Muscular System Part 2

• Intrinsic muscles of the shoulder


  Muscles that originate and insert on the scapula and humerus

  
• Lateral intrinsic shoulder muscles

  • Deltoideus
  • Infraspinatus
  • Teres minor
  • Supraspinatus

  
• Deltoideus


  Muscle with 2 portions that flexes the shoulder

  
• Deltoideus


  • Origin: The spine and acromial process of the scapula
  • Insertion: The deltoid tuberosity
  • Innervation: Axillary nerve
• Infraspinatus


  • Origin: The infraspinous fossa
  • Insertion: A small, circumscribed area on the lateral side of the greater tubercle of the humerus
  • Action: To extend or flex the joint, depending on the degree of extension or position of the joint when the muscle contracts. To abduct the shoulder and to rotate the arm laterally.
  • Innervation: Suprascapular nerve

  
• Teres minor


  • Origin: The infragleonoid tubercle and distal third of the caudal border of the scapula
  • Insertion: The teres minor tuberosity of the humerus
  • Action: To flex the shoulder and rotate the arm laterally
  • Innervation: Axillary nerve

  
• Supraspinatus


  • Origin: The supaspinous fossa
  • Insertion: The greater tubercle of the humerus, by a thick tendon
  • Action: To extend the shoulder
  • Innervation: Suprascapular nerve

  
• Medial intrinsic shoulder muscles

  • Subscapularis
  • Teres major
  • Coracobrachialis

  
• Subscapularis


  • Origin: The subscapular fossa
  • Insertion: The lesser tubercle of the humerus
  • Action: To adduct and extend the shoulder
  • Innervation: Subscapular nerve
• Teres major


  • Origin: The caudal angle and adjacent border of the scapula; the caudal surface of the subscapularis
  • Insertion: The teres major tuberosity of the humerus
  • Action: Flex the shoulder and rotate the arm medially
  • Innervation: Axillary nerve

  
• Coracobrachialis


  • Origin: The coracoid process of the scapula
  • Insertion: The crest of the lesser tubercle of the humerus proximal to the teres major tuberosity
  • Action: To adduct and extend the shoulder
  • Innervation: Musculocutaneous nerve

  
• Caudal muscles of the forearm

  • Tensor fascia antebrachii
  • Triceps brachii (long, lateral, medial, accessory heads)
  • Anconeus

  
• Tensor fascia antebrachii


  • Origin: The fascia covering the lateral side of the latissimus dorsi
  • Insertion: The olecranon
  • Action: To extend the elbow
  • Innervation: Radial nerve
• Triceps brachii (long head)

  • Origin: the caudal border of the scapula
  • Insertion: The olecranon
  • Action: To extend the elbow and flex the shoulder
  • Innervation: Radial nerve

  
• Triceps brachii (lateral head)

  • Origin: laterally on humerus; crest of the greater tubercle of the humerus
  • Insertion: The olecranon
  • Action: To extend the elbow
  • Innervation: Radial nerve
• Triceps brachii (medial head)


  • Origin: medially on humerus; caudal tuberosity of teres major, crest of the lesser tubercle
  • Insertion: The olecranon
  • Action: To extend the elbow
  • Innervation: Radial nerve

  
• Triceps brachii (accessory head)


  • Origin: The neck of the humerus
  • Insertion: The olecranon
  • Action: To extend the elbow
  • Innervation: Radial nerve
• Anconeus


  • Origin: The lateral epicondylar crest and the lateral and medial epicondyles of the humerus
  • Insertion: The lateral surface of the proximal end of the ulna
  • Action: To extend the elbow
  • Innervation: Radial nerve
• Cranial muscles of the forearm

  • Biceps brachii
  • Brachialis

  
• Biceps brachii


  • Origin: The supraglenoid tubercle
  • Insertion: The ulnar and radial tuberosities
  • Action: To flex the elbow and extend the shoulder
  • Innervation: Musculocutaneous nerve

  
• Brachialis


  • Origin: The proximal third of the lateral surface of the humerus
  • Insertion: The ulnar and radial tuberosities
  • Action: To flex the elbow
  • Innervation: Musculocutaneous nerve

  
• Caudal/Medial and Cranial/Lateral muscles of the forearm

  • Extensor carpi radialis
  • Common digital extensor
  • Lateral digital extensor
  • Ulnaris lateralis
  • Supinator
  • Pronator teres
  • Abductor pollicis longus
  • Flexor carpi radialis
  • Superficial digital flexor
  • Flexor carpi ulnaris
  • Deep digital flexor
  • Pronator quadratus

  
• Extensor carpi radialis


  • Origin: The lateral epicondylar crest
  • Insertion: The small tuberosities on the proximal ends and dorsal surfaces of metacarpals II and III
  • Action: To extend the carpus
  • Innervation: Radial nerve
• Common digital extensor


  • Origin: The lateral epicondyle of the humerus
  • Insertion: The extensor processes of the distal phalanges of digits II, III, IV and V
  • Action: To extend the joints of the 4 principal digits
  • Innervation: Radial nerve

  
• Lateral digital extensor


  • Origin: The lateral epicondyle of the humerus
  • Insertion: The proximal ends of all phalanges of digits III, IV, and V, but mainly the extensor processes of the distal phalanges of these digits
  • Action: To extend the joints of digits III, IV, and V
  • Innervation: Radial nerve
• Ulnaris lateralis


  • Origin: the lateral epicondyle of the humerus
  • Insertion: the lateral aspect of the proximal end of metacarpal V and the accessory carpal bone
  • Action: To abduct and flex the carpus
  • Innervation: Radial nerve

  
• Supinator


  • Origin: The lateral epicondyle of the humerus
  • Insertion: The crania; surface of the proximal fourth of the radius
  • Action: To rotate the forearm laterally so that the palmar side of the paw faces medially (supination), and to flex the elbow
  • Innervation: Radial nerve

  
• Pronator teres


  • Origin: The medial epicondyle of the humerus
  • Insertion: The medial border of the radius between the proximal and middle thirds
  • Action: To rotate the forearm medially so that the palmar side of the paw faces the ground (pronation); to flex the elbow
  • Innervation: Median nerve

  
• Abductor pollicis longus


  • Origin: The lateral border and cranial surface of the body of the ulna; the interosseous membrane
  • Insertion: The proximal end of metacarpal I
  • Action: To abduct the first digit or pollex
  • Innervation: Radial nerve
• Flexor carpi radialis


  • Origin: The medial epicondyle of the humerus and the medial border of the radius
  • Insertion: The palmar side of the proximal ends of metacarpals II and III
  • Action: To flex the carpus
  • Innervation: Median nerve

  
• Superficial digital flexor


  • Origin: The medial epicondyle of the humerus
  • Insertion: The palmar surface of the base (proximal end) of the middle phalanges of digits II, III, IV and V
  • Action: To flex digits II, III, IV and V
  • Innervation: Median nerve

  
• Flexor carpi ulnaris


  • Origin: Ulnar head – the caudal border and medial surface of the olecranon; humeral head – the medial epicondyle of the humerus
  • Insertion: the accessory carpal bone
  • Action: to flex the carpus
  • Innervation: ulnar nerve

  
• Deep digital flexor


  • Origin: Humeral head – the medial epicondyle of the humerus, Ulnar head – the proximal three-fourths of the caudal border of the ulna, Radial head – the middle third of the medial border of the radius
  • Insertion: the palmar surface of the base (proximal end) of the distal phalanx of each digit
  • Action: to flex the digit
  • Innervation: median and ulnar nerves

  
• Pronator quadratus


  • Attachments: the apposed surfaces of the radius and the ulna
  • Action: to pronate the paw
  • Innervation: median nerve