 6.22 illustrates all of these
muscles and includes descriptions of their origins, inser-
tions, and actions.
M uscles o f th e arm th a t m ove th e radius and ulna • Figure 6.21
Humerus
Scapula
Humerus
Deltoid (cut)
Biceps brachii
Long head
Short head
Brachialis
Radius
Medial head
— Teres major
\
OD
a
Triceps brachii:
._—■—
’ ’
___ *
- Long head ------ '
' Lateral head —
\
u ' 4 , /
Ulna
Radius
Ulna
Muscle
Origin
Insertion
Action
Muscles of the arm
Biceps brachii
(BÏ-ceps BRÀ-kë-ï)
Scapula
Radius
Flexes and supinates forearm at elbow
joint; flexes arm at shoulder joint
Brachialis
(brâ'-kê-À-Ms)
Humerus
Ulna
Flexes forearm at elbow joint
Brachioradialis
(brà'-ke-ô-rà'-dë-À-Ms)
Humerus
Radius
Flexes forearm at elbow joint
Triceps brachii
(TRfceps BRÀ-ke-Ï)
Scapula and humerus
Ulna
Extends forearm at elbow joint; extends
arm at shoulder joint
Supinator
(SOO-pi-na-tor)
Humerus and ulna
Radius
Supinates forearm
Pronator teres
(PRO-na-tor TE-rez)
Humerus and ulna
Radius
Pronates forearm
180 CHAPTER 6
The Muscular System
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