Anterior compartment of arm

Question 1

Coracobrachialis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 1

• Origin - apex of the coracoid process, where it is fused with the medial side of the short head of biceps.
• Insertion - Midway along the medial border of the humerus.
• Nerve supply - Musculocutaneous nerve (C5, 6).
• Action - Weak flexor and adductor of shoulder joint.

Question 2

Biceps:
* Origin
* Insertion
* Nerve supply
* Action

Answer 2

• Origin - long head - arises from the supraglenoid tubercle and adjoining part of the glenoid labrum of the scapula. Short head - arises from the apex of the coracoid process with and to the lateral side of coracobrachialis.
• Insertion - radial tuberosity.
  The tendinous origin of each head expands into a fleshy belly.
  The 2 bellies lie side by side, loosely connected by areolar tissue but do not merge until just above the elbow joint, below the convexity of the muscle bellies. The flattened tendon at the lower end rotates (anterior surface laterally) as it passes through the cubital fossa to its insertion into the posterior border of the tuberosity of the radius.
  A bursa separates the tendon from the anterior part of the tuberosity.
  At the level of the elbow joint, the tendon has a broad medial expansion, the bicipital aponeurosis which is inserted by way of the deep fascia of the forearm into the subcutaneous border of the upper end of the ulna.
• Nerve supply - Musculocutaneous nerve (C5, 6) with one branch to each belly.
• Action - powerful flexor of elbow. Weak flexor of the shoulder.

Question 3

Brachialis:
* Origin
* Insertion
* Nerve supply
* Action

Answer 3

• Origin - Arises from the front of the lower half of the humerus and the medial intermuscular septum. Its upper fibres clasp the deltoid insertion and some fibres arise from the lower part of the radial groove.
• Insertion - coronoid process and the tuberosity of the ulna.
• Nerve supply - Musculocutaneous nerve (C5, 6). A small lateral part of the muscle is innervated by a branch of the radial nerve (C7).
• Action - flexor of elbow joint.