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Unformatted text preview: Cellular Neurobiology / BIPN 140 Name__ _______KEY______________ FIRST MIDTERM EXAMINATION Fall, 2007 GENERAL INSTRUCTIONS 1. Please write your name on ALL 7 pages. 2. Please answer each question IN THE SPACE ALLOTTED. 3. For full credit, state your assumptions and show your calculations. 1) _______/10 pts Diane 2) _______/10 pts Diane 3) _______/10 pts Cory 4) _______/20 pts Nicole 5) _______/15 pts Cory 6) _______/10 pts Peter 7) _______/10 pts Peter 8) _______/15 pts Yuri 9) _______/10 pts EXTRA CREDIT Yuri TOTAL ___________/100 pts WAIVER : By signing this waiver I give permission for this exam to be left for me to pick up in the vestibule by the elevator on the 3rd floor of Pacific Hall. I understand that I may only pick up my own exam. I realize that the Department of Biology and its staff cannot take responsibility for exams, which may be stolen or lost, from this area. If I choose not to sign this waiver, I acknowledge that my exam will only be available for pickup 1:30-2:30 p.m., Monday- Friday from 3140 Pacific Hall. ____________________________________ ______________________________ 1. You inject current into a squid giant axon in the presence of TTX and TEA and observe the voltage change as a function of time due to the passive properties of the axon. With some delay, the voltage 1 Cellular Neurobiology / BIPN 140 Name__ _______KEY______________ changes from V rest of 65 mV to a peak at 0 mV. The voltage then starts to decay. After 3 more milliseconds, the voltage has decayed to 35 mV. a. Based on this observation, what is the time constant, tau, for this axon? 5 pts Vt = VinfmV, which is 30 mV above rest. Vinf is 65 mV above rest. 2 pts +30mV = +65mV * e^ (-3/tau) 2 pts tau = -3 / (ln(30/65)) = 3.88 msec 1 pt b. If the membrane resistance, Rm, is 1000 Ohm-cm^2, what is the capacitance, Cm, of the axon? 5 pts tau = Rm*Cm, so Cm = tau/Rm 2 pts Cm = 0.00388 sec / 1000 Ohm-cm^2 2 pts = 3.88*10^-6 sec/Ohm-cm^2 = 3.88 microF/ cm^2 1 pt 2. You are performing voltage clamp experiments on a squid giant axon with standard sodium and potassium channels. In the first experiment, you apply TTX to your bath saline. You then step the voltage from 75 mV to 0 mV and hold it at 0 mV. a. Draw the voltage versus time plot for this experiment. 2 pts Should show a square voltage step from 75 mV to 0 mV and stays at 0 mV. b. If you assume that maximum conductance for potassium 3.33 mS, the activation parameter n for potassium conductance is 0.9, and that the resting potential for potassium is 75 mV, what is the maximum current induced by your voltage step? (Hint: use the Hodgkin-Huxley equation). 6 pts I = C dV/dt + GKmax*n^4*(Vm-EK) + GNamax*m^3*h*(Vm-ENa) + Gleak*(Vm-Eleak) 2 pts At steady state at 0mV, dV/dt = 0, and Vm-Eleak = 0. 2 pts Here, the contribution of Na to the H-H equation is also 0 because of the TTX....
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