Overview
There are three muscles located in the anterior compartment of the upper arm – biceps brachii, coracobrachialis and brachialis.
Muscles
Biceps Brachii
The biceps brachii is a two-headed muscle and is the only muscle of the anterior compartment of the arm to cross two joints (shoulder and elbow)
- Origins:
- Long head – supraglenoid tubercle of the scapula
- Short head – coracoid process of the scapula.
- Course:
- The long head remains tendinous as it passes through the shoulder joint and through the intertubercular groove of the humerus
- As the tendon of biceps brachii enters the forearm, a connective tissue sheet is given off – the bicipital aponeurosis, forming the roof of the cubital fossa and blending with the deep fascia of the anterior forearm.
- Insertion: Both heads insert into the radial tuberosity and the fascia of the forearm via the bicipital aponeurosis.
- Action: Supination of the forearm and flexes the arm at the elbow and at the shoulder.
- Innervation: Musculocutaneous nerve. The bicep tendon reflex tests spinal cord segment C6.
Coracobrachialis
The coracobrachialis muscle lies deep to the biceps brachii in the arm.
- Origin: Originates from the coracoid process of the scapula.
- Insertion: The muscle passes through the axilla, and attaches the medial side of the humeral shaft, at the level of the deltoid tubercle.
- Action: Flexion of the arm at the shoulder, and weak adduction.
- Innervation: Musculocutaneous nerve.
Brachialis
The brachialis muscle lies deep to the biceps brachii, and is found more distally than the other muscles of the arm. It forms the floor of the cubital fossa.
- Origin: Medial and lateral surfaces of the humeral shaft
- Insertion: Ulnar tuberosity, just distal to the elbow joint.
- Action: Flexion at the elbow.
- Innervation: Musculocutaneous nerve, with contributions from the radial nerve.
Innervation
All muscles of the anterior compartment are innervated by the musculocutaneous nerve.
Arterial Supply
Arterial supply to the anterior compartment of the upper arm is via muscular branches of the brachial artery.