Teacher guides

Everything you need to run each lesson without any training: a 45-minute plan, what students should notice, the answers to expect, and a worksheet to print.

Lesson 1
How a fly remembers a smell
Students trace a smell from the receptors to the cells that read its memory, and show that silencing one layer of a pathway cuts off everything after it.
Teacher guide Student worksheet Show it to the class
Lesson 2
How a fly knows which way it’s facing
Students see that a ring of neurons holds the fly’s heading as one patch of activity, and that inhibition from the ring neurons keeps that patch in place.
Teacher guide Student worksheet Show it to the class
Lesson 3
The 30-millisecond escape
Students follow a reflex from the eyes to the leg muscles in about 30 milliseconds, and show that the fast escape depends on one link, the giant fiber.
Teacher guide Student worksheet Show it to the class

A companion course

In Israel, many students on the 5-unit biology track also take Tel Aviv University’s free course The Brain: the Most Wonderful Machine of All (opens in a new tab) on Campus IL, taught by Prof. Yossi Yovel and Prof. Yaniv Assaf. It teaches neurons, action potentials, and synapses in depth, and these lessons make a hands-on companion to it. WiredMind is an independent project. It is not affiliated with the course, the university, or Campus IL.

Key terms

Basic terms

Neuron: A nerve cell. It receives signals from other cells and, when enough of them add up, sends a signal of its own.
Action potential (spike): A brief electrical pulse that an active neuron sends along its length, also called a spike or an action potential. In the lessons, each flash of light marks one.
Synapse: The junction where one neuron passes its signal to the next. The more synapses two cells share, the stronger the link between them.
Neurotransmitter: A chemical that a neuron releases at a synapse to pass its signal on. Some neurotransmitters excite the next cell, and others inhibit it.
Excitation: A signal that pushes the next neuron toward firing.
Inhibition: A signal that holds the next neuron back from firing. A network needs it to stay stable and precise.
Acetylcholine: The main excitatory neurotransmitter in a fly’s brain. In the lessons, cells that release it excite the cells they connect to.
GABA: An inhibitory neurotransmitter, in flies and in people. In the lessons, cells that release GABA quiet the cells they connect to.
Neural circuit: A group of neurons wired together to do one job, such as recognizing a smell or setting off a jump.
Connectome: A complete wiring diagram of a nervous system: every neuron and every synapse between them. The lessons run on the connectome of one real fruit fly.
Stimulate: The lesson’s button that makes one group of cells fire for a moment, much as scientists switch chosen cells on with light.
Silence: The lesson’s button that stops one group of cells from firing, to show what the rest of the circuit does without them.

Lesson 1 · How a fly remembers a smell

Antennae: The two feelers on a fly’s head. A fly smells with them, the way you smell with your nose.
Smell receptors: Nerve cells on the antennae that fire when a smell lands on them. Every smell starts here.
Antennal lobe: The first stop for smells inside the fly’s brain, where the smell receptors hand their signal to the projection neurons.
Projection neurons: Nerve cells that carry the smell signal from the antennal lobe deeper into the brain, to the mushroom body.
Mushroom body: A mushroom-shaped part of an insect’s brain where smells are sorted and smell memories are stored.
Kenyon cells: The small nerve cells of the mushroom body. Each smell switches on a different handful of them, so every smell gets its own pattern.
Output neurons: Nerve cells that read the pattern of the Kenyon cells and pass it on to the rest of the brain. Scientists call them MBONs, short for mushroom body output neurons.

Lesson 2 · How a fly knows which way it’s facing

Turn neurons: Nerve cells that fire when the fly turns and push the bump around the compass. Scientists call them P-EN2 neurons.
Compass neurons: A ring of nerve cells that keeps track of which way the fly is facing. Scientists call them E-PG neurons.
Activity bump: The patch of active compass neurons. Where it sits on the ring shows which way the fly is facing.
Ring neurons: Nerve cells that bring what the fly sees, such as landmarks, to the compass. They quiet the compass neurons, and that holds the bump in place.
Landmark: Something the fly sees that stays in place, like the sun or a tree. The fly uses it to keep its sense of direction steady.
Protocerebral bridge: A bar-shaped part of the fly’s brain, the protocerebral bridge. The compass neurons and the turn neurons both run through it.

Lesson 3 · The 30-millisecond escape

Looming neurons: Nerve cells behind the fly’s eyes that fire when something grows quickly in view, like a swatter coming closer. Scientists call them LC4 and LPLC2.
Giant fiber: A very thick nerve cell that runs from the brain down into the nerve cord. It carries the fly’s fastest escape signal. A fly has two, one on each side.
Nerve cord: The fly’s version of a spinal cord: a bundle of nerve cells in its chest that controls the legs and wings.
Jump neurons: Motor neurons that make the jump muscles of the middle legs contract, so the fly springs into the air.
Reflex arc: The route a reflex takes: from sensory neurons, through one or more relay cells, to the motor neurons that move a muscle.
Sensory neuron: A neuron that picks up something from the world, such as light or a smell, and reports it to the brain.
Motor neuron: A neuron that carries a command out to a muscle and makes it contract.
Electrical synapse: A direct channel between two neurons that passes a signal with almost no delay. The map behind the lessons records chemical synapses only.