HOME >HOMEWORK #4

Reading (one of the following)
Aidley Chapter 10 p 173-190
or KSJ (4th edition) Chapter 14 p 253-270
or KSJ (3rd edition) Chapter 13

1. The absorption of a photon by a rod causes the voltage to decrease by about 2 mV, from -40 to -42 mV for 0.2 seconds. When the cell is at -40 mV, the average rate of release of synaptic vesicles is 1000 per 200 ms. The rate of release of synaptic vesicles decreases 10-fold for every 15 mV decrease in the cell's voltage (in other words, at -55 mV, 100 vesicles are released per 200 ms, at -70 mV, 10 vesicles are released, etc). Given that the actual number of released vesicles is Poisson distributed, would a 2 mV change in voltage produce a significant change in the rate of vesicle release?

2. Now imagine a cone cell. The absorption of a single photon by a cone produces a voltage change of about 0.02 mV for 0.1 seconds. If everything else is the same as in the rod (i.e. average rate of vesicle release, voltage dependence of vesicle release, etc., see problem #1), would a single photon absorbed by a cone produce a significant change in the rate of vesicle release from the cone?

3. The voltage and current in a bipolar cell is set by the rate of synaptic vesicle release from the photoreceptors. Would you expect the magnitude of noise in the bipolar cell (voltage or current fluctuations) to be larger in complete darkness or bright light? Why?