Axillary nerve
Encyclopedia
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.
s; 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).
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
.
, 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.
, compression of the axilla with a crutch or fracture of the surgical neck of the humerus. Injury to the nerve results in:
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
of the human body, that comes off the of the brachial plexus
Brachial plexus
The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...
(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
Quadrangular space
The quadrangular space is an axillary space in the arm. This is a clinically important anatomic space in the arm. In the quadrangular space, the axillary nerve and posterior circumflex humeral artery can be compressed or damaged in the space due to space occupying lesions or disruption in the...
with the posterior circumflex humeral artery and vein.
Muscular and sensory innervation
The axillary nerve supplies three muscleMuscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s; deltoid
Deltoid muscle
In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
(a muscle of the shoulder), teres minor (one of the rotator cuff
Rotator cuff
In anatomy, the rotator cuff is the group of muscles and their tendons that act to stabilize the shoulder. The four muscles of the rotator cuff, along with the teres major muscle, the coracobrachialis muscle and the deltoid, make up the seven scapulohumeral muscles of the human body.-Function:The...
muscles) and the long head of the triceps brachii (an elbow extensor).
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
Superior lateral cutaneous nerve of arm
The superior lateral cutaneous nerve of arm is the continuation of the posterior cord of the axillary nerve, after it pierces the deep fascia.-Course and targets:...
branch of the Axillary nerve).
When the axillary nerve splits off from the posterior cord, the continuation of the cord is the radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
.
Branches
It lies at first behind the axillary arteryAxillary 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 and the upper limb...
, 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 humerusSurgical neck of the humerusThe surgical neck of the humerus is a constriction below the tubercles of the greater tubercle and lesser tubercle.It is much more frequently fractured than the anatomical neck of the humerus. A fracture in this area is most likely to cause damage to the axillary nerve...
, beneath the deltoidDeltoidDeltoid can refer to:* The deltoid muscle, a muscle in the shoulder* Kite , also known as a deltoid, a type of quadrilateral* A deltoid curve, a three-sided hypocycloid* A leaf shape* The deltoid tuberosity, a part of the humerus...
, with the posterior humeral circumflex vessels. It continues as far as the anterior border of the deltoidDeltoidDeltoid can refer to:* The deltoid muscle, a muscle in the shoulder* Kite , also known as a deltoid, a type of quadrilateral* A deltoid curve, a three-sided hypocycloid* A leaf shape* The deltoid tuberosity, a part of the humerus...
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 deltoidDeltoidDeltoid can refer to:* The deltoid muscle, a muscle in the shoulder* Kite , also known as a deltoid, a type of quadrilateral* A deltoid curve, a three-sided hypocycloid* A leaf shape* The deltoid tuberosity, a part of the humerus...
. The posterior branch pierces the deep fascia and continues as the superior lateral cutaneous nerve of armSuperior lateral cutaneous nerve of armThe superior lateral cutaneous nerve of arm is the continuation of the posterior cord of the axillary nerve, after it pierces the deep fascia.-Course and targets:...
, 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.
- 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 jointDislocated shoulder
A dislocated shoulder occurs when the humerus separates from the scapula at the glenohumeral joint. The shoulder joint has the greatest range of motion of any joint in the body and as a result is particularly susceptible to dislocation and subluxation. Approximately half of major joint...
, compression of the axilla with a crutch or fracture of the surgical neck of the humerus. Injury to the nerve results in:
- Paralysis of the teres minor muscleTeres minor muscleThe teres minor is a narrow, elongated muscle of the rotator cuff.-Origin:It arises from the dorsal surface of the axillary border of the scapula for the upper two-thirds of its extent, and from two aponeurotic laminæ, one of which separates it from the infraspinatus muscle, the other from the...
and deltoid muscleDeltoid muscleIn human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
, 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. - Loss of sensation in the skin over a small part of the lateral upper armArmIn human anatomy, the arm is the part of the upper limb between the shoulder and the elbow joints. In other animals, the term arm can also be used for analogous structures, such as one of the paired forelimbs of a four-legged animal or the arms of cephalopods...
.