HUMAN BIOLOGY

the MUSCULar SYSteM 105

Figure 6.2 Some of the major muscles of the muscular system. (© Cengage Learning)

Triceps brachii
Straightens
the forearm
at elbow

Deltoid

Raises the arm

Trapezius

Lifts the shoulder blade,

braces the shoulder,

draws the head back

Latissimus dorsi

Rotates and draws the

arm backward and

toward the body

Gluteus maximus

Extends and rotates the

thigh outward when

walking, running, and

climbing

Biceps femoris

(Hamstring muscle)

Draws thigh backward,

bends the knee

Pectoralis major
Draws the arm forward
and in toward the body

Serratus anterior
Draws shoulder blade
forward, helps raise arm,
assists in pushes

External oblique
Compresses the abdomen,
assists in lateral rotation
of the trunk

Rectus abdominis
Depresses the thoracic
(chest) cavity, compresses
the abdomen, bends the
backbone

Adductor longus
Flexes, laterally rotates,
and draws the thighs
toward the body

Sartorius
Bends the thigh at the hip,
bends lower leg at the
knee, rotates the thigh in
an outward direction

Gastrocnemius

Bends the lower leg at

the knee when walking,

extends the foot when

jumping

Quadriceps femoris
Flexes the thigh at hips,
extends the leg at the knee

Tibialis anterior
Flexes the foot toward
the shin

Biceps brachii

Bends the forearm at

the elbow

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