According to Neurogenetics at the University of Tennessee Health Science Center, the human body has 95 to 100 billion neurons or nerve cells. The brain alone has at least 85 billion of these cells, although estimates go as high as 1 trillion.
While humans have about 100 billion nerve cells in their bodies, other mammals, such as blue whales, boast at least twice that number. The University of Tennessee points out that the elephant's brain is about three times as big as that of a human and contains about three times as many nerves.
The Univeristy of Washington explains that nerves are divided into three groups: sensory neurons, motor neurons and interneurons. While sensory neurons send information to the central nervous system, motor neurons send information away from the central nervous system. For example, information picked up from the nose and ears, like smells and sounds, travels through sensory neurons to the brain. Interneurons connect the sensory and motor neurons.
Nerve cells are very similar to regular cells, the University of Washington says. They contain a cell membrane and a nucleus with genetic material and organelles, and they undergo basic cellular processes. However, they differ from other cells in distinct ways. Nerve cells have dendrites and axons, which transfer electrical signals to and from the central nervous system. Also, nerve cells are usually not replaced like other cells in the body. The older a human being gets, the fewer neurons he has, although there is some evidence that new neurons can grow in adults.