Anatomy of the Upper Limb: Musculature of the Arm and Forearm

In Lecturio ;) - A large number of different muscles makes the forearm and the hand one of the most complex structures in our musculoskeletal system and can cause issues for both medical professionals and students. The most common arm injuries occur in the upper arm, especially the radius.

Table of Contents

• Flexors of the Elbow
• Extensors of the Elbow
• Flexors of the Arm
• Extensors of the Arm
• Review Questions
• References

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Image : “Inflammation of a forearm extensor muscle” by scientificanimations.com. License: CC BY-SA 4.0

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Flexors of the Elbow

The flexors of the elbow include the brachialis muscle, the brachioradialis muscle, and the biceps brachii muscle.

Muscle	Origin	Insertion	Nerve supply	Function
Brachioradialis	Proximal two-thirds of lateral supracondylar ridge	Lateral surface of distal radius and pre-styloid process	Radial nerve (C6)	Weak flexor of the elbow, strong flexor when forearm mid-pronated
Brachialis	Anterior aspect of the humerus lateral to the deltoid tuberosity	Ulnar tuberosity	Musculocutaneous nerve (C5-C7)	Flexes the elbow and assists with supination.
Biceps brachii	Short head – coracoid process Long head – supraglenoid tubercle	Tuberosity of the radius	Musculocutaneous nerve (C5-C6)	Supinates the forearm and assists with elbow flexion
Extensor carpi radialis longus	Lateral supracondylar ridge	Dorsal aspect of 2nd metacarpal	Radial nerve (C6, C7)	Extend and abduct wrist
Extensor carpi radialis brevis	Lateral epicondyle (common extensor origin)	Dorsal aspect of the 3rd metacarpal	Deep branch of the radial nerve (C7)

Extensors of the Elbow

Triceps brachii

Long head – infraglenoid tubercle Lateral and medial heads – posterior humerus

Olecranon

Radial nerve (C6 – C8)

Extends the elbow

Flexors of the Arm

Divided into two groups – the common flexors and the deep flexors.

Common flexors

Muscle	Origin	Insertion	Nerve supply	Function
Pronator teres	Ulnar head: coronoid process of ulna Humeral head: medial epicondyle	Middle of lateral surface of radius	Median nerve (C7)	Pronates and flexes the forearm
Flexor carpi radialis	Medial epicondyle of humerus	Base of 2nd metacarpal		Flexes and abducts hand at wrist
Palmaris longus		Flexor retinaculum and palmar aponeurosis		Flexes hand at wrist and tenses palmar aponeurosis
Flexor carpi ulnaris	Olecranon and posterior ulna	Pisiform, hook of hamate, 5th metacarpal	Ulnar nerve (C8)	Flexes and adducts hand at wrist

Deep flexors

Muscle	Origin	Insertion	Nerve supply	Function
Flexor digitorum profundus	Proximal surfaces of medial and anterior surfaces of ulna and interosseous membrane	Medial four digits distal phalanges	Lateral muscle bellies to digits 2 and 3: Median nerve (C7, C8, T1) Medial muscle bellies to digits 4 and 5: Ulnar nerve (T1)	Flexes hand at wrist joint Flexes distal interphalangeal joint
Flexor pollicis longus	Anterior surface of radius and interosseous membrane	Distal phalanx of first digits	Anterior interosseous nerve (branch of median) (C8)	Flexes wrist Flexes interphalangeal and metacarpophalangeal joints of first digits
Pronator quadratus	Distal quarter of ulna	Distal quarter of radius		Pronates forearm

Extensors of the Arm

Also divided into two groups – the common extensors and the deep extensors.

Image: “Muscles That Move the Forearm” by Phil Schatz. License: CC BY 4.0

Common extensors

Muscle	Origin	Insertion	Nerve supply	Function
Extensor carpi radialis (longus and brevis)
Extensor digitorum	Lateral epicondyle (common extensor origin)	Extensor expansion of medial four digits	Posterior interosseous nerve (C7; from deep radal nerve)	Extend wrist Extend medial four digits at metacarpophalangeal and interphalangeal joints (fifth digit for EDM)
Extensor digiti minimi		Extensor expansion of fifth digit
Extensor carpi ulnaris	Lateral epicondyle and posterior surface of ulna	Dorsal aspect of fifth metacarpal		Extends and adducts wrist

Deep extensors

Muscles	Origin	Insertion	Nerve supply	Function
Supinator	Lateral epicondyle of humerus, supinator fossa and proximal ulna	Posterior, lateral and anterior surfaces of proximal radius	Deep branch of radial nerve (C8)	Supination of forearm
Abductor pollicis longus	Posterior surface of radius and ulna and interosseous membrane	Metacarpal of first digit	Posterior interosseous nerve (C7 and C8) from deep radial nerve	Extends wrist Abducts thumb and extends it at carpometacarpal joint
Extensor pollicis longus	Posterior surface of ulna and interosseous membrane	Dorsal surface of distal phalanx of first digit		Extends wrist Extends distal (EPL)/ proximal (EPB) phalanx of thumb at interphalangeal joint Extends metacarpophangeal and carpometacarpal joints
Extensor pollicis brevis	Posterior surface of radius and interosseous membrane	Dorsal surface of proximal phalanx of first digit
Extensor indicis	Posterior surface of the ulna	Extensor expansion of 2ndfinger	Posterior interosseous nerve (C7 and C8) from deep radial nerve	Extends 2nd finger and assists with hand extension

Review Questions

Solutions can be found below the references.

1. Which of the following muscles does not have any flexion capacity in the elbow or forearm?

1. Pronator teres muscle
2. Extensor carpi radialis longus muscle
3. Brachialis muscle
4. Brachioradialis muscle
5. Anconeus muscle

2. What nerve innervates the flexor carpi radialis muscle?

1. Axillary nerve
2. Radial nerve
3. Median nerve
4. Ulnar nerve
5. Musculocutaneous nerve

3. Which of the following muscles does not belong to the group of the dorsal ulnar and palmar-dorsal abductors?

1. Extensor carpi ulnaris muscle
2. Extensor digiti minimi muscle
3. Extensor digitorum muscle
4. Extensor indicis muscle
5. Flexor carpi ulnaris muscle