2.1 Secrets of the Nervous System

Objective: Describe how the nervous system works to sense, process, and respond to stimuli in the world.

Essential Question: How does the nervous system allow our bodies to interact with the outside world?

The Nerve of Some Systems

Journal Entry📓

You’re listening to some dance music at a party and you first hear the sounds with your ears—using one of your five senses. Those sound waves are input, or stimuli, that are sent through nerves to your brain so you can interpret the signals as music. All input your body receives has to be processed by your brain for you to respond to it. So if you want to get out on the dance floor and move to that beat, your brain sends an output signal that tells your muscles how to move. Your nervous system collects stimuli from your environment, processes it, and decides how to respond to it.

Scenario One

Ethan walks through his house and steps his left foot on a game piece lying on the floor. The game piece is sharp. He quickly lifts his foot and shouts, “Ouch!” Ethan grabs the bottom of his foot with both hands and hops up and down on his right foot.

Scenario Two

Lindsey sees a beautiful, red cardinal bird in the backyard eating food from a bird feeder. Lindsey picks up her camera to take a picture, but the bird is gone when she looks back at the bird feeder.

Scenario Three

Renzo plays his video game while sitting on the couch. He hears his dog barking at the back door. Renzo gets up, walks to the door, and opens it to let his dog outside. He goes back to the couch and continues playing his video game.

The nervous system can be divided into the peripheral nervous system (PNS) and the central nervous system (CNS). Let’s take a look at each of these complex systems and their roles in our gathering, processing, and responding to environmental stimuli.

central nervous system (CNS)✏️

The part of the nervous system that includes the brain and spinal cord.

peripheral nervous system (PNS)✏️

The part of the nervous system that includes nerves and is not part of the brain and spinal cord.

Peripheral Nervous System

Running throughout your body is a complex highway of nerves that are responsible for collecting and responding to stimuli. On one side of this highway is a series of sensory neurons that detect input like tastes, touches, smells, sounds, and sights. They gather these stimuli and send them as signals to the central nervous system.

Once this input is processed in the central nervous system, the brain sends its response as signals down the other side of this neuron highway, through the motor neurons. Motor neurons connect and trigger the muscle cells throughout your body to move, generating necessary responses to the stimuli. In the next activity, you’ll explore how all these signals move through the nerves.

nerves✏️

A bundle of neurons.

sensory neurons✏️

Nerve cells responsible for receiving external stimuli from the body's environment and passing that signal through nerves to the central nervous system.

motor neurons✏️

Nerve cells that pass signals from the brain or spinal cord to a muscle or gland.

Scenario One

Ethan walks through his house and steps his left foot on a game piece lying on the floor. The game piece is sharp. He quickly lifts his foot and shouts, “Ouch!” Ethan grabs the bottom of his foot with both hands and hops up and down on his right foot.

Scenario Two

Lindsey sees a beautiful, red cardinal bird in the backyard eating food from a bird feeder. Lindsey picks up her camera to take a picture, but the bird is gone when she looks back at the bird feeder.

Scenario Three

Renzo plays his video game while sitting on the couch. He hears his dog barking at the back door. Renzo gets up, walks to the door, and opens it to let his dog outside. He goes back to the couch and continues playing his video game.

Using the 3 scenarios from above, describe the types of input the peripheral nervous system receives in each of the three scenarios.

Central Nervous System

The central nervous system includes the brain—the control center for your entire body—and the spinal cord. Once the signals sent by the sensory neurons of the peripheral nervous system reach the central nervous system, the brain processes that input, and if necessary, makes a decision to do something about it.

In the introductory example, your brain made a decision to dance after processing the sound of the music. When the brain decides to move a part of the body or respond to environmental stimuli, the central nervous system sends a signal through motor neurons, which tell the body’s muscles to move or dance.

Scenario One

Ethan walks through his house and steps his left foot on a game piece lying on the floor. The game piece is sharp. He quickly lifts his foot and shouts, “Ouch!” Ethan grabs the bottom of his foot with both hands and hops up and down on his right foot.

Scenario Two

Lindsey sees a beautiful, red cardinal bird in the backyard eating food from a bird feeder. Lindsey picks up her camera to take a picture, but the bird is gone when she looks back at the bird feeder.

Scenario Three

Renzo plays his video game while sitting on the couch. He hears his dog barking at the back door. Renzo gets up, walks to the door, and opens it to let his dog outside. He goes back to the couch and continues playing his video game.

Using the 3 scenarios from above, describe the types of output the central nervous system initiates in each of the three scenarios.

Map a Trip Through the Nervous System

It’s your turn to diagram the nervous system. You’ll draw and label the primary body parts that make up the nervous system, and then draw the path of input and output signals for the sense you are assigned.

Draw a body diagram (like the one pictured to the right).
Draw and label the following items on each body diagram.

- central nervous system
  - brain
  - spinal cord
- peripheral nervous system
  - nerves

Draw the path of input and output signals for the sense you were assigned and create a scenario for your sense. Now that your diagram is all set up, you’ll complete the following:

Use a colored pencil to draw lines showing where the input signal(s) starts and ends.
Draw arrows along the lines to show which direction the input signal(s) is traveling.
Use a different colored pencil to draw lines that show where the output signal(s) starts and ends.
Draw arrows along the lines to show which direction the output signal(s) is traveling.
On your diagram, create a key or legend to show which color represents the signal moving through sensory neurons and which color is the signal moving through the motor neurons.

Recall the dancing to music scenario you read about at the beginning of this activity. Here's an example of what that scenario's diagram may look like. It shows the music stimulus being transferred as a sensory signal to the brain and motor neurons sending a signal to the muscles for dancing.

Conclusion Questions

How do our bodies receive stimuli as input, and what part of the nervous system is responsible for that process?
How does the entire nervous system allow our bodies to interact with our world? Your response must include the following terms:
1. - peripheral nervous system
  - central nervous system
  - sensory neurons
  - motor neurons
How do you think a problem with the sensory or motor neurons might affect your body?