This computer simulation allows students to explore some of the most important functions of nerves: how the membrane potential is altered, how action potentials are produced, and how a specific nerve integrates the hundreds of inputs that it receives. There are a total of 4 modules in this simulation. Each module looks at a different aspect of nerve function. Students are expected to "play" with the simulations. Questions are included to guide students' inquiry.

Module 1: nerve function: an overview

This first module provides an overview of the structure/function of the nerve from the histologic level to the molecular. The model begins with a view of axons making contact with a cell body. The simulation gives students a visual model of the various levels of detail which they can and should be envisioning the neuron.

Module 2: nerve function: the synapse

This model demonstrates events at the synapse when neurotransmitter binds to its receptor. The initial setting shows a large number of Na, K, Cl ions and negatively charged protein molecules distributed throughout the cytoplasm and the extracellular fluid. The student can control the amount of neurotransmitter that is released into the synaptic cleft. Graphical displays depict changes in the number of Na ions that move across the cell membrane. This simulation is designed, in part, to combat the common misconception that the intracellular sodium concentration changes dramatically as sodium ions "rush" across the membrane during an action potential.

Module 3: nerve function: signal integration This model contains the cell body of a neuron on which there are eight neural inputs. Four of these inputs are excitatory and four are inhibitory. There is a "slider bar" connected to each neuron that the student can use to determine the discharge rate for each input, independently.

Using various combinations of inputs, the voltage can be altered at the axon hillock where voltage-gated channels in the trigger zone can be activated. In order to trigger an action potential, the trigger zone of most neurons needs to depolarize to about 45 mV. The value displayed near the axon hillock in the animation is a measure of the voltage at the trigger zone. Using this model, students will discover that triggering action potentials is not quite as straightforward as one might imagine.

Module 4: nerve simulation: action potentials This module depicts an axon, beginning near the axon hillock. Following directly on module 3, the simulation allows students to directly effect changes in voltage at the axon hillock and to observe the consequences of those changes.

This set of Flash modules represents an approach to the simulation of physiological processes that is visually, rather than mathematically oriented. Participants can benefit from the technical and pedagogical issues that we faced during development.

Franz Sugarman
S2 016 Schurman Hall
Cornell University
Ithaca, NY 14853
Phone: 607-253-3768
Fax: 607-253-3709
Email: fs47@cornell.edu

CO-AUTHORS:
Richard Rawson
T8-008C Vet Res Tower
Cornell University
Ithaca, NY 14853
Phone: 607-253-3748
607-253-3854
Fax: 607-253-3851
Email: rer1@cornell.edu
Website: http://web.vet.cornell.edu/authors/rer1/myHome/index.htm