10
The Muscular System:
Part C
Muscles Crossing the Shoulder Joint
• Nine muscles cross the shoulder joint to insert on and move the
humerus
Muscles Crossing the Shoulder Joint
• Some originate off the scapula; others originate off the axial
skeleton
• Three are prime movers of the arm
• Pectoralis major
• Latissimus dorsi
• Deltoid
• Actions include flexion, extension, adduction, abduction, and
rotation of humerus
Muscles Crossing the Shoulder Joint
Muscles Crossing the Shoulder Joint
• Four muscles are rotator cuff muscles
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Supraspinatus
Infraspinatus
Teres minor
Subscapularis
• Reinforce the capsule of the shoulder
• Act as synergists and fixators
• Two additional muscles are synergists: coracobrachialis and teres major
Muscles Crossing the Shoulder Joint
Rotator Cuff Anatomy and Function
Rotator Cuff Anatomy and Function
Rotator Cuff Anatomy and Function
Movement at the Glenohumeral Joint
Muscles Crossing the Elbow Joint
• Anterior flexor muscles
• Brachialis and biceps brachii—chief forearm flexors
• Brachioradialis—synergist and stabilizer
Muscles Crossing the Elbow Joint
Muscles Crossing the Elbow Joint
• Posterior extensor muscles
• Triceps brachii—prime mover of forearm extension
• Anconeus—weak synergist
Muscles Crossing the Elbow Joint
Muscles of the Forearm
• Actions: movements of the wrist, hand, and fingers
• Most anterior muscles are flexors and insert via the flexor
retinaculum
• Most posterior muscles are extensors and insert via the
extensor retinaculum
Muscles of the Forearm
• Some forearm muscles act to produce pronation and supination
of the forearm
Muscles of the Forearm
• Pronators: pronator teres and pronator quadratus
• Supinator: a synergist with the biceps brachii
Muscles of the Forearm: Anterior Compartment
• Flexors
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Flexor carpi radialis
Palmaris longus
Flexor carpi ulnaris
Flexor digitorum muscles (superficialis and profundus)
Flexor pollicis longus
Muscles of the Forearm: Anterior Compartment
Muscles of the Forearm: Anterior Compartment
Muscles of the Forearm: Posterior Compartment
• Extensors
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Extensor carpi radialis longus and brevis
Extensor digitorum
Extensor carpi ulnaris
Extensor pollicis brevis and longus
Extensor indicis
Abductor pollicis longus
Muscles of the Forearm: Posterior Compartment
Muscles of the Forearm: Posterior Compartment
Movements of the Wrist and Fingers
• Flexion and extension
• Abduction and adduction
Intrinsic Muscles of the Hand
• Small weak muscles
• Lie entirely within the palm of the hand
• Control precise movements of metacarpals and fingers (e.g.,
threading a needle)
• Abductors and adductors of the fingers
• Produce opposition—move the thumb toward the little finger
Finger and Thumb Movements
• Flexion
• Thumb—bends medially along the palm
• Fingers—bend anteriorly
• Extension
• Thumb—points laterally
• Fingers—move posteriorly
Intrinsic Muscles of the Hand
• Three groups
• Thenar eminence (ball of the thumb)
• Hypothenar eminence (ball of the little finger)
• Each of the above groups has a flexor, an abductor, and an opponens
muscle
• Midpalmar muscles: lumbricals and palmar and dorsal interossei extend
the fingers
• Interossei muscles also abduct and adduct the fingers
Intrinsic Muscles of the Hand