Interactive neuroscience laboratory

From current to spike

Watch a leaky capacitor become an excitable membrane. The same Hodgkin–Huxley state drives the channel animation, current balance, electrical traces, and state-space projection.

Standalone HTML · runs offline

Membrane mechanism

Channel apertures show population conductance; moving ions show modeled current.
current clampReady
EXTRACELLULAR INTRACELLULAR −65.0 mV membrane voltage CURRENT Iapp 0.0 µA/cm² Na⁺ gNa = 0.0 m³ activation · h availability K⁺ gK = 0.0 n⁴ activation LEAK gL = 0.3 always present CURRENT CLAMP current controlled voltage free to move
The animation represents aggregate membrane conductance and ionic current, not the stochastic opening of individual channel molecules.
Gating statefilled = present · tick = target at current V
m
—
h
—
n
—
Why is voltage changing now?left = hyperpolarizing · right = depolarizing
hyperpolarizingdepolarizing
C·dV/dt = 0.0 µA/cm²

Electrical state through time

The cursor is synchronized with the membrane and state trajectory.

State trajectory

A projection of the evolving system state.
color = hpoint size = m

Voltage dependence of the gates

Steady-state targets x∞(V) and time constants τx(V). The vertical line marks the present membrane voltage.
V = −65.0 mV

Measurement log

Every run you complete is recorded here, so preset-by-preset comparisons do not have to be copied by hand.
Scientific scope, conventions, and references

Model: the active-membrane modes use the classical space-clamped squid giant-axon Hodgkin–Huxley equations with modern voltage signs: Cm = 1 µF/cm², ḡNa = 120 mS/cm², ḡK = 36 mS/cm², gL = 0.3 mS/cm², ENa = +50 mV, EK = −77 mV, and EL = −54.387 mV. The original kinetics were measured near 6.3 °C.

Current convention: ionic current Iion = g(V − E) is outward-positive. Applied current is shown as positive when it contributes to depolarization. The current-balance panel therefore plots each term by its contribution to CmdV/dt.

What is reduced: each channel drawing is a functional population-average conductance. The deterministic gates m, h, and n are not individual molecular doors. The model contains one spatially uniform compartment and therefore demonstrates excitation, not axonal propagation.

Threshold: the page deliberately avoids a permanent threshold line. Whether a stimulus evokes a spike depends on the complete state (V,m,h,n), including recent sodium inactivation and potassium activation.

Primary sources: A. L. Hodgkin & A. F. Huxley (1952), A quantitative description of membrane current and its application to conduction and excitation in nerve; A. L. Hodgkin, A. F. Huxley & B. Katz (1952), Measurement of current–voltage relations in the membrane of the giant axon of Loligo; R. FitzHugh (1961), Impulses and physiological states in theoretical models of nerve membrane.