The axillary nerve or the circumflex nerve is a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

of the human body, that originates from the

brachial plexus The brachial plexus is a network of nerves (nerve plexus) formed by the anterior rami of the lower four Spinal nerve#Cervical nerves, cervical nerves and first Spinal nerve#Thoracic nerves, thoracic nerve (cervical spinal nerve 5, C5, Cervical spi ...

( upper trunk, posterior division, posterior cord) at the level of the

axilla The axilla (: axillae or axillas; also known as the armpit, underarm or oxter) is the area on the human body directly under the shoulder joint. It includes the axillary space, an anatomical space within the shoulder girdle between the arm a ...

(armpit) and carries nerve fibers from C5 and C6. The axillary nerve travels through the

quadrangular space The quadrangular space, also known as the quadrilateral space (of Velpeau) and the foramen humerotricipitale, is one of the three spaces in the axillary space. The other two spaces are: triangular space and triangular interval. Structure The ...

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 In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla (armpit) and the upper limb. Its origin is at the lateral margin of the first rib, before which it is c ...

, and in front of the

subscapularis The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the Glenohumeral joint, shoulder-joint. Structure The subscapularis is covere ...

, and passes downward to the lower border of that muscle. It then winds from anterior to posterior around the neck of the

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

, in company with the posterior humeral circumflex artery, through the

(bounded above by the teres minor, below by the teres major, medially by the long head of the

triceps brachii The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the back of the upper limb of many vertebrates. It consists of three parts: the medial, lateral, and long head. All three heads cross the elbow jo ...

, 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

branch. * The ''anterior branch'' (upper branch) winds around the

surgical neck of the humerus The surgical neck of the humerus is a bony constriction at the proximal end of shaft of humerus. It is situated distal to the greater tubercle and lesser tubercle, and proximal to the deltoid tuberosity. Clinical significance The surgical nec ...

, beneath the

deltoid muscle The deltoid muscle is the muscle forming the rounded contour of the shoulder, human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle is made up o ...

, 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 (or upper) 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

arises, on average, a distance of 6 mm (range 2–12 mm) from the terminal division of the posterior cord termination. * The trunk of the axillary nerve gives off an articular filament which enters the

shoulder joint The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial joint, synovial ball-and-socket joint and functionally as a diarthrosis and m ...

below the

Variation

Traditionally, the axillary nerve is thought to only supply the deltoid and teres minor. However, several studies on

cadaver A cadaver, often known as a corpse, is a Death, dead human body. Cadavers are used by medical students, physicians and other scientists to study anatomy, identify disease sites, determine causes of death, and provide tissue (biology), tissue to ...

s pointed out that the long head of

is innervated by a branch of the axillary nerve.

Function

The axillary nerve supplies two

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s in the arm: deltoid (a muscle of the shoulder) and teres minor (one of the

rotator cuff The rotator cuff (SITS muscles) is a group of muscles and their tendons that act to stabilize the human shoulder and allow for its extensive range of motion. Of the seven scapulohumeral muscles, four make up the rotator cuff. The four muscles a ...

muscles). The axillary nerve also carries sensory information from the

. 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

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

, 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. Direct trauma to the nerve can also lead to paralysis and loss of sensation.

Additional images

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

References

External links

* {{DEFAULTSORT:Axillary Nerve Nerves of the upper limb Axillas