The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus (upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein to innervate the deltoid and teres minor.
Structure
The nerve lies at first behind the axillary artery, and in front of the subscapularis, beneath the deltoid muscle, with the posterior humeral circumflex vessels. It continues as far as the anterior border of the deltoid to provide motor innervation. The anterior branch also gives off a few small cutaneous branches, which pierce the muscle and supply in the overlaying skin.
- The posterior branch (lower branch) supplies the teres minor and the posterior part of the deltoid.
Function
The axillary nerve supplies two muscles in the arm: deltoid (a muscle of the shoulder) and teres minor (one of the rotator cuff muscles).
The axillary nerve also carries sensory information from the shoulder joint. It also innervates the skin, covering the inferior region of the deltoid muscle, known as the regimental badge area. This is innervated by the superior lateral cutaneous nerve branch of the axillary nerve.
The posterior cord of the brachial plexus splits inferiorly to the glenohumeral joint giving rise to the axillary nerve which wraps around the surgical neck of the humerus, and the radial nerve which wraps around the humerus anteriorly and descends along its lateral border.
Clinical significance
The axillary nerve may be injured in anterior-inferior dislocations of the shoulder joint, compression of the axilla with a crutch or fracture of the surgical neck of the humerus. An example of injury to the axillary nerve includes axillary nerve palsy. Injury to the nerve results in:
- Paralysis of the teres minor muscle and deltoid muscle, resulting in loss of abduction of arm (from 15-90 degrees), weak flexion, extension, and rotation of shoulder. Paralysis of deltoid and teres minor muscles results in flat shoulder deformity.
- Loss of sensation in the skin over the regimental badge area.
Additional images
<gallery>
File:Brachial_plexus_color.svg|Brachial plexus with courses of spinal nerves shown
File:Gray810.png|Suprascapular and axillary nerves of right side, seen from behind.
File:Gray811and813.PNG|Cutaneous nerves of right upper extremity.
File:Gray812and814.svg|Diagram of segmental distribution of the cutaneous nerves of the right upper extremity.
File:Slide6a.JPG|Axillary nerve
File:Slide2dj.JPG|Axillary nerve
File:Slide12dj.JPG|Axillary nerve
File:Slide18OOO.JPG|Axillary nerve
</gallery>
See also
- Axillary nerve dysfunction