The brachial plexus is a plexus of nerves that innervates the shoulders, arms, and chest wall as part of the peripheral nervous system with three main branches. The brachial plexus is composed of anterior spinal nerves from the lowest cervical vertebrae C5-C7 and the first thoracic vertebra Th1. A few nerve fibers originating from the 4th cervical vertebra (C4) and the 2nd thoracic vertebra (Th2) are also involved.
What is the brachial plexus?
The Latin term brachial plexus literally means “brachial plexus.” It is a plexus of nerves of the peripheral nervous system whose main function is to innervate muscles and skin parts of the chest, shoulders, arms and hands, both motor and sensory. The plexus is formed by spinal nerves originating anteriorly from the lowest cervical vertebrae (C5-C7) and the uppermost thoracic vertebra (Th1), supplemented by a few nerve fibers from C4 and Th2. The brachial plexus can be divided into the three divisions of trunci (trunks), fasciculi (bundles), and the individual principal nerves arising from them. Some of the spinal nerves emerging from the vertebrae branch when they enter one of the three trunci, so that it is not always possible to clearly delineate or assign certain spinal nerves to one of the three main trunci. Further branching occurs in the fasciculi, creating a kind of nervous network. The main nerves “responsible” for certain areas, or muscles, branch off from the nerve plexus, and their origin can be traced back to several spinal nerves in each case because of the interconnectedness within the brachial plexus.
Anatomy and structure
The brachial plexus is composed of the spinal nerves of the C5-Th1 spinal region exiting anteriorly between the vertebrae. In addition, the plexus also accommodates a few nerve fibers from C4 and Th2. The spinal nerves from C5 and C6 together form the main trunk truncus superior. The spinal nerve from the 7th cervical vertebra forms the main trunk truncus medius, and the junction of the lowest cervical nerve with the first thoracic nerve forms the truncus inferior. A portion of the main trunk nerves cross-links to form another three sub-trunks (fasciculi), the fasciculus lateralis, medialis and posterior. The partial bundling of the spinal nerves has the advantage for the motor and sensory nerves arising from the plexus that nerve fibers from several spinal nerves are usually involved. In the brachial plexus area, there are two cervical muscles, Musculus scalenus anterior and Musculus scalenus medius. Between the two muscles is a gap, the posterior scalenus gap, through which the brachial plexus nerves and the subclavian artery enter the axillary region.
Function and Tasks
The main task and function of the brachial plexus nerve plexus is motor and sensory innervation of the thoracic and shoulder muscles and the arm and hand muscles. The partial interconnection and union of the spinal nerves in the brachial plexus has the advantage that in the event of a lesion of a single spinal nerve, its function can be taken over to a certain extent by other nerve fibers. In addition, a kind of communication between the nerves is possible with a certain exchange of information about the instantaneous muscle parameters. The nerves that originate from the nerve plexus to supply “their” muscle are composed of mixed fibers. Efferent fibers carry the information for muscle contraction from the appropriate motor center to the muscle, or muscle part. Afferent, sensory (sensitive), fibers transmit sensory impressions to the appropriate centers in the brain, where they are processed and may be part of an automatic control circuit. Muscle spindles, which “measure” the tension of muscle fibers and, in combination with the Golgi tendon organs, transmit the proprioceptive state, serve as sensors. These can be very complex control circuits that enable automatic or semi-automatic movement. Nerve fibers that serve autonomic control – control that is not subject to will – are also an integral part of the nerves originating from the brachial plexus.
Diseases
The most common occurrence of discomfort or certain symptoms associated with the brachial plexus is a narrowing of the posterior scalenal nerve gap, which can lead to the development of a condition called scalenal syndrome.Symptoms of scalenus syndrome are pain in the forearm on the little finger side and paraesthesia that increases in the area when the forearm hangs down. When the posterior scalenus gap is narrowed, the oxygen supply to the tissue is usually also impaired because the supplying artery also runs through the scalenus gap. The scalenus syndrome is therefore often accompanied by a blue discoloration (cyanosis) of the tissue and by edema because of the lack of oxygen supply and because of the mechanical impairment of blood flow. In the case of a complete tear of the brachial plexus due to an accident, there is a total loss, complete paralysis of the muscles of the shoulder, chest, arms and hands. In case of a partial lesion of certain branches of the brachial plexus, symptomatic motor and sensory deficits of the affected muscle parts occur. Damage to the brachial plexus can also occur during the birth process if the birth canal is a little narrow for the baby. Traction forces can cause avulsion or avulsion injuries to the nerve plexus, resulting in obstetric plexus paresis. The paresis is usually manifested by paralysis of the affected arm. The damage often heals on its own; otherwise, surgical measures should be considered within the first 9 months. The brachial plexus may become inflamed in a type of autoimmune reaction, leading to neuralgic shoulder amyotrophy. The disease is manifested by severe pain in the shoulder and paralysis of the shoulder and upper arm muscles.
Typical and common nerve disorders
- Nerve pain
- Nerve inflammation
- Polyneuropathy
- Epilepsy
