Teachers TryScience

Getting Connected

Reinforce to students at the beginning of every human body workshop: The human body is made up of many organ systems. All these organ systems work together to make sure our body gets the oxygen we need and waste products like carbon dioxide are thrown out. There are many organ systems- cardiovascular, respiratory, digestive etc. Today we are going to talk about a very important system known as the nervous system.

• Ask students: What happens when you touch a hot pan?
• Tell students: You immediately draw your hand away! This is because pain receptors in your hand send information via nerves to the brain. The brain then sends back a message for your hand to withdraw. This process occurs very quickly and for this we are obliged to our nervous system! The Nervous system is a complex system made up of billions of specialized cells called neurons. Neurons vary in size and shape.
• The nervous system is classified into the central and peripheral nervous systems. The central nervous system consists of the brain and spinal cord.
• The peripheral nervous system consists of the nerves carrying information from the brain and spinal cord to the different parts of the body.

Structure of a neuron:

A neuron is made up of extensions called dendrites, the axonal cell body, axon and the presynaptic axon terminal.

The neuron receives information or messages from other neurons via the dendrites. As shown in the above figure, dendrites are connected to the cell body. The information is then transmitted to the axon. The axon is a single outgrowth extending from the cell body. The axon may or may not have a myelin sheath. Myelination of the axon speeds up conduction of the nerve impulse/message. The impulse then reaches the axonal terminal.

Remember that dendrites bring information to the cell body and axons take information away from the cell body.

Nerve impulse: Information or the message is communicated from neuron to neuron in the form of an electrical impulse.

Now imagine a series of neurons-

The information from neuron 1 is transmitted from the axon terminal to the dendrites of neuron 2 across the small space separating the two. The space is called the synapse. Information is relayed via chemical agents called neurotransmitters. The neurotransmitters are released from the presynaptic terminal upon receipt of the electrical impulse. They travel through the synaptic cleft and transmit the impulse to neuron 2. Synapses maybe axodendritic, axoaxonic etc.

Neurotransmitters may be accepted by the next neuron at a specialized site called a receptor. The action that follows activation of a receptor site may be either depolarization (an excitatory postsynaptic potential) or hyperpolarization (an inhibitory postsynaptic potential). A depolarization makes it MORE likely that an action potential will fire; a hyperpolarization makes it LESS likely that an action potential will fire.

Emphasize: The information travels within a neuron in the form of an electrical impulse but neurotransmission (from neuron to neuron) is via chemical neurotransmitters.

Types of neurons: Three types of neurons occur- sensory, motor and interneurons. Sensory neurons carry

information from the outside recd by receptors to the brain and spinal cord; motor neurons carry information from the CNS to muscles and lastly, interneurons carry information from one neuron to another and are found only in the CNS.

Activity 1: The Model Neuron

Students will learn about the structure of a neuron by constructing a model.

Materials:

• Pictures or photographs of neurons
• Playdough or modeling clay. Provide about a golf ball-sized amount of each of 4 different colors.

Procedures:

1. You will be given 4 different colors of modeling clay or playdough.
2. Build a model of a neuron using different colored clay for the different parts of the neuron.
3. Place your neuron onto a blank paper and then label and draw arrows to the dendrites, soma, axon and axon terminal or your neuron.

Activity 2: Mimicking nerve impulse transmission

• Let's make a chain of neurons...have everyone stand up and form a line. Each person in the line is a neuron. As shown in the figure on the right, your left hand are the dendrites of a neuron; your body is the cell body; your right arm is an axon and your right hand is the synaptic terminal. Your right hand should have a small vial of liquid or some other item, such as a button or pebble, to represent neurotransmitters.
• Each person should be about arms length away from the next person. When the leader says "GO," have the person at the beginning of the line start the signal transmission by placing his or her "neurotransmitter" into the hand of the adjacent person. Once this message is received, this second neuron places its neurotransmitter into the dendrite of the next neuron. The third neuron then places its neurotransmitter into the dendrites of the next neuron and the "signal" travels to the end of the line. The transmission is complete when the "signal" goes all the way to the end of the line.
• Remember that each "neuron" will pass its own transmitter to the next neuron in line. Each neuron HAS ITS OWN neurotransmitter.

Activity 3: Ow!!

Materials:

• Poster papers labeled “Sore foot”, “Neuron Team”, “Neurotransmitter” and “Brain”
• (Make more than one poster boards labeled “Neuron Team” and “Neurotransmitter” to accommodate larger number of students).
• 2 paper signs- Sign #1- Ow! My foot hurts
• Sign # 2- Sit down! You hurt your foot on a nail.

Procedures:

Background: Keep a pan on the table. Ask students to imagine it is hot. What if I were to touch it? Ow!! I immediately draw my hand back.

Ask kids: How did I know it was hot? Who told me to withdraw my hand?

Or

What if there was a nail on the floor and I stepped on it accidentally?

Ow!!

Ask kids: How did I know I got hurt?

Tell students: We are going to find out how we know our hand/foot hurts. Divide kids into the following categories-

1 student represents sore foot at one end and another student represents the brain.

Place the “sore foot” and “brain” students at opposite ends of the room. Select volunteers to represent neurotransmitters. Divide the rest of the students into groups of 3 representing individual neurons. Refer to figure for student placement.

The kid with the sore foot will hold Sign #1 Ow! My foot hurts!

He will pass the sign to the first member of the 3-member neuron, who will then pass it to the other members in sequence. The last member of the neuron team takes the sign, to the neurotransmitter that will pass it to the next neuron.

Message passes via the neuron team to reach the brain. The brain student then hands Sign # 2 to the neuron team and the message is sent back via the same pathway to the sore foot.

• Have a brief class discussion. What have students learned about the nervous system that they did not know before?