Axillary nerve

Nerve: Axillary nerve
Brachial plexus. (Axillary nerve is visible in gray near center.)
The suprascapular, axillary, and radial nerves. (Axillary labeled at upper right.)
Latin	nervus axillaris
Gray's	subject #210 934
Innervates	deltoid, teres minor, triceps brachii (long head), axilla
From	posterior cord (C5, C6)

The axillary nerve or the circumflex nerve is a nerve of the human body, that comes off the of the brachial plexus (middle 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.

Muscular and sensory innervation

The axillary nerve supplies three muscles; deltoid (a muscle of the shoulder), teres minor (one of the rotator cuff muscles) and the long head of the triceps brachii (an elbow extensor).^[1]

The axillary nerve also carries sensory information from the shoulder joint, as well as the skin covering the inferior region of the deltoid muscle - the "regimental badge" area (which is innervated by the Superior Lateral Cutaneous Nerve branch of the Axillary nerve).

When the axillary nerve splits off from the posterior cord, the continuation of the cord is the radial nerve.

Branches

It lies at first behind the axillary artery, and in front of the subscapularis, and passes downward to the lower border of that muscle.

It then winds backward, in company with the posterior humeral circumflex artery, through a quadrilateral space bounded above by the teres minor, below by the teres major, medially by the long head of the triceps brachii, and laterally by the surgical neck of the humerus, and divides into an anterior, a posterior, and a collateral branch to the long head of the triceps brachii branch.

• The anterior branch (upper branch) winds around the surgical neck of the humerus, beneath the deltoid, 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. The posterior branch pierces the deep fascia and continues as the superior lateral cutaneous nerve of arm, which sweeps around the posterior border of the deltoid and supplies the skin over the lower two-thirds of the posterior part of this muscle, as well as that covering the long head of the triceps brachii.

• The motor branch of the long head of the triceps brachii arises, on average, a distance of 6 mm (range 2–12 mm) from the terminal division of the posterior cord termination.^[1]

• The trunk of the axillary nerve gives off an articular filament which enters the shoulder-joint below the subscapularis.

Injury

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. Injury to the nerve results in:

1. 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 & teres minor results in Flat shoulder deformity.
2. Loss of sensation in the skin over a small part of the lateral upper arm.

References

1. ^ ^{a b} de Se`ze MP, Rezzouk J, de Se`ze M, Uzel M, Lavignolle B, Midy D, Durandeau A (2004). "Does the motor branch of the long head of the triceps brachii arise from the radial nerve?". Surg Radiol Anat 26 (6): 459–461. doi:10.1007/s00276-004-0253-z. PMID 15365769. 

Additional images

• 

  Brachial plexus

• 

  Brachial plexus with courses of spinal nerves shown

• 

  Suprascapular and axillary nerves of right side, seen from behind.

• 

  Cutaneous nerves of right upper extremity.

• 

  Diagram of segmental distribution of the cutaneous nerves of the right upper extremity.

• 

  Back of right upper extremity, showing surface markings for bones and nerves.

Gray's Figure 1236: Back of right upper extremity, showing surface markings for bones and nerves with English titling. http://www.bartleby.com/107/illus1236.html

External links

• Duke Orthopedics axillary_nerve
• Axillary+nerve at eMedicine Dictionary

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.