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In many cases, a neuron's axon can be very long, and as such is known as a nerve fiber. Giraffes have single axons several meters in length running along the entire length of the neck and a human motor neuron can be over a meter long, reaching from the lumbar region of the spine to the toes. However, some neurons have axons that are very short and even absent. Axons are the primary transmission lines of the nervous system.
The enormity of the Great Pyramid poses a challenge for any who would attempt to explain how it could have been constructed. It is estimated to comprise some 2.4 million stone blocks averaging 2.5 tons (2.27 metric tons) each, plus additional blocks weighing considerably more lying deep within the pyramid where they serve special functions. Its height when new, 480.9 feet (146 m), would have been within 74 feet (21.3 m) of the top, 555 feet (169.7 m), of the Washington Monument in Washington, DC, which was built 4,444 years later. A number of alternative theories have been proposed to explain how the Great Pyramid was built.