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Unformatted text preview: = r m c m What you will learn in these lectures 1. You will learn that passive electrical properties are important for neural integration over time and space. 2. You will once again see the importance of the chemical and electrical forces. It is these forces that lead to sodium influx after Duckman steps on a pebble. 3. You will learn that current injected into a neuron will cause a voltage change across the cell membrane having a characteristic voltage vs. time waveform. 4. You will learn that the resistive and capacitive properties of the cell membrane give rise to this waveform. 5. You will learn that current injected into a neuron will cause voltage changes across the cell membrane at distant locations. However, these voltage changes will be weaker or attenuated as a function of distance. 6. You will learn that the internal resistance and the membrane resistance are properties that determine how much the voltage across the cell membrane attenuates as a function of distance. 7. You will be introduced to mathematical equations used to predict how the voltage across the cell membrane changes following current injection. Passive Electrical Properties Lectures V = V ss [1-e-(t/ ) ]*[e-(x/ ) ] = (r m /r i ) 1/2 ) ) 1 ( ln( * / on t off e Vss V t = II.A. Duckman puts his foot down and steps on a pebble II.A.1. Neural integration over space and time II.A.2. Summary of neural events occurring when Duckman steps on a pebble II.A.2.a. Sodium enters free nerve ending through stretch receptors II.A.2.b. Near the sodium influx, the voltage of the cell changes II.A.2.c. Na + entering through the free nerve ending is like injecting current into the free nerve ending with an electrode. II.A.2.d. In the rest of these lectures, we will see how sodium flow near the free nerve endings leads to the traveling of an electrical signal over space and time in the neuron. We will do this by inspecting what happens when we inject current into the free nerve ending with an electrode. II.B. How does voltage change in the neuron over time? II.B.1. What does the voltage change over time look like for a step injection of current? II.B.2 What causes the shape of the voltage vs. time graph? II.B.2.a. Membrane capacitance created by the phospholipid bilayer II.B.2.b. Membrane resistance determined by the number of ion channels II.B.3. How do we model and calculate the voltage change over time for an injected step current at the injection point. II.B.3.a. The RC circuit model of the cell membrane II.B.3.b. The time constant equation. II.B.3.c. Properties of the time constant, . II.C. How does voltage change in a neuron as we get further away from the injection point (or further from where Na+ flows through the stretch receptors)?...
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- Fall '08