Although blood vessels and nerves both aim to move something from here to there, their structures are different owing to their varying functions. Blood vessels, as their name implies, move blood, while nerves move electrochemical signals. Whether you’re a first-year biology student or an expert working on your Ph.D., knowledge of how vessels and nerves differ is a must.
The circulatory system is a closed network that starts and finishes in the heart. This means that all vessels, whether arteries, capillaries or veins, participate in one vast network of blood transport. Larger arteries and veins move blood toward and away from the heart, while capillaries introduce it to surrounding tissue. In all cases, blood eventually travels back to the heart to be reused. Nerves, however, are not all connected to one another. Many interconnect in the brain, as do nerves in the body when they transfer signals across long chains of nerves until they reach the brain. However, the nervous system is not entirely closed as it is with vessels.
Both vessels and nerves are long and thin, sometimes microscopically so, but you easily can tell them apart by looking at surrounding structures. Arteries carry blood away from the heart, becoming smaller and ending eventually in tiny capillaries. As blood returns to the heart, it travels in veins, which get larger and larger. Nerves, however, have long tails with huge heads, or somata, out of which sprout dendrites, which look like hairs. At their other end they have a terminal bundle, which is a collection of fine, branching structures that transmit signals to the next nerve in the chain using chemical neurotransmitters.
Although both nerves and vessels are long and thin, the way cells are organized is vastly different. Blood vessels are composed of many cells grouped in many layers on top of one another to form the vessel walls. Therefore, the extended length of a blood vessel is the result of huge numbers of cells next to one another. In a nerve, however, a single cell may be as long as 3 feet.
Within blood-carrying structures like veins and arteries, blood moves through pressure created by the heart’s beating. Because of this, vessels are constructed as hollow tubes in which blood is contained. Nerve signals move in a different way, by propagating along the nerve cell’s long axon. The signal is received by the dendrites in the cell body, and is then transmitted along the length of the neuron. Although this occurs inside a myelin sheath that coats the outside of the cell, the axon is not a hollow tube, but rather carries the signal along its body.