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.
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Inflammation forearm extensor muscle

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

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 the 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 the lateral surface of radius Median nerve (C7) Pronates and flexes the forearm
Flexor carpi radialis Medial epicondyle of humerus Base of the 2nd metacarpal Flexes and abducts hand at the wrist
Palmaris longus Flexor retinaculum and palmar aponeurosis Flexes hand at the 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 the wrist

Deep flexors

Muscle Origin Insertion Nerve supply Function
Flexor digitorum profundus Proximal surfaces of medial and anterior surfaces of the 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 the ulna Distal quarter of the radius Pronates forearm

Extensors of the Arm

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

Muscles That Move the Forearm

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 the deep radial nerve) Extend wrist
Extend medial four digits at metacarpophalangeal and interphalangeal joints (fifth digit for EDM)
Extensor digiti minimi Extensor expansion of the fifth digit
Extensor carpi ulnaris Lateral epicondyle and posterior surface of ulna Dorsal aspect of the 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 the 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 the first digit Extends wrist
Extends distal (EPL)/ proximal (EPB) phalanx of thumb at interphalangeal joint
Extends metacarpophalangeal and carpometacarpal joints
Extensor pollicis brevis Posterior surface of radius and interosseous membrane Dorsal surface of proximal phalanx of the first digit
Extensor indicis Posterior surface of the ulna Extensor expansion of 2nd finger 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
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