PHGY 212 Lecture Notes - Threshold Voltage, Chronaxie, Sciatic Nerve
21 Nov 2012
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Document Summary
The cap is the sum of the individual fibre action potentials. As you increase stimulus strength you recruit more fibres, thus generating more action potentials, making the cap look like a larger bell-curve like shape. Since the nerve is composed of many fibres with various diameters, the fast fibres (larger diameters) appear at the head section of the cap, and slow fibres (small diameters) appear at the tail section of the cap. As stimulus strength increases, you get a wider. Measuring the latency for the beginning of the cap shows how long it takes for fast fibres to produce an action potential from the stimulus to the recording electrode. The threshold voltage is the voltage needed to produce at least one ap from a fibre in the sciatic nerve. Since we are dealing with cap thresholds and not individual thresholds, it is hard to measure accurate thresholds. The curve flattens out at the rheobase at around 1ms.
