If a human brain were to be unraveled and stretched out completely, how long would it be?

If you mean the cerebral cortex, sources suggest that if stretched out the cerebral cortex would be 0.23 sq. m or 2.5sq.ft.

The brain is the center of the nervous system in animals. All vertebrates, and the majority of invertebrates, have a brain. Some "primitive" animals such as jellyfishes and starfishes have a decentralized nervous system without a brain, while sponges lack any nervous system at all.

It consists of approximately 100 billion neurons (which is as many cells as there are stars in the Milky Way). Each neuron has somewhere between 1,000 and 10,000 synapses, equaling about 1 quadrillion synapses.

As per Randomhistory.com, if all the neurons in the human brain were lined up, they would stretch 600 miles.

How well do you know your amazing brain? Test your smarts by answering these superfun quiz questions from Nationalgeographic.com.