2 Musculature: Functional Groups
2.1 Functional Muscle Groups
A Principles used in classification of the muscles of the upper limb
The muscles of the upper limb can be classified according to various criteria. An optimum system for classification should be logical and clear. The following criteria are suitable for classifying muscles:
• Origin
• Topography
• Func tion
• Innervation
While function and topography in the upper limb are often interrelated (muscles with the same action on a joint are often located close together), muscles that have similar actions in the shoulder region (e.g., muscles of the shoulder joint and shoulder girdle) vary considerably in their location. The following classification (B), then, is a compromise between topographical and functional considerations. In section C, a different muscle classification system, based on innervation, is presented.
The grouping of muscles by the pattern of their innervation reveals features of their embryological and phylogenetic origin and provides clinical insights into the clusters of consequences from damage to particular nerves.
B Functional-topographical classification of the muscles of the upper limb
Muscles of the shoulder girdle |
Shoulder girdle muscles that have migrated from the head • Trapezius • Sternocleidomastoid • Omohyoid Posterior muscles of the trunk and shoulder girdle • Rhomboid major • Rhomboid minor • Levator scapulae Anterior muscles of the trunk and shoulder girdle • Subclavius • Pectoralis minor • Serratus anterior |
Muscles of the shoulder joint |
Posterior shoulder muscles • Supraspinatus • Infraspinatus • Teres minor • Subscapularis • Deltoid • Latissimus dorsi • Teres major Anterior shoulder muscles • Pectoralis major • Coracobrachialis |
Muscles of the arm |
Posterior arm muscles • Triceps brachii • Anconeus Anterior arm muscles • Brachialis • Biceps brachii |
Muscles of the forearm |
Posterior forearm muscles • Superficial extensors – Extensor digitorum – Extensor digiti minimi – Extensor carpi ulnaris • Deep extensors – Supinator – Abductor pollicis longus – Extensor pollicis brevis – Extensor pollicis longus – Extensor indicis Anterior forearm muscles • Superficial flexors – Pronator teres – Flexor digitorum superficialis – Flexor carpi radialis – Flexor carpi ulnaris – Palmaris longus • Deep flexors – Flexor digitorum profundus – Flexor pollicis longus – Pronator quadratus Radial forearm muscles • Radialis group – Brachioradialis – Extensor carpi radialis longus – Extensor carpi radialis brevis |
Muscles of the hand |
Metacarpal muscles • First through fourth lumbricals • First through fourth dorsal interossei • First through third palmar interossei Thenar muscles • Abductor pollicis brevis • Adductor pollicis • Flexor pollicis brevis • Opponens pollicis Hypothenar muscles • Abductor digiti minimi • Flexor digiti minimi brevis • Opponens digiti minimi |
C Classification of the muscles of the upper limb by their innervation
Almost all the muscles of the upper limb are innervated by the brachial plexus arising from spinal cord segments C 5–T 1. Exceptions are the trapezius, sternocleidomastoid, and omohyoid; originating in vertebrate evolution as muscles of the head, they are supplied by cranial nerve XI (accessory nerve) and the cervical plexus (ansa cervicalis).
Nerve | Innervated muscles |
Accessory nerve | Trapezius Sternocleidomastoid |
Ansa cervicalis | Omohyoid |
Dorsal scapular nerve | Levator scapulae Rhomboid major Rhomboid minor |
Suprascapular nerve | Supraspinatus Infraspinatus |
Long thoracic nerve | Serratus anterior |
Nerve to the subclavius | Subclavius |
Subscapular nerves | Subscapularis (upper and lower) Teres major (upper) |
Thoracodorsal nerve | Latissimus dorsi |
Medial and lateral pectoral nerves | Pectoralis major Pectoralis minor |
Musculocutaneous nerve | Coracobrachialis Biceps brachii Brachialis |
Axillary nerve | Deltoid Teres minor |
Radial nerve | Triceps brachii Anconeus Supinator Brachioradialis Extensor carpi radialis longus Extensor carpi radialis brevis Extensor digitorum Extensor digiti minimi Extensor carpi ulnaris Extensor pollicis longus Extensor pollicis brevis Extensor indicis Abductor pollicis longus |
Median nerve | Pronator teres Pronator quadratus Palmaris longus Flexor carpi radialis Flexor pollicis longus Flexor digitorum profundus (half) Flexor digitorum superficialis Abductor pollicis brevis Opponens pollicis Flexor pollicis brevis (superficial head) First and second lumbricals |
Ulnar nerve | Flexor carpi ulnaris Flexor digitorum profundus (half) Palmaris brevis Flexor digiti minimi brevis Abductor digiti minimi Opponens digiti minimi Adductor pollicis Flexor pollicis brevis (deep head) Palmar and dorsal interossei Third and fourth lumbricals |
D Overview of the motor branches of the brachial plexus that supply the muscles of the upper limb
With the outgrowth of the limb buds from the trunk during embryonic development, the branches of the brachial plexus follow the genetically determined posterior extensor muscles and anterior flexor muscles. The nerves for the extensors (radial and axillary nerves) arise from the three posterior divisions of the brachial plexus, while the nerves for the flexors (musculocutaneous nerve, ulnar nerve, median nerve) arise from the three anterior divisions of the plexus (see p. 396, Neurovascular Systems: Topographical Anatomy).
2.2 The Muscles of the Shoulder Girdle: Trapezius, Sternocleidomastoid, and Omohyoid
A Schematic of the trapezius
Trapezius | |
Origin: | ① Descending part11: • Occipital bone (superior nuchal line and external occipital protuberance) • The spinous processes of all cervical vertebrae via the nuchal ligament ② Transverse part: Broad aponeurosis at the level of the T 1–T 4 spinous processes ③ Ascending part: Spinous processes of T 5–T 12 |
Insertion: | • Lateral third of the clavicle (descending part) • Acromion (transverse part) • Scapular spine (ascending part) |
Actions: | • Descending part: – Draws the scapula obliquely upward and rotates the glenoid cavity inferiorly (acting with the inferior part of the serratus anterior) – Tilts the head to the same side and rotates it to the opposite side (with the shoulder girdle fixed) • Transverse part: draws the scapula medially • Ascending part: draws the scapula medially downward (supports the rotating action of the descending part) • Entire muscle: steadies the scapula on the thorax |
Innervation: | Accessory nerve (CN XI) and cervical plexus (C2, C4) |
B Schematic of the sternocleidomastoid
Sternocleidomastoid | ||
Origin: | • Sternal head: manubrium • Clavicular head: medial third of the clavicle | |
Insertion: | Mastoid process and superior nuchal line | |
Actions: | • Unilateral: | – Tilts the head to the same side – Rotates the head to the opposite side |
| • Bilateral: | – Extends the head – Assists in respiration when the head is fixed |
Innervation: | Accessory nerve (CN XI) and the cervical plexus (C 2, C 3) | |
C Schematic of the omohyoid
Omohyoid | |
Origin: | Superior border of the scapula |
Insertion: | Body of the hyoid bone |
Actions: | • Depresses (fixes) the hyoid bone • Moves the larynx and hyoid bone downward (for phonation and the final phase of swallowing) • Tenses the cervical fascia with its intermediate tendon and maintains patency of the internal jugular vein |
Innervation: | Ansa cervicalis (C 1–C 3) from the cervical plexus |
1The tables and associated diagrams above are intended to give a systematic overview of the named muscles and their actions, while the drawings on p. 299 are intended to display the muscles as they would appear in a dissection. Not all structures listed in the tables are shown in the drawings on p. 299 because they are not all visible in those views.
D The trapezius
Posterior view.
E The sternocleidomastoid and omohyoid
Right side, lateral view.
F The omohyoid
Right side, anterior view.
2.3 The Muscles of the Shoulder Girdle: Serratus Anterior, Subclavius, Pectoralis Minor, Levator Scapulae, and Rhomboids Major and Minor
A Schematic of the serratus anterior
Serratus anterior | |
Origin: | First through ninth ribs |
Insertion: | Scapula: ① Superior part (costal and dorsal surfaces of superior angle) ② Intermediate part (costal surface of medial border) ③ Inferior part (costal and dorsal surfaces of inferior angle and costal surface of medial border) |
Actions: | • Entire muscle: draws the scapula laterally forward, elevates the ribs when the shoulder girdle is fixed (assists in respiration) • Inferior part: rotates the scapula and draws its inferior angle laterally forward (rotates glenoid cavity superiorly), allowing for arm to be elevated above 90° • Superior part: lowers the raised arm (antagonist to the inferior part) |
Innervation: | Long thoracic nerve (C5–C7) |
B Schematic of the subclavius and pectoralis minor
① Subclavius | |
Origin: | First rib (chondro-osseous junction) |
Insertion: | Inferior surface of the clavicle (lateral third) |
Action: | Steadies the clavicle in the sternoclavicular joint |
Innervation: | Nerve to the subclavius (C5, C6) |
② Pectoralis minor | |
Origin: | Third through fifth ribs |
Insertion: | Coracoid process of the scapula |
Actions: | • Draws the scapula downward, causing its inferior angle to move posteromedially (lowers the raised arm), rotates glenoid inferiorly • Assists in respiration |
Innervation: | Medial and lateral pectoral nerves (C8, T1) |
C Schematic of the levator scapulae and rhomboids minor and major
① Levator scapulae | |
Origin: | Transverse processes of the C1–C4 vertebrae |
Insertion: | Superior angle of the scapula |
Action: | • Draws the scapula medially upward while moving the inferior angle medially (returns the raised arm to the neutral [0°] position) • Inclines the neck toward the same side (when the scapula is fixed) |
Innervation: | Dorsal scapular nerve and cervical spinal nerves (C3, C4) |
② Rhomboid minor | |
Origin: | Spinous processes of the C6 and C7 vertebrae |
Insertion: | Medial border of the scapula (above the scapular spine) |
Actions: | • Steadies the scapula • Draws the scapula medially upward (returns the raised arm to the neutral [0°] position) |
Innervation: | Dorsal scapular nerve (C4, C5) |
③ Rhomboid major | |
Origin: | Spinous processes of the T 1–T 4 vertebrae |
Insertion: | Medial border of the scapula (below the scapular spine) |
Actions: | • Steadies the scapula • Draws the scapula medially upward (returns the raised arm to the neutral [0°] position) |
Innervation: | Dorsal scapular nerve (C4, C5) |
D The serratus anterior
Right side, lateral view.
E The pectoralis minor and subclavius
Right side, anterior view.
F The levator scapulae, rhomboid major, and rhomboid minor
Right side, posterior view.
2.4 The Posterior Muscles of the Shoulder Joint: The Rotator Cuff
A Schematic of the subscapularis
① Subscapularis | |
Origin: | Subscapular fossa of the scapula |
Insertion: | Lesser tubercle of the humerus |
Action: | Internal rotation |
Innervation: | Upper and lower subscapular nerves (C5, C6) |
B Schematic of the supraspinatus, infraspinatus, and teres minor
② Supraspinatus | |
Origin: | Supraspinous fossa of the scapula |
Insertion: | Greater tubercle of the humerus |
Action: | Abduction |
Innervation: | Suprascapular nerve (C4–C6) |
③ Infraspinatus | |
Origin: | Infraspinous fossa of the scapula |
Insertion: | Greater tubercle of the humerus |
Action: | External rotation |
Innervation: | Suprascapular nerve (C4–C6) |
④ Teres minor | |
Origin: | Lateral border of the scapula |
Insertion: | Greater tubercle of the humerus |
Action: | External rotation, weak adduction |
Innervation: | Axillary nerve (C5, C6) |
C Muscles of the rotator cuff: supraspinatus, infraspinatus, teres minor, and subscapularis
Right shoulder joint.
a Anterior view.
b Posterior view.
c Lateral view.
2.5 The Posterior Muscles of the Shoulder Joint: The Deltoid
A Schematic of the deltoid
Deltoid | |
Origin: | ① Clavicular part: lateral third of the clavicle ② Acromial part: acromion ③ Spinal part: scapular spine |
Insertion: | Deltoid tuberosity on the humerus |
Actions: | • Clavicular part: flexion (moves the arm and shoulder forward), internal rotation, adduction • Acromial part: abduction • Spinal part: extension (moves the arm and shoulder backward), external rotation, adduction Between 60° and 90° of abduction, the clavicular and spinal parts of the deltoid assist the acromial part of the muscle with abduction. |
Innervation: | Axillary nerve (C5, C6) |
