Axillary Nerve:The axillary nerve is a major peripheral nerve of the human body, that arises from the brachial plexus (upper trunk, posterior division, posterior cord) at the level of the axilla.
Spinal roots: C5 and C6.
Course of the Axillary Nerve
- Immediately after its creation, the axillary nerve occupies posteriorly to the axillary artery and anteriorly to the muscle of the subscapularis, next exits the axilla posteriorly via the quadrangular space. It is conducted by the posterior circumflex humeral artery.
- In the posterior region of the scapula, the axillary nerve terminates by division into two branches-
A. Posterior terminal branch – Motor supply to the teres minor muscle, and innervates the sensory supply to the inferior part of the deltoid.
B.Anterior terminal branch – Motor supply to the deltoid muscle
The axillary nerve additionally contributes articular branches to the shoulder joint itself.
The Quadrangular Space
The quadrangular space is a hollow in the muscles of the posterior scapular region. It is a pathway for neurovascular structures to pass from the axilla to the posterior shoulder and arm. Its boundaries are:
• Superior – Subscapularis and Teres minor muscle.
• Inferior – Teres major muscle.
• Medially – Long head of triceps brachii muscle.
• Laterally – Surgical neck of humerus
The axillary nerve and posterior circumflex humeral artery cross within the quadrangular space.
Motor functions of the Axillary Nerve
Sensory functions of the Axillary Nerve
Gives rise to the superior lateral cutaneous nerve of the arm, that innervates the skin covering the lower deltoid.
Injury to the Axillary Nerve
Stress or damage to the axillary nerve, which serves the deltoid muscles and skin of the shoulder. Paralysis of the deltoid and teres minor muscles. This renders unable to abduct the arm of the affected limb.