Learning Objectives
By the end of this lesson, the student should be able to:
- Identify the muscles of the upper arm and their compartmental organization.
- Describe the attachments, actions, and innervation of each muscle.
- Explain the functional roles of the anterior and posterior compartments.
- Apply anatomical knowledge to common clinical conditions such as biceps tendon rupture.
Overview of the Upper Arm
The upper arm is the region between the shoulder joint and the elbow joint. It contains four major muscles organized into two compartments:
Anterior Compartment (Flexor Compartment)
- Biceps brachii
- Brachialis
- Coracobrachialis
Posterior Compartment (Extensor Compartment)
- Triceps brachii
This section reviews their attachments, actions, and innervation.
Anterior Compartment
The anterior compartment contains three muscles, all innervated by the musculocutaneous nerve.
A useful mnemonic is BBC:
Biceps brachii
Brachialis
Coracobrachialis
Arterial supply: muscular branches of the brachial artery.
Biceps Brachii
The biceps brachii is a two-headed muscle that has no direct attachment to the humerus.
As its tendon enters the forearm, it gives rise to the bicipital aponeurosis, which forms the roof of the cubital fossa.
| Feature | Description |
|---|---|
| Attachments | Long head: supraglenoid tubercle of the scapula |
| Short head: coracoid process of scapula | |
| Insertion: radial tuberosity and forearm fascia via bicipital aponeurosis | |
| Actions | Supination of the forearm; flexion at the elbow and shoulder |
| Innervation | Musculocutaneous nerve (C6 reflex) |
Activity
Coracobrachialis
| Feature | Description |
|---|---|
| Attachments | Coracoid process → medial humeral shaft |
| Actions | Flexion and weak adduction of the arm |
| Innervation | Musculocutaneous nerve |
Brachialis
The brachialis lies deep to the biceps and forms the floor of the cubital fossa.
| Feature | Description |
|---|---|
| Attachments | Humeral shaft → ulnar tuberosity |
| Actions | Primary flexor of the elbow |
| Innervation | Musculocutaneous nerve (with radial nerve contribution) |
Clinical Relevance – Rupture of the Biceps Tendon
The long head of the biceps is one of the most commonly ruptured tendons. When ruptured, the muscle belly retracts, producing a visible bulge known as the “Popeye sign.”
Despite this, patients usually retain elbow flexion due to the brachialis and supinator muscles.
Posterior Compartment
The posterior compartment contains one muscle:
Triceps Brachii
This muscle has three heads, with the medial head lying deepest.
Arterial supply: profunda brachii artery
| Feature | Description |
|---|---|
| Attachments | Long head: infraglenoid tubercle |
| Lateral head: humerus (above radial groove) | |
| Medial head: humerus (below radial groove) | |
| Insertion: olecranon of the ulna. | |
| Actions | Extension at the elbow |
| Innervation | Radial nerve (C7 reflex) |
Note: In some individuals, the long head may receive innervation from the axillary nerve.
