This applet simulates the Noble model in a 1D cable or 1D ring of any length between 0.5 cm and 27.5 cm. Initiation by a stimulus, propagation, and complex dynamics such as discordant alternans can be studied. To learn more about the model in single cell, use the Noble single cell applet. Note: since the Noble model is auto-oscillatory with its original parameter settings, here gna is decreased from its original value of 0.14 to 0.12 to make the system excitable.

Features:

• The Start button initiates the applet. An action potential can be produced either by pressing the Apply S1 button or by clicking inside the panel with the mouse, which will produce a stimulus that will generate an action potential if large enough.
• The length can be changed at any time by using the Cable Length slider. The new length is automatically indicated on the horizontal axis (minimum length is 0.5 cm, maximum is 27.5 cm).
• To observe AP initiation and propagation in more or less detail, the simulation speed can be increased or decreased at any time by using the Simulation Speed slider.
• When initiating a stimulus using the Apply S1 button, attributes of the stimulus can be set by using the Strength, Duration, Length, and Position text boxes.
• The list box in the bottom left corner is used to choose either a cable or a ring simulation. Note: using a long cable before changing from a cable to a ring is recommended to prevent self-termination of the wave.
• The gna, gnac and gs text-boxes are used to set the sodium and potassium conductances used in the simulation.
• The check boxes on the right indicate which variables are plotted.
• The Reset button brings the membrane potential of all the cells back to the rest state.
• The Stop button is used to stop the simulation at any time. The simulation can be resumed by using the Continue button that replaces the Stop button when the simulation is stopped.

Suggested Experiments:

• Click the Start button and then the Apply S1 button to generate an action potential propagating to the right. When the wave front is close to the right boundary, click the Stop button and use the list box in the lower left corner to change the cable to a ring, then click the Continue button. This allows the wave to reenter, and after a few rotations around the ring it will be a steady wave with a fixed wavelength. Decrease the ring size slowly, and observe the formation of discordant alternans at a length of 10 cm and conduction block leading to wave termination at a length of 8.6 cm.
• Repeat as above, but change the sodium and/or potassium conductances and find the lengths at which alternans appear.
• Reset using the Reset button and study the threshold for excitation as a function of the stimulus parameters (strength, duration, and length) as well as the sodium and potassium conductances.
• Induce multiple waves by clicking inside the window with the mouse. Each time the mouse is clicked, a voltage stimulus proportional to the height of the mouse position within the simulation window is added to the voltage at the location of the mouse along the cable. Try to induce a single reentrant wave along a ring.

The model can be found in the following reference: D Noble, J Physiol 1962; 160: 317-352.