Computing and the Brain Biological Neural Networks Tutorial 1

Action Potentials, Synapses and Model Neurons

Give short answers to the following.

Question 1: How is an action potential generated?

In answering this question, define the meanings and roles of:

threshold sodium (Na) channel activation and inactivation potassium (K) channel activation ionic reversal (equilibrium) potentials

You should be able to find an answer from the online resources of the module web pages, in any basic neuroscience textbook (there are several in the library) or by searching the world wide web.

Question 2: What does the synapse do?

In your answer, include:

1. How does the postsynaptic signal compare to the presynaptic signal? 2. Describe two types of postsynaptic signal.

Question 3: List the pros and cons of an integrate-and-fire model neuron compared to a compartmental model.

PTO

Exercise: Using the NEURON simulator you will explore the interaction of EPSPs, IPSPs and action potential generation. Download the two files (neuron.hoc and nrnmech.dll) linked to on the module Tutorials web page, saving them in any convenient folder. Use Windows Explorer to navigate to this folder and double-click on neuron.hoc. The following window should appear (ignore the other window containing an error message!):

Click on Help and spend a little time reading the information and trying out the suggestions with the buttons and graph, to get a feel for how NEURON works. DO NOT do the exercises, but instead try out the following.

1. Use the up arrow to increase the IPSP time in increments of 1millisecond. Keep doing this until the IPSP passes over EPSP #1, then #2 and finally #3. What happens when the IPSP overlaps each of the EPSPs, and why?

2. Click Reset and now do the same with EPSP #1, increasing its time until it overlaps with EPSP #2 and #3. Again, what happens and why?

3. Finally, reset and repeat the exercise with EPSP #2, explaining what happens as it approaches, then overlaps EPSP #3 (this is a little tricky!).

Dr Bruce Graham ( b.graham@cs.stir.ac.uk ) Department of Computing Science and Mathematics University of Stirling, Stirling FK9 4LA SCOTLAND