The axillary nerve, or axillary nerve, is a signal pathway responsible for controlling certain shoulder muscles and carrying sensitive information from the lateral shoulder to the brain. Lesions that lead to functional limitations of the nerve can occur, for example, when the shoulder joint is dislocated or the humerus bone is fractured.
What is the axillary nerve?
The axillary nerve is a nerve in the shoulder area. It is part of the brachial plexus, a collection of different nerves above and below the collarbone. The brachial plexus does not form a homogeneous cord, but is characterized by a collection of similarly running nerves. Taken together, the individual fibers of the brachial plexus innervate the shoulder as well as the upper extremities and run adjacent to the posterior circumflex humeral artery, which is the artery that supplies blood to the deltoid muscle as well as the shoulder joint. The roots of the axillary nerve lie between the cervical segments C5 to C6 of the spinal cord, which together with the brain forms the central nervous system. Reflexes, such as those that represent a response to overstretching of muscles and tendons or pain, are often already wired through the spinal cord. Compared to intentional movements, they are therefore particularly fast and not subject to a person’s voluntary control.
Anatomy and structure
In the human body, the axillary nerve extends below the clavicle along the shoulder, passing through the lateral axillary gap (foramina axillaria). This represents the area at the axilla, which is terminated on one side by the upper arm bone (humerus) and on the other side by the head of the triceps (Musculus triceps brachii). This head is the caput longum, which is also the origin of the muscle on the scapula, while the caput mediale begins centrally on the humerus and the caput laterale originates laterally on the humerus. At the other end, the triceps attaches to the ulna (ulna). The axillary nerve is part of the brachial plexus, where it belongs to the infraclavicular branches of the nerve plexus, as it lies below the clavicle. Within the brachial plexus, the axillary nerve also belongs to the posterior fasciculus. Physiology also refers to the sensitive fibers of the axillary nerve as the cutaneus brachii lateralis superior nerve, since it extends into the shoulder subcutaneous tissue of the lateral part of the shoulder. It branches off from the other fibers even before the axillary gap.
Function and Tasks
The axillary nerve participates in the control of certain shoulder muscles. It usually innervates the deltoid muscle, which attaches to the upper arm and originates at the clavicle and scapula. The deltoid muscle plays an important role in lifting the arm. In addition, the axillary nerve provides nervous signals to the small round muscle (teres minor muscle), which is located on the back and originates from the margo lateralis scapulae on the scapula. The insertion of the teres minor muscle is located on the humerus. It participates in various arm movements. In some people, part of the axillary nerve leads as a variety not only to the deltoid and teres minor muscles, but also to the great round muscle (teres major muscle). Through its connection to these parts of the shoulder musculature, the axillary nerve also contributes to arm movements. The motor fibers of the nerve are responsible for this task. The control of reflexes originates in part from the spinal cord, whereas voluntary movements are planned and initiated in the brain. In addition to the motor fibers, the axillary nerve has sensitive portions that sense stimuli such as touch, pain, and temperature in the innervated areas of the body. Their action potentials follow the reverse path, traveling from the periphery to the central nervous system, where they partially trigger conscious sensations; however, part of the perceptual process occurs unconsciously. The sensitive fibers of the axillary nerve transmit perceptions such as touch, temperature, and pain. All fibers of the axillary nerve are the extended ends of nerve cells and transmit electrical impulses, which are action potentials that trigger the movements of muscles and mediate stimuli.
Diseases
Various diseases can damage the axillary nerve and thus impair its function.If the signal transmission of the nerve pathway is disturbed, motor function restrictions in the innervated shoulder muscles can be the result. In addition, sensory perception disorders in the lateral region of the shoulder and pain are possible. Possible causes of an axillary nerve lesion include shoulder dislocation, in which affected individuals dislocate or dislocate the shoulder joint. Often, the injury is already visible from the outside, as the dislocation leads to displacement of the shoulder joint. The clavicle usually has a deviated angle on the affected side. Doctors can often reset the dislocated joint after an injury without lasting consequential damage. However, as a complication, damage can occur to the axillary nerve or other surrounding tissues, so pain, loss of sensation and limited arm mobility are possible. Arthritis patients and others are at increased risk for shoulder dislocation and other joint deformities. However, functional limitations of the axillary nerve may also be due to lesions caused by a fracture of the humerus. In this context, the collum chirurgicum represents a typical weak point of the bone and fractures with above-average frequency. The fracture may directly damage the axillary nerve if a fragment injures the nerve, or indirectly as part of the healing process: to repair the bone, the bone forms new tissue and thickens at the affected site.
