The Nervous System

There are 3 kinds of nerves in the nervous system. Motor nerves are in charge of moving the body through voluntary and involuntary actions. Sensory nerves are in charge of picking up information from the senses. Connecting nerves connect the sensory and motor nerves to the brain and spinal cord.

For instance, you smell a flower, and the sensory nerves in your nose tell your brain, via the connecting nerves, that you smell the flower. However, sometimes the sensory signals do not go up to your brain. These are called reflexes. Say there is a bee coming by, flying right at your eye. Your eye blinks to protect the eye without you thinking about it. This is because if you did think about it, it would take too long. A reflex signal goes from sensory nerves, through connecting nerves to the spinal cord, then quickly back through connecting nerves to motor nerves that make you blink.

Sensory nerves are all over your body, but you have more in some places than in others. We did an experiment to show this. We opened a paperclip so that it had two points. Placing the points on the wrist, we recorded how many points were felt, either one or two. The feeling changed as the points were bent farther apart. Then we tried a fingertip and knee. Here are the results:

Body Part	Point Distance	# Felt
Wrist	0cm	1
	0.5cm	1
	1cm	1
	1.5cm	2
	2cm	2
Finger	0cm	1
	0.5cm	2
	1cm	2
	1.5cm	2
	2cm	2
Knee	0cm	1
	0.5cm	1
	1cm	1
	1.5cm	1
	2cm	2

We discovered some interesting things in this experiment. The finger has more sensory nerve cells close together than does the wrist or knee. This makes sense because we use fingers to feel things.