Lecture 3: linearizing the HH equations HH system is 4-d, nonlinear. For some insight, linearize around a (subthreshold) resting state. (Can vary resting voltage V 0 by varying constant injected current I 0.) Ref: C Koch, Biophysics of Computation, Ch 10
Full Hodgkin-Huxley model
4 coupled nonlinear differential equations
Spikes, threshold, subthreshold dynamics threshold propertyspike
Spikes, threshold, subthreshold dynamics threshold propertyspike sub- and suprathreshold regions
Linearizing the current equation: Equilibrium: V 0, I 0
Linearizing the current equation: Equilibrium: V 0, I 0 Small perturbations:
Linearizing the current equation: Equilibrium: V 0, I 0 Small perturbations:
Linearizing the current equation: Equilibrium: V 0, I 0 Small perturbations:
Linearizing the current equation: Equilibrium: V 0, I 0 Small perturbations:
Linearized equations for gating variables fromwith
Linearized equations for gating variables fromwith
Linearized equations for gating variables fromwith
Linearized equations for gating variables fromwith Harmonic time dependence:
Linearized equations for gating variables fromwith Harmonic time dependence:
Linearized equations for gating variables fromwith Harmonic time dependence: solution:
Linearized equations for gating variables fromwith Harmonic time dependence: solution: or
So back in current equation
For sigmoidal
So back in current equation For sigmoidal
So back in current equation For sigmoidal
So back in current equation For sigmoidal like a current
So back in current equation For sigmoidal like a current i.e.
So back in current equation For sigmoidal like a current i.e. or
So back in current equation For sigmoidal like a current i.e. or equation for an RL series circuit with
Equivalent circuit component
Full linearized equation:
A( )= 1/R( ) = admittance
Full linearized equation: A( )= 1/R( ) = admittance Equivalent circuit for Na terms:
Impedance( ) for HH squid neuron ( =2 f )
Impedance( ) for HH squid neuron experiment: ( =2 f )
Impedance( ) for HH squid neuron experiment: ( =2 f ) Band-pass filtering (like underdamped harmonic oscillator)
Cortical pyramidal cell (model) (log scale)
Damped oscillations Responses to different current steps: