A plexus is like an electrical junction box in a house. In a plexus, nerve fibers from different spinal nerves are sorted and recombined, so that all fibers going to a specific body part are put together in one nerve.
Four nerve plexuses are located in the trunk of the body:
The cervical plexus provides nerve connections to the head, neck, and shoulder.
The brachial plexus provides connections to the chest, shoulders, upper arms, forearms, and hands.
The lumbar plexus provides connections to the back, abdomen, groin, thighs, knees, and calves.
The sacral plexus provides connections to the pelvis, buttocks, genitals, thighs, calves, and feet.
Because the lumbar and sacral plexuses are interconnected, they are sometimes referred to as the lumbosacral plexus.
The spinal nerves in the chest do not join a plexus. They are the intercostal nerves, which are located between the ribs.