Now that you have had fun creating neurons and learning about their different components, it might be helpful to look at how real neural signals might look. ModelDB is a website with hundreds of realistic NEURON models. Here we will show you an example of a pyramidal cell adapted from Kole, 2008, shown below [4]. For detailed instructions on downloading and running NEURON models on your operating system, please visit this page: https://senselab.med.yale.edu/ModelDB/NEURON_DwnldGuide.html
This model allows manipulation of the Na ion channel density on either the dendrite and soma or the axon. Changing the Na channel density changes the conductance of the cell membrane in that segment. Changing the conductance changes the ratio between the change in cell membrane's electrical potential and the amount of current flowing through the membrane. This is dictated by Ohm's law: ΔV = IG
Where ΔV is the change in membrane potential, I is the current flowing through the membrane, and G is the conductance of the membrane.
You can play with this model and discover the different action potential and recording patterns you can create by changing the conductance at the axon and/or at the soma and dendrite. The soma and dendrite are treated as the same segment in this model. Below are three examples of different action potential patterns with their associated recordings and ion channel currents using this model.
Parts a-c are action potentials propagated through the simulated neuron over 12 milliseconds of stimulation. The cells were initiated with a resting potential of -88mV. In part a, the Na conductance at the axon was 3000pS/μm and 50pS/μm at the somatodendritic segment. In part b, the conductance at the axon was increased to 30000pS/μm, leaving the somatodendritic conductance at 50pS/μm and in part c, the axon conductance was returned to 3000pS/μm and the somatodendritic conductance was increased to 500pS/μm. Parts d-f are the transmembrane currents for each of the action potential patterns with the same color scheme as shown above and parts g-i are the recordings obtained from the Backyard Brains recording system. You can see the drastic difference in recording pattern caused by just changing one parameter on the cell! Fantastic! You know how to create your own cell models, how to download and run simulations with realistic neuron models, and how to listen to and record your cells! Now you can explore and discover all of the different ways changing your cells can change the signals you record! Get creative! Play a game with a friend and see if you can communicate with each other through only cell signals. Pretend you're a neurosurgeon; save out a bunch of different cell simulations, have your Matlab code play a random file from those simulations each time it runs and see if you can tell which cell you're recording just by the extracellular recording. Can you make a multicell model and play multiple recordings at the same time? what does that do to your recorded signal? Create your own experiments and upload them here! Interact with your fellow scientists in discussions! Download others' experiments and play with what your peers have created! Scientific collaboration helps everyone understand, learn, and have fun together! We hope you've had a shockingly awesome time with your brains! Check back regularly for new experiments and information from us about your brain, your body, and the nervous system! Kole MH, Ilschner SU, Kampa BM, Williams SR, Ruben PC, Stuart GJ, 2008. Action potential generation requires a high sodium channel density in the axon initial segment. Nat Neurosci, 11, 178-86
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