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The Neuron- Up Close and Personal

The Question of Intelligence






*Here are some interesting facts and statistics about neurons in humans and other animals:

Average number of neurons in the human brain= 100 billion
Average number of neurons in an octopus brain= 300 billion
Rate of neuron growth during development of a fetus (in the womb)= 250,000 neurons/minute
Diameter of a neuron= 4 to 100 microns
Longest axon of a neuron= around 15 feet (Giraffe primary afferent axon from toe to neck)
Velocity of a signal transmitted through a neuron= 1.2 to 250 miles/hour

(remember that these are averages because there is lots of variability in the nervous system!!)

Guess what? There are more nerve cells in the human brain than there are stars in the Milky Way.

What if we lined up all the neurons in our body? How long would that line stretch?


Well, let's think about this... Let's assume that one neuron is about 10 microns long. Remember, this is just an example, because neurons come in all different sizes. So, if we line up 100 billion neurons which are 10 microns long . . .

100,000,000,000 neurons x 10 microns= 1000 km or about 600 miles!

This may help with the math:
1000 microns= 1milimeter (mm)
10 mm= 1centimeter (cm)
100 cm= 1 meter (m)
1000 m= 1 kilometer (km)

Go to discussion of intelligence

Huh? Can we start over?

Click in a box below for more information about neurons and the nervous system
Do all brains of all animals have neurons??
What does a neuron look like and how does it work?

*(see bibliography for sources of these statistics, particularly www.soton.ac.uk)