A bundle of nerve fibers is referred to as a tract in the nervous system. Nerve fibers can also be referred to as a lumbosacral plexus or a complex network of nerves.
Nerve fibers are made up of an endonerium, Schwann cells and axons. While the fibers can have a myelin sheath, Schwann cells can make a covering for an axon without a myelin sheath in the peripheral nervous system. The olfactory nerve fibers are short and do not have a myelin sheath.
The extrapyramidal tracts have long strands that run from the brain to the spinal cord. These tracts play an important role in coordinating motor skills. Depending on the make up of fibers and myelin sheaths, the bundle of fibers can do different tasks.