Spinal Cord.
a tract is a bundle or group of nerve fibers located within the brain or spinal cord
It is a bundle of nerve fibers that carry electrical impulses to the brain from the retina.
The thick bundle of nerve fibers through which the brain communicates with the body is the spinal cord.
The bundle of the nerve fibers is a collection of the threadlike extension of the nerve cell that consists of the myelin sheath and axon in the nervous system. There are nerve fibers in the peripheral nervous system and the central nervous system.
VASICLES
Nerve cells called neurons sends messages from brain to body along fibers called axons.
A bundle of nerve fibers is surrounded by perineurium, a connective tissue that wraps around them.
I also think that you may be thinking of how one half (or one side) of the brain carries messages to the other side. That is done with a wide, flat bundle of neural fibers called the corpus callosum.
This bridge is a large bundle of nerve fibers called the corpus collosum.Corpus Callosum
the corpus callosum
nerve
The corpus callosum is the bundle of nerve fibers that connects the two hemispheres of the brain, allowing communication between them.