Muscles - Upper Arm

Question 1

What are the muscles of the anterior compartment?

Answer 1

These are the biceps brachii, the coracobrachialis and the brachialis.

Question 2

Biceps brachii

Answer 2

It is a two-headed muscle, but the majority of the muscle is located anteriorly to the humerus - it has no attachment to the bone itself.

As the biceps enters the forearm, a sheet of connective tissue is given off - the bicipital apeuneurosis. This forms the roof of the cubital fossa and blends with the deep fascia of the anterior forearm.

Origin (long head) - supraglenoid tubercle of the scapula

Origin (short head) - coracoid process of the scapula

Insertion - distally to radial tuberosity and the fascia of the forearm, via the bicipital aponeurosis.

Innervation - musculocutaenous nerve - bicep tendon reflex test spinal segment C6.

Function - supination of forearm and flexion at the elbow and shoulder.

Question 3

Coracobrachialis

Answer 3

Lies deep to the biceps brachii.

Origin - coracoid process. It then passes through the axilla.

Insertion - humerus, at the level of the deltoid tuberosity.

Innervation - musculocutaenous nerve

Function - Flexion of the arm and shoulder. Weak adduction

Question 4

Brachialis

Answer 4

More distal 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.

Function - Flexion of the elbow

Innervation - musculocutaenous nerve

Question 5

Clinical relevance: rupture of the biceps tendon

Answer 5

A complete rupture of any tendon in the body is rare. However, the biceps brachii tendon is the more common tendon ruptures.

It produces a characteristic sign on flexing the elbow - a bulge where the muscle belly is, called the ‘Popeye sign’

Patient would not notice much change in weakness due to the action of the brachialis and the supinator muscles.

Question 6

What are the muscles of the posterior compartment?

What is the blood supply to these muscles?

Answer 6

This is just the triceps brachii.

Profunda brachii artery

Question 7

Triceps brachii

When tapping on the triceps tendon, what is being tested?

Answer 7

Origin (long head) - infraglenoid tubercle

Origin (medial head) - humerus, inferior to the radial groove

Origin (lateral head) - humerus, superior to the radial groove

Insertion - heads converge into a tendon, which inserts into the olecranon of the ulna.

Function - extension of the arm at the elbow.

Innervation - radial nerve

Note: a tap on the triceps tendon tests C7. In some individuals, the long head is innervated by the axillary nerve.