Presentation on theme: "This PowerPoint shows circuit diagrams superimposed on the membrane in order to illustrate current flow in three of the tutorials: The Membrane Tutorial."— Presentation transcript:
1This PowerPoint shows circuit diagrams superimposed on the membrane in order to illustrate current flow in three of the tutorials:The Membrane Tutorial (diagrams of current flow that accompany the steps of the tutorial)The Unmyelinated Axon TutorialThe Myelinated Axon TutorialAnn E. Stuart
2c Patch Membrane Tutorial outside inside Vm = 0 mV stimulating electrode insertedVmoutsideinsidecCurrent may be injected through a microelectrode.
3c Patch Membrane Tutorial outside inside Vm = 0 mV Ach-gated channels Current may also be injected by the opening of a channel.
4Patch Membrane Tutorial steps 1 & 2 Vm = 200 mV at end of current pulseVmelectrode injects positive charge(20nA current pulse)Vminjected current pulse
5Patch Membrane Tutorial steps 1 & 2 Vm = 200 mV at end of current pulseVmelectrode injects positive charge(20nA current pulse)Vminjected current pulse
6Patch Membrane Tutorial steps 1 & 2 Vm = 200 mV at end of pulseVmQ = CVV = 1/C [Q]dV/dT = 1/C [dQ/dt];dQ/dt = IcapdV/dT = 1/C [Icap]Icap = C [dV/dt]
8Time constant tau = Rm Cm tau = the time it takes for voltage to rise to 67% (1-1/e) or fall to 33% (1/e) of its final valueVmtau = Rm CmVmtautaut
9Patch Membrane Tutorial step 4: add HH Na & K channels Na channels (fast)Depolarizing (positive) current is injected.K channels (slow)VmK channels then open, allowing the K battery to drive positive current out through these channels (inward Icap).The current first flows out through the capacitance C.As the voltage builds up across C, current flows out through leak channels.Na channels open, allowing the Na battery to drive positive current inward through these channels (outward Icap).
11Length constant (L)L = the distance over which a voltage step decays to 1/e (33%) of its original value.If rm is large compared to ri, current will flow down the inside of the axon and L will be large.L tracks the (square root of the) rm/ri ratio:L = √ rm / rimVLdistance x
12Unmyelinated Axon Tutorial: add HH Na & K channels the AP
13Myelinated Axon Tutorial: add myelin the APtime constant:tau = RmCmCm decreases because of many capactors in seriesRm increases because of equivalent # of resistors in seriestau does not changelength constant:L = √ rm/rirm becomes very much largerL becomes very much longer