Neuron Beach

One neuron drawn as a coast. Waves come in over sandbars, fill a pool, spill through a sluice, and the backwash runs back over the sand that made it spill. Click a sandbar to send a wave.

soma pool (membrane potential) tuft hot zone (Ca²⁺) spill = spike tide

Send waves

Teach

Wait for the tideFootprints stay soft until the tide fixes them (three-factor rule). Off: they set at once (plain STDP).

The beach Marsh in the dendrites

Fast ripples die in the marsh: friction in shallow water, wide flats that must fill and drain, seepage into the sand. In a dendrite these are axial resistance, membrane capacitance and leak.

Berm height (threshold) Berm keeperEach spill raises the berm a little; it settles back slowly (homeostasis). Waves keep comingRandom waves on all shores. Speed

Readings

Things to try

Send one wave at A. The pool rises and falls back. One swell is below the berm.
Press A + B + C. Together they fill the pool past the berm: the sluice opens, a big wave runs down the axon and a backwash runs up all three beaches.
Press Ripple at B, then Wave at B. Same strength, but the ripple dies in the marsh. Raise the marsh slider and even swells fade.
Press Far shore alone: the hot zone fills a little and nothing else happens. Press A + B + C and then Far shore straight away: the backwash meets the far wave, the hot zone ignites and the pool spills several times in a row. That is a burst.
Press Pair A with a burst four or five times. Watch sandbar A open up. Then a wave at A alone makes the pool spill.
Tick Wait for the tide and pair again: the footprints glow but the sandbars don't move until you press Tide comes in. Wait too long and they dry out.
Turn on Waves keep coming and Berm keeper. The berm climbs when the pool spills a lot, and the high lake drains if it spills too fast.

What each part is

On the beach	In the neuron	What it does here
Waves	Voltage and current	The signal. Height of the water is the potential.
Sandbar at a channel mouth	Synapse strength (weight)	A deeper, wider mouth lets more of each wave in.
Marshy shallow channel	Dendrite (cable)	Low-pass filter: fast ripples die, slow swells reach the pool.
Soma pool	Soma membrane potential	Adds up what arrives; drains slowly when nothing comes.
Berm and sluice	Axon initial segment (Na⁺ channels)	When the pool reaches the berm, the sluice opens once, then stays shut for a moment (refractory period).
High lake behind the dunes	Ion gradients, kept by the Na⁺/K⁺ pump	The spike's energy comes from here, not from the incoming waves. Spill too fast and it runs low.
Narrow channel with walled banks	Axon with myelin	Walls stop seepage, so the wave stays sharp and fast.
Wave machines along the channel	Nodes of Ranvier	Each one re-lifts a passing crest so it arrives full size.
Backwash	Back-propagating action potential	The spill also sends a wave back up every dendrite.
Wet footprint	Eligibility / presynaptic trace	A wave that just came in leaves soft sand at its mouth for a while.
Backwash meets a wet footprint	Spike-timing plasticity (LTP)	The mouth deepens. A wave that arrives just after a spill makes it shallower (LTD).
Tide	Dopamine and other neuromodulators	One signal for the whole beach: fixes soft footprints that are still wet.
Far shore and hot zone	Apical tuft and Ca²⁺ spike zone	Too far to fill the pool alone. With the backwash at the same time it ignites and the pool bursts (Larkum's BAC firing).
Berm keeper	Homeostatic plasticity, AIS shift	A busy pool gets a taller berm; a quiet one a lower berm.
Weak ping	Sub-threshold probe	Feels the sandbars without moving them: no spill, no backwash, no write.

A toy, built to be seen. The water is a linear shallow-water network on a graph of cells; the sluice, hot zone, wave machines and sandbar rules are designed switches, not ion-channel models, and the numbers have no units. Genes, the builder that decides what kinds of sand and berm a beach can have, are not in the simulation at all.