The body is made up of billions of cells.  Cells are the basic unit of all living things.  Cells that make up the nervous system are called neurons.  Neurons allow our brains to learn, reason, and remember.  Through the activity of neurons, the body responds and adjusts to changes in the environment.  A change in the environment is called a stimulus.  The stimuli set off impulses in our sense organs, such as eyes and ears.  Every time you feel something, millions of neurons are "firing" messages to one another.

Neurons are made of dendrites, a cell body (soma), an axon.



There are three different types of neurons:
                                1.  Bipolar
                                2.  Pseudounipolar
                                3.  Unipolar

The smallest neuron is 4 microns wide!  (1000 microns = 1 millimeter)
The longest neuron is from the tip of the toe to the base of the neck.  
To determine the longest sensory neuron in the body:
               -Take ribbon and measure from the tip of the toe to the base of the neck.
 


**Fun fact: There are more neurons in the human brain than there are stars in the Milky Way.**