ATV Brake Cables usually have two parts. The inner wire is made of twisted strands of steel. The outer housing is also made of flexible steel, usually wound in a spiral. The inner wire runs down the middle of the housing. Both parts are equally important, neither can work without the other.
Isaac Newton said "For every action, there is an equal and opposite reaction." In the case of some cables, this means that there cannot be a pull on an inner cable without an equal push on the housing.
To save weight, many ATVs substitute the frame for some sections of the housing. This is done by attaching "cable stops" to the frame or fork. A cable stop has a socket to receive an end of a cable housing, and a small hole or slot through which the inner cable can pass, but the housing can't. The "push" of the housing is transferred to the frame, so the inner wire can run bare until it gets to another cable stop facing the other way, where the "push" from the frame is transferred back to another length of housing.
This "bare cable" routing can be done anywhere that the cable runs in a straight line, and doesn't have to bend. Housing must be used from the handlebars to the frame, to accommodate the turning of the handlebars as the ATV is steered. Lengths of housing are also commonly used when the direction of pull of the cable must be changed.