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Crossing the Synaptic Gap

Crossing the Synaptic Gap

TEM image showing the synaptic gap (hot pink) between two neurons.
© Dennis Kunkel Microscopy, Inc.

  • Grades:
  • Length: 60 Minutes


Students conduct a simulation to demonstrate how multiple incoming signals influence the action of neurons.

This activity is from the Brain Chemistry Teacher's Guide. Lessons in the guide are designed for use with students in grades 6–8, but they also may be used with other grade levels as appropriate.

Teacher Background

Most neurons in the brain communicate with each other by releasing chemical messengers called neurotransmitters. Neurotransmitters cross the gaps between neurons or between neurons and other cells, such as muscle, and match up with specific receptors. Chemical signaling between neurons allows different kinds of messages to be sent. For example, some chemical messengers stimulate neurons to fire, while other messengers make it harder for an electrical impulse to be generated in the receiving neuron. Since one neuron can share synapses with thousands of other neurons, the combined effects of different messages ultimately determine whether a signal will be triggered or not.

Many drugs interfere with communication between nerve cells. Some drugs act directly on neurons, neurotransmitters and receptors. Curare, for example, is a deadly poison used by South American Indians. It causes death from paralysis by blocking receptors on muscle cells. Since the receptors are blocked, the real chemical messenger for muscle contraction (acetylcholine) can no longer stimulate the muscles to contract.

Drugs also can interfere with communication between neurons in other ways, such as by preventing the manufacture or release of neurotransmitters, by causing excessive firing of neurons by stimulating
massive releases of neurotransmitters, by mimicking the effects of chemical messengers, or by preventing the normal breakdown and recycling of chemical messengers.

This activity will help students learn about the relationships between chemical messengers, receptors and the actions of common chemicals in alcoholic beverages, cigarettes and illicit substances on brain functions.

Objectives and Standards


  • Neurotransmitters can either stimulate the next neuron to send a signal or inhibit that neuron from sending a signal.

  • Certain chemicals change the way signals are sent and received.

Science, Health and Math Skills

  • Predicting

  • Comparing and contrasting

  • Recording observations

  • Interpreting results

Materials and Setup

Teacher Materials

  • 6 sheets of card stock

  • Document projector (or overhead projector and transparency of “Transmitters & Receivers,” page from the activity, “What Is a Neuron?”

Materials per Group of Students

  • 1 square, 6-sided, numbered die

  • Prepared set of “Brain Chemical” cards

Materials per Student

  • Copy of “Fire Those Neurons!” student page


  1. Make six photocopies of “Brain Chemical Cards” on white card stock. Cut out the cards to make six sets of the four different cards. Each group should receive one set of cards.

  2. Make 24 photocopies of the “Fire Those Neurons!” page (one per student).

  3. Have students conduct this activity in groups of four.

Procedure and Extensions

  1. Review the steps in nervous system communication that students learned while playing “Locks & Keys” (see the activity, “Message in a Neuron”). Tell students that they will be simulating what happens when chemical messengers, or neurotransmitters, go from one neuron to the next. Point out that most neurons can receive messages from many other neurons. Some of these messages “stimulate” or cause firing, other messages “inhibit” or prevent firing. Neurons “decide” to fire or not depending on the kinds of messages they receive.

  2. Distribute a copy of “Fire Those Neurons!” to each student.

  3. Students in each group will take turns rolling a die twice. The first roll will determine how many incoming signals excite the neuron to fire. The second roll will determine how many signals inhibit firing (or have students use two different colored die and roll them together). During each trial, students should subtract the second number from the first. If the outcome is zero or a positive number, the neuron will “fire” or pass the message. If the outcome is a negative number, the neuron will not fire. Have students conduct at least four trials, so that each student collects data on his or her sheet.

  4. Conduct a class discussion of the results of the model thus far. Ask, Did it matter how many “stimulating” messages were present for firing as long as the number was greater than the “stopping” or “inhibiting” messages? Point out that the firing of a neuron is like turning on a light switch—either an impulse is created or it is not.

  5. Tell students that they will be conducting another round of the simulation. This time, however, give each student a “Brain Chemical” card with additional instructions for each trial. Have students take turns investigating the effects of each brain chemical. As they progress through the simulation, students will discover that the drugs have changed the patterns of neuron firing.

  6. After students have completed the second round, ask, Did you receive different results this time? Did the neurons fire more or less often? Did the responses of the neurons change over time? Help students conclude that each of the chemicals on the Brain Chemical cards changes the way neurotransmitters work. In addition, at least two of the examples (cocaine and inhalants), cause changes in neurons. Revisit the neuron diagram (“Transmitters & Receivers,” from the activity, “What Is a Neuron?”) to find the places affected by these chemicals.

  7. Conduct a class discussion to help students correlate the effects of drugs on the nervous system to physical or behavioral changes that can be observed or felt. Detailed information about the substances listed on the “Brain Chemical” cards are given in the box, “Commonly Abused Drugs.” For additional information on other substances, read “Drugs and the Nervous System” (see PDF).


Encourage students to learn more about how different chemicals affect the brain by conducting research in the library on the Internet. A good place to start is the National Institute on Drug Abuse (

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NIH Blueprint for Neuroscience Research Science Education Award, National Institute on Drug Abuse, and NIH Office of the Director

The Learning Brain: Interactive Inquiry for Teachers and Students
Grant Number: 5R25DA033006

Science Education Partnership Award, NIH

Filling the Gaps: K-6 Science/Health Education
Grant Number: 5R25RR013454