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BME 6938 Neurodynamics

BME 6938 Neurodynamics. Instructor: Dr Sachin S Talathi. The cell membrane-equivalent circuit. Pore Resistance. The bilipid layer: Capacitance. The First ODE-For XPPAuto. Passive Membrane with time dependent input current

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BME 6938 Neurodynamics

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  1. BME 6938Neurodynamics Instructor: Dr Sachin S Talathi

  2. The cell membrane-equivalent circuit Pore Resistance The bilipid layer: Capacitance

  3. The First ODE-For XPPAuto • Passive Membrane with time dependent input current • Look up nice tutorial on using xppauto on bards webpage at http://www.math.pitt.edu/~bard/bardware/tut/start.html

  4. XPPAuto ODE File # passive membrane with step function #current: passive.ode parameter R_M=10000, C_m=1, I_0=2, E=-70 parameter t_on=5, t_off=10,Vm=0 dV/dt = (1000*(Vm-V)/R_M + I_0*f(t))/C_M V(0)=0 # define a pulse function f(t)=heav(t_off-t)*heav(t-t_on) # track the current aux ibar=f(t)*I_0 done Comment Define Parameters The ODE Initial Conditions The Function Aux File End of File

  5. The Cable Theory for Passive Cell Use the mathematical frame work of linear cable theory and the elec. circuit representation of neuronal cell membrane to understand how membrane potential is affected in function of neuronal cell geometry. Important to understand concepts like synaptic integration Assumptions: Membrane parameters are linear and independent of mem. potential (passive) ; current entering the cable flows linearly (homogeneous); resistance of extracellular medium is zero (cell immersed in homogeneous isopotential medium, the reference)

  6. Kirchoff’s Current law applied to cable Cm: Membrane Capacitance (F) Rm: Membrane Resistance (Ohm) Ra: Axial Resistance (Ohm) Iext: External current (Amp) Ijext

  7. The Cable Equation CM: Specific Capacitance (F/cm2) RM: Specific Resistance (Ohm-cm2) RA: Specific Axial Resistance (Ohm-cm) iext: Current density (Amp/cm2)

  8. The Cable Equation: Rescaling Variables

  9. Recap The Cable Equation IM IL d IM: Membrane Current (Amp/cm2) CM: Specific Capacitance (F/cm2) RM: Specific Resistance (Ohm-cm2) RA: Specific Axial Resistance (Ohm-cm) Space Constant Time Constant The Cable Equation: Steady State

  10. Longitudinal Current: Input Resistance Im V (x) V (x+Δx) Il(x) RL: Cytoplasmic Resistance per unit length (Ohm/cm)

  11. The Cable Equation: Steady State Green’s Function G(X): Solution to Steady State Cable Equation for with boundary conditions: (Infinite cable) Solution to Steady State Cable Equation:

  12. Steady State: Boundary Conditions Boundary Condition Cable Type Schematic Diagram • Semi-Infinite Cable • Finite Cable Sealed End • (closed circuit) • Finite Cable Open End • (open circuit) • Finite Cable Clamped End

  13. Semi-Infinite Cable: Constant Current I0

  14. Finite Cable: Constant Current Length of Cable: l Dimensionless Length: General Solution: Conductance of terminal end Conductance of semi-infinite cable

  15. Finite Cable: Sealed End I0 L

  16. Finite Cable: Open End I0 L

  17. Finite Cable: Clamped End I0 L

  18. Steady State Solution Boundary Condition Cable Type Solution • Semi-Infinite Cable • Finite Cable Sealed End • Finite Cable Open End • Finite Cable Clamped End

  19. Steady State Solution

  20. Cable Equation: Transient Solution Green’s Function G(X,T) for infinite cable: solution of above equation for: With initial condition: and Boundary condition: General Solution to Cable Equation: Hint: Use the formula:

  21. Ralls Model-Equivalent cylinder • Basic Idea: Impedence matching • Assumptions: • The membrane properties are identical for soma and dendritic • branches. • 2. Membrane properties are uniform and voltage independent • 3. All dendritic branches terminate at the same electrotonic length (and the tip of dendrite ends are sealed) Class assignment: Please read sections 4.5.1.3 and 4.5.2 on your own.

  22. Synaptic Integration Model for current injection into neuron through synapse-alpha function Use XPP AUTO to answer following Questions (Cable.ode) 1. Sketch the potential at the soma for the synaptic input at compartments 0, 5, 10, and 20. 1a.How do the peak amplitudes depend on distance? 1b. How about the time to peak? 1c.Does the peak appear to decay slower or faster for more distant inputs? 1d. How does the potential scale across various compartments For synaptic input at different locations on the cable

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