A nerve plexus refers to a network of intersecting nerves that serve the same area of the body. Nerve plexuses form along the trunk of the body from nerve fibers of adjacent spinal nerves exiting the spinal column. The axons of spinal nerves join together to form the nerve plexus, and these fibers continue to branch and fuse as they travel toward their designated body part (4). Here, the term “plexus” describes the “web” of nerve fibers without their associated cell bodies (1). These anatomical structures are extremely useful for anesthesiologists and pain specialists, who often must block pain signals from a specific region of the body. 

Nerve plexuses exist in four different areas along the spinal column, with each plexus mediating the nerves that innervate a separate body area. The cervical plexus is located at the top of the spinal column and arises from the axons of spinal nerves C1 through C3 (1). Nerves from the cervical plexus connect to the head, neck, and shoulder (4). The brachial plexus comprises fibers from spinal nerves C4 through T1, which innervate the arms, shoulders, and hands (4). The spinal nerves from T2 to T11 do not give rise to a plexus, instead forming the intercostal nerves between the ribs (4). Spinal nerves from T12 – L4 recombine in the lumbar plexus, which innervates the back, abdomen, groin, and legs (4). Finally, the sacral plexus emerges from L4 to S4 and connects the buttocks, pelvis, genitals, legs, and feet (4). Of these four spinal nerve plexuses, the brachial plexus and the lumbosacral plexus – a combination of the lumbar and sacral plexuses- are the two major plexuses of the spinal column. Nerves that arise from nerve plexuses play a role in either processing afferent sensory inputs or delivering motor outputs to body parts. 

The spinal nerves intersecting in a nerve plexus further subdivide as they travel throughout the body to provide sensory and motor functions. For example, the spinal nerves that form the brachial plexus first divide into dorsal and ventral rami, the latter of which comprises the roots of the brachial plexus (3). These roots then combine into three “trunks,” with the upper trunk forming from C5 and C6, the middle trunk continuing from C7, and the lower trunk forming from C8 and T1 (3). Finally, each trunk separates into an anterior and posterior division around the first rib, resulting in six divisions that each innervate a different arm area (3). 

Physical injury, cancer, and compression can damage the nerve plexuses and cause various plexus disorders. For example, the brachial plexus can be damaged by an accident that pulls or bends the arm severely (4). Similarly, patients may damage their lumbar plexus from a fall (4). Cancers or other masses, such as tumors or hematomas, can pressure a plexus, resulting in a plexus disorder (4). These plexus injuries may cause numbness or loss of feeling in the body area that receives sensory and motor information from a particular plexus. Luckily, most patients with minor plexus injuries fully recover normal function in due time; however, surgical interventions may be necessary to restore proper bodily function in severe cases (2). 

References 

1. Biga et al. “Spinal and Cranial Nerves.” Anatomy and Physiology, OpenStax, 2019, https://open.oregonstate.education/aandp/chapter/13-3-spinal-and-cranial-nerves/ 
2. Brachial Plexus Injury.” Johns Hopkins Medicine, n.d., https://www.hopkinsmedicine.org/health/conditions-and-diseases/brachial-plexus-injuries 
3. Gilcrease-Garcia et al. “Anatomy, Imaging, and Pathologic Conditions of the Brachial Plexus.” RadioGraphics, vol. 40, no. 6, Oct 1 2020, https://doi.org/10.1148/rg.2020200012 
4. Rubin, Michael. “Plexus Disorders.” Merck Manual Consumer version, Apr 2022, https://www.merckmanuals.com/home/brain,-spinal-cord,-and-nerve-disorders/peripheral-nerve-and-related-disorders/plexus-disorders 
5. Singh, Omesh and YUasir Al Khalili. “Anatomy, Back, Lumbar Plexus.” StatePearls, 7 Aug 2023, https://www.ncbi.nlm.nih.gov/books/NBK545137/