[4.2] UL 2: Arm and Forearm Muscles

Biceps Brachii, Coracobrachialis, Brachialis

What muscles, mainly flexors, compose the anterior compartment of the arm?

Triceps Brachii

What muscles, mainly extensors, compose the anterior compartment of the arm?

Biceps brachii, Long head

What is the muscle shown in the photo, and what head?

Biceps brachii, Short head

What is the muscle shown in the photo, and what head?

Long head - lateral, Short head - medial

Which heads of the biceps brachii are located laterally and medially?

Glenohumeral joint capsule → bicipital groove — Long head

What is the course of the long head tendon that makes it appear shorter?

Coracoid process — Short head

Where does the short head of the biceps brachii arise?

Radial tuberosity — Biceps brachii

Where does the biceps brachii insert?

Primary arm supination — Biceps brachii

What is the biceps brachii's primary action on the forearm?

Strong elbow flexor when the arm is fully supinated — Biceps brachii

When is the biceps brachii a particularly strong flexor of the elbow?

Weak shoulder flexor — Biceps brachii

What is the biceps brachii's action at the shoulder joint?

Pectoralis major and deltoid — Upper biceps tendons

Which muscles cover the upper tendons of the biceps brachii?

Coracobrachialis

What is the muscle shown in the photo?

Deep to the biceps brachii — Coracobrachialis

Where is the coracobrachialis located relative to the biceps brachii?

Coracoid process — Coracobrachialis origin

What is the origin of the coracobrachialis?

Medial aspect of the humeral shaft — Coracobrachialis insertion

Where does the coracobrachialis insert?

Shoulder flexion and arm adduction — Coracobrachialis actions

What are the actions of the coracobrachialis?

Brachialis

What is the muscle shown in the photo?

Distal anterior surface of the humerus — Brachialis origin

Where does the brachialis originate?

Coronoid process of the ulna — Brachialis insertion

Where does the brachialis insert?

Primary elbow flexion regardless of pronation or supination — Brachialis action

What is the action of the brachialis?

Triceps brachii, Long head

What is the muscle shown in the photo, and what head?

Triceps brachii, Lateral head

What is the muscle shown in the photo, and what head?

Triceps brachii, Medial head

What is the muscle shown in the photo, and what head?

Primary elbow extensor — Triceps brachii

What is the primary muscle responsible for elbow extension?

Long, Lateral, Medial heads

What are the three heads of the triceps brachii?

Olecranon process of ulna — Triceps brachii insertion

Where does the triceps brachii insert?

Primary extensor of the elbow joint — Triceps brachii

What is the primary action of the triceps brachii?

Armpit — Axilla

What is another name for the axilla?

Pyramid-shaped space between the upper arm and side of the chest — Axilla

How is the axilla described anatomically?

Pectoralis major, pectoralis minor, and subclavius — Anterior border

What muscles form the anterior border of the axilla?

Latissimus dorsi, subscapularis, and teres major — Posterior border

What muscles form the posterior border of the axilla?

Serratus anterior and upper four or five ribs — Medial border

What structures form the medial border of the axilla?

Biceps brachii and coracobrachialis — Lateral border

What muscles form the lateral border of the axilla?

Mostly flexors — Anterior compartment of the forearm

What is the predominant function/type of muscles in the anterior forearm compartment?

Four muscles — Layer 1

How many muscles are in Layer 1 of the anterior forearm?

Pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris — Layer 1

What muscles make up Layer 1 of the anterior forearm?

Medial epicondyle via a common tendon — Pronator teres, FCR, palmaris longus, and FCU

What is the common tendon origin shared by the superficial anterior forearm muscles?

Flexor digitorum superficialis — Layer 2

Which muscle forms Layer 2 of the anterior forearm?

Flexor digitorum profundus and flexor pollicis longus — Layer 3

Which muscles form Layer 3 of the anterior forearm?

Pronator quadratus — Layer 4

Which muscle forms Layer 4 of the anterior forearm?

Anterior Palmar Ligament

What is the structure shown in the photo?

Covers the tendons in the wrist area — Anterior palmar ligament

What does the anterior palmar ligament cover?

Prevents bow-stringing of the tendons during flexion — Anterior palmar ligament

What is the function of the anterior palmar ligament?

Flexor Retinaculum

What is the structure shown in the photo?

Forms the root of the concavity formed by the carpal bones — Flexor retinaculum

What role does the flexor retinaculum play in the carpal region?

Passage for 10 structures of the anterior fascial compartment — Flexor retinaculum

What passes through the flexor retinaculum according to the notes?

Palmaris longus — Does NOT pass under the flexor retinaculum

Which anterior forearm muscle lies superficially to the flexor retinaculum rather than passing underneath it?

Extensor Retinaculum

What is the structure shown in the photo?

Holds the tendons of the posterior fascial compartment — Extensor retinaculum

What is the function of the extensor retinaculum?

Pronator Teres

What is the muscle shown in the photo?

Humeral head and ulnar head — Pronator teres

What are the two heads of the pronator teres?

Medial supracondylar ridge of the humerus — Origin of humeral head

Where does the humeral head of the pronator teres originate?

Coronoid process of the ulna — Origin of ulnar head

Where does the ulnar head of the pronator teres originate?

Lateral surface of the radius — Pronator teres insertion

Where does the pronator teres insert?

Forearm pronation — Main action of pronator teres

What is the main action of the pronator teres?

Elbow flexion — Assistive action of pronator teres

What secondary action does the pronator teres assist with?

Foramen underneath the muscle — Passage of neurovascular structures

What is located underneath the pronator teres, and what passes through it?

Flexor Carpi Radialis

What is the muscle shown in the photo?

Medial epicondyle of the humerus — FCR origin

Where does the flexor carpi radialis originate?

Base of the 2nd and 3rd metacarpals — FCR insertion

Where does the flexor carpi radialis insert?

Wrist flexion and abduction — FCR actions

What are the actions of the flexor carpi radialis?

Palmaris Longus

What is the muscle shown in the photo?

Does not pass under the flexor retinaculum — Palmaris longus

What is distinctive about the palmaris longus in relation to the flexor retinaculum?

Between flexor carpi radialis and flexor carpi ulnaris — Palmaris longus location

Where is the palmaris longus located in relation to the flexor carpi radialis and flexor carpi ulnaris?

10% — Approximate population in which palmaris longus is absent

In approximately what percentage of people is the palmaris longus absent?

Medial epicondyle of the humerus — Palmaris longus origin

Where does the palmaris longus originate?

Flexor retinaculum and palmar aponeurosis — Palmaris longus insertion

Where does the palmaris longus insert?

Wrist flexion and tension of the palmar aponeurosis — Palmaris longus actions

What are the actions of the palmaris longus?

Flexor Carpi Ulnaris

What is the muscle shown in the photo?

Groove at the origin associated with the ulnar nerve — Cubital tunnel

What is the cubital tunnel and which nerve is associated with it?

Medial epicondyle of the humerus — Humeral head of FCU origin

Where does the humeral head of the flexor carpi ulnaris originate?

Medial aspect of olecranon process and posterior border of ulna — Ulnar head of FCU origin

Where does the ulnar head of the flexor carpi ulnaris originate?

Wrist flexion and adduction — Flexor carpi ulnaris action

What is the action of the flexor carpi ulnaris listed in your notes?

Flexor Digitorum Superficialis

What is the muscle shown in the photo?

Base of middle phalanges of medial four fingers (no thumb)

Where does flexor digitorum superficialis insert?

Medial epicondyle of humerus + medial border of coronoid process of ulna

What is the origin of the humeral head of flexor digitorum superficialis?

Oblique line on anterior surface of radial shaft

What is the origin of the radial head of flexor digitorum superficialis?

Flexor digitorum superficialis (FDS)

Which muscle forms four tendons that pass under the flexor retinaculum and attach to the bases of the middle phalanges?

Tendinous arch of FDS

What structure contains openings through which the flexor digitorum profundus tendons pass?

Flexion of the middle phalanx

What is the main action of flexor digitorum superficialis?

Flexion of proximal phalanx and hand

What are the assisting actions of flexor digitorum superficialis?

Flexor Digitorum Profundus

What is the muscle shown in the photo?

Flexor digitorum profundus (FDP)

Which deep anterior forearm muscle sends four tendons through the splits of flexor digitorum superficialis?

Anteromedial surface of ulnar shaft

What is the origin of flexor digitorum profundus?

Base of distal phalanges of medial four fingers

Where does flexor digitorum profundus insert?

Flexion of the distal phalanx

What is the main action of flexor digitorum profundus?

Flexion of middle and proximal phalanges and wrist

What are the assisting actions of flexor digitorum profundus?

Flexor Pollicis Longus

What is the muscle shown in the photo?

Flexor pollicis longus (FPL)

Which is the only long flexor of the thumb?

Pollex — thumb

What is the medical term for the thumb?

Anterior surface of radial shaft

What is the origin of flexor pollicis longus?

Base of distal phalanx of thumb

Where does flexor pollicis longus insert?

Flexion of distal phalanx of thumb

What is the action of flexor pollicis longus?

Pronator Quadratus

What is the muscle shown in the photo?

Pronator quadratus

Which short, flat, rectangular, wristband-like muscle connects the radius and ulna?

Anterior surface of ulnar shaft

What is the origin of pronator quadratus?

Anterior surface of radial shaft

Where does pronator quadratus insert?

Pronation at the radioulnar joint

What is the main action of pronator quadratus?

Stabilization of the radioulnar connection

What is the additional action of pronator quadratus?