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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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- Spring '09
- Neurobiology, pts