Nerves and veins are two components involved in the transportation of different elements in the animal body. Nerves belong to the nervous system while veins are a component of the circulation system. The main difference between nerve and vein is that nerve is an axon bundle of neurons in the peripheral nervous system, which carries nerve impulses whereas veins are blood vessels, which return deoxygenated blood towards the heart. Both nerves and veins vary in size. Ideally, both nerve and vein carry corresponding things in one direction excluding the mixed nerve. The constriction and dilation of veins are coordinated by autonomic nervous system.