Superficial and Deep Back Muscles

• Attachments shaded in green will be on the test

Superficial Back Muscles

• Trapezius originates at the external occipital protuberance and spines of C7-T12
• Trapezius inserts on the clavicle, acromion, and spine of the scapula
• Trapezius is innervated by the Accessory nerve (CN XI)
• Contraction of the trapezius elevates, adducts/retracts, depresses, and rotates the glenoid superiorly
• Latissimus dorsi originates on the inferior 6 thoracic processes, thoracolumbar fascia, and iliac crest
• Latissimus dorsi inserts on the intertubercular sulcus
• The thoracodorsal nerve innervates the latissimus dorsi
• Latissimus dorsi extends, adducts, and medially rotates the humerus

Deep Back Muscles

• The levator scapulae originates at the transverse processes of C1-C4
• Levator scapulae inserts on the superior angle of the scapula
• Levator scapulae elevates and rotates the glenoid inferiorly
• The rhomboid minor originates at the spines of C7-T1
• Rhomboid minor inserts on the medial scapular border superior to the scapular spine
• The dorsal scapular nerve innervates the rhomboid minor
• Rhomboid Minor retracts and rotates glenoid inferiorly
• Rhomboid major originates at the spines of T2-T5
• Rhomboid major inserts on the medial scapular border inferior to the scapular spine
• Rhomboid Major retracts and rotates glenoid inferiorly

Intrinsic Back Muscles

• Splenius originates on the nuchal ligament and spinous processes of C7-T6
• Splenius inserts on the mastoid process and superior nuchal line of the cervical vertebrae
• Posterior rami of spinal nerves innervate the splenius
• Unilateral contraction of the splenius laterally flexes the neck and rotates the head ipsilaterally
• Bilateral contraction of the splenius extends the head and neck
• Iliocostalis, Longissimus, & Spinalis originate at the iliac crest, posterior sacrum, surface, and lumbar vertebrae
• Erector spinae inserts superiorly to the ribs and vertebral transverse and spinous processes
• Posterior rami of spinal nerves innervate the erector spinae
• Unilateral contraction of the erector spinae laterally flexes the vertebral column
• Bilateral contraction of the erector spinae extends the vertebral column and head
• Transversospinalis originates at the sacrum and transverse processes of all vertebrae
• Transversospinalis inserts on the occipital bone and spinous process superior to the origin
• Posterior rami of spinal nerves innervate the transversospinalis
• Transversospinalis extends head, thoracic, and cervical regions of vertebral column, and contralaterally rotates them

Shoulder Muscles

• Deltoid originates on the clavicle, acromion, and spine of the scapula
• Deltoid inserts on the deltoid tuberosity
• The axillary nerve (C5-C6) innervates the deltoid
• Anterior part of the deltoid flexes and medially rotates the arm
• Middle part of the deltoid abducts the arm 15-90°
• Posterior part of the deltoid extends and laterally rotates the arm
• Teres major originates at the inferior angle of scapula
• Teres major inserts on the intertubercular sulcus
• The lower subscapular nerve innervates the teres major
• Contraction extends the arm and assists in adduction and medial rotation of the arm
• Supraspinatus originates at the supraspinous fossa of the scapula
• Supraspinatus abducts the arm 0-15°
• The suprascapular nerve innervates the supraspinatus
• Infraspinatus originates at the infraspinous fossa of the scapula and inserts on the greater tubercle
• Infraspinatus laterally rotates the arm
• Teres minor originates at the lateral border of the scapula
• The axillary nerve innervates the teres minor
• Teres minor laterally rotates and extends the arm
• Subscapularis originates at the subscapular fossa
• Subscapularis inserts on the lesser tubercle
• Upper and lower subscapular nerves innervate the subscapularis
• Action of the subscapularis is to medially rotate the arm

Pectoral Region Muscles

• Pectoralis major has two heads: clavicular originating from the medial clavicle and sternocostal originating from the sternum and superior six costal cartilages
• Pectoralis major inserts on the intertubercular sulcus
• Medial and lateral pectoral nerves innervate the pectoralis major
• The whole pectoralis major adducts and medially rotates the arm
• The clavicular part flexes the arm while sternocostal extends the arm from a flexed position
• Pectoralis minor originates on the 3rd-5th ribs
• Pectoralis minor inserts on the scapular coracoid process
• The medial pectoral nerve innervates the pectoralis minor
• Contraction stabilizes the scapula against the thoracic wall
• Serratus anterior originates on the 1st-9th ribs
• Serratus anterior inserts on the vertebral border of the scapula
• The long thoracic nerve innervates the serratus anterior
• Serratus anterior protracts the scapula and rotates it upwards

Arm Muscles - Posterior

• Triceps brachii has a long head originating from the infraglenoid tubercle, a lateral head originating proximal to the radial groove, and a medial head originating distal to the radial groove
• Triceps brachii has a common insertion on the olecranon process
• The radial nerve innervates the triceps brachii
• Triceps brachii is the main forearm extensor

Arm Muscles - Anterior

• Biceps brachii has a short head originating from the scapular coracoid process and a long head originating from the supraglenoid tubercle
• Biceps brachii inserts on the radial tuberosity
• Biceps brachii supinates the forearm, flexes the forearm, and assists arm flexion
• Coracobrachialis originates from the scapular coracoid process
• Coracobrachialis inserts on the medial humeral diaphysis
• Musculocutaneous nerve innervates coracobrachialis
• Coracobrachialis helps flex and adduct the arm
• Brachialis originates from the distal humerus and inserts on the ulnar coronoid process and tuberosity
• Brachialis flexes the forearm in all positions

Forearm Muscles - Anterior

• Pronator teres has ulnar and humeral heads
• Ulnar head originates at the coronoid process
• Humeral head originates at the medial humeral epicondyle
• Pronator teres inserts on the middle of the radius
• Pronator teres is innervated by the median nerve
• Pronator teres pronates and flexes the forearm
• Flexor carpi radialis originates at the medial humeral epicondyle and inserts on the 2nd metacarpal
• Flexor carpi radialis is innervated by the median nerve
• Flexor carpi radialis flexes and abducts the hand at the wrist
• Palmaris longus originates at the medial humeral epicondyle and inserts on the palmar aponeurosis
• Palmaris longus flexes the hand at the wrist and tenses the palmar aponeurosis
• Flexor carpi ulnaris originates at the medial humeral epicondyle, olecranon, and posterior ulna
• Flexor carpi ulnaris inserts on the medial carpals and 5th metacarpal
• The ulnar nerve innervates the flexor carpi ulnaris
• Flexor carpi ulnaris flexes and adducts the hand at the wrist
• Flexor digitorum superficialis originates at the medial humeral epicondyle, ulnar coronoid process, and proximal radius
• Flexor digitorum superficialis inserts on the 2nd-5th middle phalanges
• The median nerve innervates the flexor digitorum superficialis
• Flexor digitorum superficialis flexes digits 2-5
• Flexor digitorum profundus originates from the proximal ulna and interosseous membrane and inserts on the 2nd-5th distal phalanges
• Medial part of the flexor digitorum profundus is innervated by the ulnar nerve
• Lateral part of the flexor digitorum profundus is innervated by the median nerve.
• Flexor digitorum profundus flexes 2nd-5th distal phalanges
• Flexor pollicis longus originates at the anterior radius and interosseous membrane
• Flexor pollicis longus inserts on the base of the 1st distal phalanx
• The median nerve innervates the flexor pollicis longus
• Pronator quadratus originates at the distal anterior ulnar surface
• Pronator quadratus inserts on the distal radial shaft
• The median nerve innervates the pronator quadratus
• Action of the pronator quadratus is to pronate the forearm

Forearm Muscles - Posterior

• Brachioradialis originates at the supracondylar ridge of the humerus
• Brachioradialis inserts on the radial styloid process
• Brachioradialis weakly flexes the forearm best when the forearm is midpronated
• Extensor carpi radialis longus originates at the supracondylar ridge of the humerus and inserts on the 2nd metacarpal
• Extensor carpi radialis brevis originates at the lateral humeral epicondyle and inserts on the 3rd metacarpal
• Radial nerve innervates extensor carpi radialis longus and brevis
• These muscles extend and abduct the hand at the wrist.
• Extensor digitorum originates at the lateral humeral epicondyle and inserts on the posterior digits 2-5
• The radial nerve innervates the extensor digitorum
• Extensor digitorum extends digits 2-5
• Extensor digiti minimi originates at the lateral humeral epicondyle and inserts on the posterior digit 5
• The radial nerve innervates the extensor digiti minimi
• Extensor digiti minimi extends digit 5
• Extensor carpi ulnaris originates at the lateral humeral epicondyle and posterior ulna
• Extensor carpi ulnaris inserts on the 5th metacarpal
• The radial nerve innervates the extensor carpi ulnaris
• Extensor carpi ulnaris extends and adducts the wrist
• Abductor pollicis longus originates at the proximal ulna, radius, and interosseous membrane and inserts on the 1st metacarpal
• Extensor pollicis brevis originates at the mid-posterior radial surface and interosseous membrane and inserts on the 1st proximal phalanx
• Extensor pollicis longus originates at the mid-posterior ulnar surface and interosseous membrane and inserts on the 1st distal phalanx
• The radial nerve innervates all three muscles
• Abductor pollicis longus abducts and extends digit 1 at the wrist
• Extensor pollicis brevis extends digit 1 at the wrist
• Extensor pollicis longus extends digit 1 at the wrist
• Extensor indicis originates at the distal ulna and interosseous membrane and inserts on the posterior digit 2
• The radial nerve innervates the extensor indicis
• Extensor indicis extends digit 2 (independently) and helps extend the hand at the wrist
• Supinator originates at the lateral humeral epicondyle and supinator crest of the ulna and inserts on the proximal 1/3 of the lateral radius
• The radial nerve innervates the supinator
• The supinator supinates the forearm

Hand Muscles

• Thenar muscles originate at the lateral carpals and insert on the 1st proximal phalanx
• The median nerve innervates the thenar muscles
• Thenar muscles flex, abduct, and oppose the thumb
• Adductor pollicis originates at the oblique head (2nd and 3rd MC) and transverse head (3rd MC), and inserts on the 1st proximal phalanx
• Adductor pollicis adducts the thumb
• Hypothenar muscles originate at the pisiform and hamate and insert on the 5th proximal phalanx
• The ulnar nerve innervates the hypothenar muscles
• Hypothenar muscles abduct and flex digit 5