Muscles of the arm (brachium)

What are the compartments of the arm (brachium) and which nerves innervate each?

Anterior compartment (flexors); primarily innervated by musculocutaneous nerve

- biceps brachii

- brachialis

- coracobrachialis

Posterior compartment (extensors); innervated by radial nerve

- triceps brachii

- anconeus

What are the compartments of the arm partitioned by?

The lateral and medial intermuscular septum

which is stronger - flexors or extensors of the arm?

flexors

• almost 2x strong as extensors

Biceps brachii: action and innervation

A: shoulder flexion

• fixed origin: shoulder flexion, forearm supination

• short head: assist shoulder adduction

• long head: may assist shoulder abduction when humerus is in ER

• fixed insertion: elbow flexion

N: musculocutaneus nerve; C5, C6

biceps brachii origin + insertion

O:

• long head - supraglenoid tubercle of scapula

• short head - apex of coracoid process of scapula

I:

• radial tubersosity on radius and bicipital aponeurosis

brachialis origin + insertion

O:

• distal ½ of anterior surface of humerus and both medial and lateral IM septa

I:

• tuberosity and coronoid process of ulna

Brachialis: action and innervation

A: elbow flexion

N: musculocutaneus nerve and radial nerve; C5, C6

coracobrachialis origin + insertion

O:

• apex of coracoid process of scapula

I:

• medial surface of middle of shaft of humerus (opposite of deltoid tuberosity)

Coracobrachialis: action and innervation

A: shoulder flexion and ADD

N: musculocutaneus nerve; C6, C7

triceps brachii origin + insertion

O:

• long head: infraglenoid tubercle of scapula

• lateral head: lateral and posterior surfaces of proximal ½ of bofy of humerus ABOVE RADIAL GROOVE and lateral IM septum

• medial head: distal 2/3 of medial and posterior surfaces of humerus BELOW RADIAL GROOVE and medial IM septum

I:

• posterior surface of olecranon process of ulna and antebrachial fascia

triceps brachii: action and innervation

A: elbow EXT; long head assists w/ shoulder EXT

• long head assists w/shoulder extension + adduction

N: radial nerve; C6, C7, C8, T1

anconeus origin + insertion

O:

• posterior surface on lateral epicondyle of humerus

I:

• lateral side of olecranon process and upper ¼ of posterior surface of body of ulna

anconeus: action and innervation

A: elbow EXT

• may stabilize ulan during pronation and supination

N: radial nerve; C7, C8

what are the spaces of the posterior shoulder region?

-quadrangular space

-triangular space

-triceps hiatus

*see slide 11 for picture

what are the boundaries of the quadrangular space? What runs through it?

Boundaries:

- superior border: teres minor

- inferior border: teres major

- lateral border: humerus

- medial border: long head triceps brachii

Contents:

- axillary nerve

- posterior circumflex humeral artery and vena comitantes

what are the boundaries of the triangular space? What runs through it?

Boundaries:

- superior border: teres minor

- lateral border: triceps brachii long head

- inferior border: teres major

Contents:

- circumflex scapular artery

what are the boundaries of the triceps hiatus space? What runs through it?

Boundaries:

-superior border: teres major

-lateral border: lateral head* of triceps brachii

-medial border: triceps brachii long head

Contents:

-radial nerve

-profunda brachii artery