Muscular branches of axillary nerve

At a glance

English

Muscular branches of axillary nerve

Latin (TA2)

Rami musculares nervi axillaris

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the muscular branches of axillary nerve

The axillary nerve is a terminal branch of the posterior cord of the brachial plexus, carrying fibres from the fifth and sixth cervical nerves. It passes backwards out of the axilla through the quadrangular space, below the shoulder joint, together with the posterior circumflex humeral artery. Just behind the surgical neck of the humerus it divides into an anterior and a posterior branch, and both give muscular branches.

The anterior branch winds forwards around the surgical neck on the deep surface of the deltoid, with the posterior circumflex humeral vessels, and reaches as far as the front of the muscle. Its branches supply the anterior and middle parts of the deltoid. The posterior branch gives a twig to teres minor, often with a small swelling on it, and branches to the posterior part of the deltoid, then turns round the back of the deltoid as the superior lateral cutaneous nerve of the arm.

These branches are what make the deltoid and teres minor work, so they control raising the arm sideways beyond the first few degrees and help rotate it laterally. Because the nerve lies so close to the bone, it is injured in dislocation of the shoulder, in fractures of the surgical neck, and by badly placed injections into the deltoid. The result is a flattened shoulder with weak abduction. Testing feeling over the lower outer deltoid, supplied by the cutaneous continuation, gives a quick check that the nerve is intact.

Course and supply

Arises from

Anterior and posterior branches of the axillary nerve (C5, C6), behind the surgical neck of the humerus.

Ends in

End in the anterior, middle and posterior parts of the deltoid and in teres minor.

Supplies

Motor to the deltoid, which abducts, flexes and extends the arm, and to teres minor, which rotates it laterally.