End

Figure 4.1-7 illustrates the uninhibited PSN model response to two nearly coincidental excitatory epsps with different weights. Three output pulses are produced by the SGL. Note that the generator potential of the SGL, v1, is reset each time the RPFM SGL model generates a pulse. Figure 4.1-8 shows that one pulse to the inhibitory synapse at t = 1 ms prevents postsynaptic firing. Model parameters are listed in the program above. The traces are 1 = Ve1, 2 = Ve2, 3 = Hi, 4 = v1, 5 = y1 (SGL output), 6 = Vex.

4.1.6 Discussion

Neural inputs to neurons can be inhibitory as well as excitatory, permitting gating or downward modulation of information flow. An example of such downward modulation by inhibition is seen in the neuronal system carrying pain information to the brain. Potassium-gating inhibitory synapses generate negatively going ipsps which can sum with positively going epsps in passive dendrites and membrane. A dominance of ipsps over epsps will slow or stop the firing of a neuron.

A more powerful form of inhibition is found in the chloride-gating axosomatic synapses that make contact with the PSN near its SGL. Activation of a chloride-gated

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