A nerve cell (a neuron) picks up nudges on its dendrites, fires a signal along its axon and passes it on with a chemical that crosses a gap, the synapse. A labelled neuron diagram shows the parts. It cannot show a signal fire, jump along the myelin or cross the gap. Put this on the board and the class can watch one nerve cell at work, from the dendrites to the end knobs, then zoom into the gap to see how the message reaches the next cell.
Fire it: pick a weak or a strong nudge and press Fire, or press the dendrites. A weak nudge fades away and nothing is sent. A strong one sends a signal, and a line beside the model shows every signal is the same size. Hold Fire to send them more often. Take the myelin away and the signal crawls; two bars show how much longer it takes. Predict first: step 4 asks the class whether the signal will be faster, slower or the same without myelin, before Show me. Zoom into the gap at step 6. Press a name to zoom in on that part and read about it, press Labels once for a quiz where every name hides behind a ?, slow it down, turn the model by dragging, and Share a link that opens it just as you left it.
The reflex arc simulation shows the whole route a message takes, from the fingertip to the spinal cord and back to the arm. This one zooms in on a single nerve cell on that route: what the signal is, why myelin makes it fast, and how it crosses the gap to the next cell. Use the reflex arc first, then this.
On Simple the board says nerve cell, signal and gap. Textbooks say neurone (neuron in the United States), nerve impulse or action potential, and synapse. They mean the same things. The rest match up like this. The bare gaps between the myelin sleeves are the nodes of Ranvier, and the signal jumping from one to the next is saltatory conduction. The level a nudge has to reach before the cell fires is the threshold, and weak nudges adding up to reach it is summation. The chemical messenger is a neurotransmitter, the end knobs are the synaptic knobs or axon terminals, and the cells that wrap the axon in myelin are Schwann cells. Press More detail, top right, to put these names on the model itself: nodes of Ranvier, a Schwann cell, axon terminals and the synapse, with the neurotransmitter and receptors in the close-up of the gap.
The words are pitched at ages 11 to 16: Years 7 to 11 in England, 6th to 10th grade in the United States. In England it fits AQA GCSE biology 4.5.2.1 (neurones and the synapse in the reflex arc), and AQA A-level biology 3.6.2.1 and 3.6.2.2 (nerve impulses, all or nothing, myelination and the synapse).
Why are myelinated neurons faster?
Myelin wraps the axon in separate fatty sleeves with small bare gaps between them. The signal can only happen at the bare gaps, so it jumps from gap to gap instead of creeping along every bit of the axon. That makes it many times faster: about 1 metre a second without myelin, up to about 100 with it. Myelin makes the signal faster, not bigger.
How does a signal cross a synapse?
It does not jump the gap. When the signal reaches an end knob, tiny sacs release a chemical messenger. The chemical drifts across the gap and fits into receivers on the next cell, which starts a new signal there. Then the chemical is cleared away. The two cells never touch.
What does all or nothing mean?
A nerve cell either sends a signal or it does not. Too weak a nudge does nothing. A strong enough nudge sends a signal, and every signal is the same size. A stronger nudge sends signals more often, never bigger ones.
Why do messages only go one way?
Only the end knobs can release the chemical, and only the next cell has the receivers to catch it. So in your body a message passes from one nerve cell to the next in one direction.
What does the simulation show?
One whole nerve cell (a motor neurone): branching dendrites, a cell body with its nucleus, one long axon wrapped in myelin sleeves, and end knobs. Press Fire to send nudges, switch the myelin on or off, and zoom into the gap to watch the chemical cross.
What has been simplified?
A few things, on purpose. The cell is not to scale: a real axon can be a metre long. In the model, weak nudges add up as a simple sum that fades, and the speed difference with and without myelin is smaller than in a real cell. A motor nerve cell's body really sits inside the spinal cord; only the axon leaves it.
What age is it for?
The words are pitched at ages 11 to 16. It also works as a starter at A-level.
Is it free?
Free to try. Opening Science Simulations uses one token for the whole day, however many times you come back to it. Every account gets 20 free tokens, and Pro gives 50 a day.
The reflex arc simulation shows the whole route this cell sits on, and the interactive brain model shows where billions of nerve cells work together. All twelve are on the Science Simulations page. For models the class can spin, from skeletons to dinosaurs, try 3D Explorer.