## Figure P14

a. When the action potential reaches its peak (positive) value, it is known that gL = 0.3 mS/cm2, gK = 13 mS/cm2, and gNa = 32 mS/cm2. Calculate the membrane time constant for this condition.

b. Assume CM = 0. Calculate Vm at the peak of the action potential.

1.5. Use the HH spike generation model with parameters given in program Hodhux.t in Section 1.4.1 to examine its steady-state current-to-frequency generation properties. Figures 1.4-8 to 1.4-11 in the text were made with Cm = 0.003 mF. See how different Cm values affect the values for A, B, and y in the equation model, f = A + B |jin|Y, for steady-state spike frequency. Also, determine how different Cm values affect the minimum —Jin required to cause periodic spikes. Try Cm = 0.0005, 0.001, 0.005, and 0.01 mF. Use the other parameters given in Hodhux.t

1.6. Use the voltage clamp program HHVCLAMP.T to investigate the effect of a sinusoidal modulation of Vm on spike generation. Use Vs = 70 + Vspk sin(103 2nf t). Vspk is in mV (try different values, e.g., 1, 5, 10, 20 mV). Note that t is in ms, so one needs the 103 factor so f will be in hertz. Vary f over 1 to 100 Hz or so. Plot Vs, Vm, Jin, JNa, JK, JL, and JC.

1.7. This problem investigates a chemical kinetic model for the generation of epsps. Refer to Figure P1.7. At the arrival of a presynaptic nerve spike, the synaptic bouton releases a fraction, ko, of its stored NT, which diffuses across the synaptic cleft to the external surface of the postsynaptic membrane, where it encounters an excess of receptor molecules. One molecule of neurotransmitter combines with one receptor, forming a complex, bNT. Once the NT is bound, the receptor enables an ion channel to open, depolarizing the SSM. The depolarization voltage (epsp) is proportional to the density of bNT. The bound NT is hydrolized by an (excess) enzyme Sub-synaptic membrane

Molecules • Neurotransmitter (NT)

O Inactive NT

Sub-synaptic membrane

Molecules • Neurotransmitter (NT)

O Inactive NT 