The axillary nerve or the circumflex nerve is a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

of the human body, that originates from the

brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

(

upper trunk The upper (superior) trunk is part of the brachial plexus. It is formed by joining of the ventral rami of the fifth (C5) and sixth (C6) cervical nerves. The upper trunk divides into an anterior and posterior division. The branches of the upper tru ...

posterior division The dorsal ramus of spinal nerve (or posterior ramus of spinal nerve, or posterior primary division) is the posterior division of a spinal nerve. The dorsal ramus (Latin for branch, plural ''rami'' ) is the dorsal branch of a spinal nerve that fo ...

posterior cord The posterior cord is a part of the brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the ...

) at the level of the

axilla The axilla (also, 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 and the thoracic cage, bounded superior ...

(armpit) and carries

nerve fibers A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

from C5 and C6. The axillary nerve travels through the

quadrangular space The quadrangular space, also known as the quadrilateral space f 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 q ...

with the

posterior circumflex humeral artery The posterior humeral circumflex artery (posterior circumflex artery, posterior circumflex humeral artery) arises from the third part of axillary artery at the lower border of the subscapularis, and runs posteriorly with the axillary nerve through ...

and vein to innervate the deltoid and

teres minor The teres minor (Latin ''teres'' meaning 'rounded') is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the ...

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 ...

, 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 shoulder-joint. Structure It arises from its medial two-thirds and Som ...

, 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 (; ) 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 and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

, in company with the

posterior humeral circumflex artery The posterior humeral circumflex artery (posterior circumflex artery, posterior circumflex humeral artery) arises from the third part of axillary artery at the lower border of the subscapularis, and runs posteriorly with the axillary nerve throug ...

, through the

(bounded above by the

, below by the

teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meaning ...

, 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 Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with ba ...

, and laterally by the

surgical neck 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 n ...

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 human shoulder. It is also known as the 'common shoulder muscle', particularly in other animals such as the domestic cat. Anatomically, the deltoid muscle appears to be 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

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 ball-and-socket joint and functionally as a diarthrosis and multiaxial joint. ...

below the

Variation

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

cadaver A cadaver or corpse is a dead human body that is used by medical students, physicians and other scientists to study anatomy, identify disease sites, determine causes of death, and provide tissue to repair a defect in a living human being. Stud ...

s pointed out that the long head of

is innervated by a branch of the axillary nerve.

Function

The axillary nerve supplies two

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

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

(one of the

rotator cuff The rotator cuff 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 are the supraspi ...

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

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 The teres minor (Latin ''teres'' meaning 'rounded') is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the ...

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