The brachial plexus is a network of nerves that sends signals from the spine to the shoulder, arm, and hand. Damage to the brachial plexus can cause symptoms such as

• A limp or paralyzed arm
• Lack of muscle control in the arm, hand, or wrist
• Lack of feeling or sensation in the arm or hand

Brachial plexus injuries can happen because of shoulder trauma, tumors, or inflammation. Sometimes they happen during childbirth when a baby's shoulders become stuck during delivery and the nerves stretch or tear.

Some brachial plexus injuries may heal without treatment. Many children who are injured during birth improve or recover by 3 to 4 months of age. Treatment includes physical therapy and, in some cases, surgery.

The brachial plexus is a network of nerves that carries signals from the upper parts of the spinal cord to your shoulder, arm, and hand. These nerves involve movement and sensation and allow you to raise your arm and move your hand and wrists. Brachial plexus injuries (also known as Erb's palsy and Dejerine-Klumpke palsy) are caused by damage to those nerves, typically from trauma, tumors, inflammation, pressure, athletic injuries, or being stretched too far. Some brachial plexus injuries can happen to babies during birth.

Erb's palsy refers to numbness and paralysis of the upper brachial plexus. Dejerine-Klumpe palsy (also known as Klumpke's palsy) refers to loss of sensation in the wrist and hand and paralysis of the lower brachial plexus. A rare syndrome called Parsonage-Turner Syndrome, or brachial plexitis, causes inflammation of the brachial plexus without any obvious shoulder injury. 

Brachial Plexus is the nerve plexus associated with the lower cervical spinal nerves and first thoracic spinal nerve.

Spinal Nerves

The nerves connected to the spinal cord are the spinal nerves. The arrangement of these nerves is much more regular than that of the cranial nerves. All of the spinal nerves are combined sensory and motor axons that separate into two nerve roots. The sensory axons enter the spinal cord as the dorsal nerve root. The motor fibers, both somatic and autonomic, emerge as the ventral nerve root. The dorsal root ganglion for each nerve is an enlargement of the spinal nerve.

There are 31 spinal nerves, named for the level of the spinal cord at which each one emerges. There are eight pairs of cervical nerves designated C1 to C8, twelve thoracic nerves designated T1 to T12, five pairs of lumbar nerves designated L1 to L5, five pairs of sacral nerves designated S1 to S5, and one pair of coccygeal nerves. The nerves are numbered from the superior to inferior positions, and each emerges from the vertebral column through the intervertebral foramen at its level. The first nerve, C1, emerges between the first cervical vertebra and the occipital bone. The second nerve, C2, emerges between the first and second cervical vertebrae. The same occurs for C3 to C7, but C8 emerges between the seventh cervical vertebra and the first thoracic vertebra. For the thoracic and lumbar nerves, each one emerges between the vertebra that has the same designation and the next vertebra in the column. The sacral nerves emerge from the sacral foramina along the length of that unique vertebra.

Spinal nerves extend outward from the vertebral column to innervate the periphery. The nerves in the periphery are not straight continuations of the spinal nerves, but rather the reorganization of the axons in those nerves to follow different courses. Axons from different spinal nerves will come together into a systemic nerve. This occurs at four places along the length of the vertebral column, each identified as a nerve plexus, whereas the other spinal nerves directly correspond to nerves at their respective levels. In this instance, the word plexus is used to describe networks of nerve fibers with no associated cell bodies.

Of the four nerve plexuses, two are found at the cervical level, one at the lumbar level, and one at the sacral level (Figure 13.24). The cervical plexus is composed of axons from spinal nerves C1 through C5 and branches into nerves in the posterior neck and head, as well as the phrenic nerve, which connects to the diaphragm at the base of the thoracic cavity. The other plexus from the cervical level is the brachial plexus. Spinal nerves C4 through T1 reorganize through this plexus to give rise to the nerves of the arms, as the name brachial suggests. A large nerve from this plexus is the radial nerve from which the axillary nerve branches to go to the armpit region. The radial nerve continues through the arm and is paralleled by the ulnar nerve and the median nerve. The lumbar plexus arises from all the lumbar spinal nerves and gives rise to nerves enervating the pelvic region and the anterior leg. The femoral nerve is one of the major nerves from this plexus, which gives rise to the saphenous nerve as a branch that extends through the anterior lower leg. The sacral plexus comes from the lower lumbar nerves L4 and L5 and the sacral nerves S1 to S4. The most significant systemic nerve to come from this plexus is the sciatic nerve, which is a combination of the tibial nerve and the fibular nerve. The sciatic nerve extends across the hip joint and is most commonly associated with the condition sciatica, which is the result of compression or irritation of the nerve or any of the spinal nerves giving rise to it.

These plexuses are described as arising from spinal nerves and giving rise to certain systemic nerves, but they contain fibers that serve sensory functions or fibers that serve motor functions. This means that some fibers extend from cutaneous or other peripheral sensory surfaces and send action potentials into the CNS. Those are axons of sensory neurons in the dorsal root ganglia that enter the spinal cord through the dorsal nerve root. Other fibers are the axons of motor neurons of the anterior horn of the spinal cord, which emerge in the ventral nerve root and send action potentials to cause skeletal muscles to contract in their target regions. For example, the radial nerve contains fibers of cutaneous sensation in the arm, as well as motor fibers that move muscles in the arm.

Spinal nerves of the thoracic region, T2 through T11, are not part of the plexuses but rather emerge and give rise to the intercostal nerves found between the ribs, which articulate with the vertebrae surrounding the spinal nerve.

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Figure 13.24 Nerve Plexuses of the Body There are four main nerve plexuses in the human body. The cervical plexus supplies nerves to the posterior head and neck, as well as to the diaphragm. The brachial plexus supplies nerves to the arm. The lumbar plexus supplies nerves to the anterior leg. The sacral plexus supplies nerves to the posterior leg.

Symptoms of a brachial plexus injury may include:

• A limp or paralyzed arm
• Lack of muscle control in the arm, hand, or wrist
• A lack of feeling or sensation in the arm or hand
• Sudden pain in the shoulder or arm that may be stinging or burning

Although injuries can occur at any time, many brachial plexus injuries happen when a baby's shoulders become impacted during delivery and the brachial plexus nerves stretch or tear.  

Types of brachial plexus injuries are: 

• Neuropraxia or stretch, the mildest form in which the nerve has been damaged but not torn and causes some problems with nerve signaling 
• Neuroma, in which the nerve has torn and healed but scar tissue puts pressure on the injured nerve and prevents it from conducting signals to the muscles 
• Rupture, in which the nerve is torn but not at the spinal attachment
• Avulsion, the most severe type, in which the nerve is cut or torn from the spinal cord. There is also an incomplete form of avulsion in which part of the nerve is damaged and which leaves some opportunity for the nerve to slowly recover function

The severity of a brachial plexus injury depends on the nerves affected and the extent of the injury. Some injuries may be temporary, while others are chronic. Some brachial plexus injuries may heal without treatment. Some children who are injured during birth improve or recover on their own by 3 to 4 months of age. Most children recover some function through physical and occupational therapy.

In some cases (such as avulsion and rupture injuries), surgery is needed. Medications can help with pain management and assistive devices, such as splints or braces, may be needed by some individuals.