# Simulation of Spinal Cord Reflexes
## 3 The Electronic Circuitry for the Models of Different Neuron Types
### The Electronic Scheme Model and Signal Diagram for the Recurrent Inhibition Reflex  
The schemes in Figure 14A,B show two models, one with BJT and one with CMOS, for the loopback inhibition, using a Renshaw neuron. We used a pulse signal V2 of 5 V, 50 Hz, and 1 ms duty time, applied to the excitatory Vil synapse input. We collected the output signal and made a negative feedback loop, routing it to the neuron input using a potentiometer with one of its terminals connected to the Vij inhibitory synapse input. Knowing that the Renshaw neuron is used only for negative feedback, we considered it sufficient to simulate it by the feedback potentiometer. We obtained the diagram shown in Figure 15 for poor feedback and the diagram shown in Figure 15 for strong feedback. It can be observed that the output signal frequency significantly decreases when the feedback is stronger. To conduct the simulations, an 1 M\(\Omega\) potentiometer was sufficient for the blocks designed with BJT. For the blocks designed with CMOS, a potentiometer with one order of magnitude greater was necessary. This is the only difference observed between the simulations with BJT and CMOS. Figure 12: Block scheme for the general neuron type with R6 = 100 K and V1 d.c. 3.65 V acting like a sensitive neuron, using BJT (**a**) and CMOS (**b**). Figure 13: Signal diagram for the sensitive neuron model with R6 = 100 K, and V1 = 3.65 V d.c. Figure 17A,B provide the schemes for the spinal reflexes, as they are described in [1]. We took into account the loops for the stretch reflex of the flexor muscle and the extensor muscle acting as a limb segment in one of the limb joints. The loops for the autogenic inhibition reflex, present as the agonist muscle for the flexor muscle, which is inhibited, and for the extension muscle as the antagonist muscle, which is facilitated, were all considered. So too were the loops for the flexion reflex at a noocicptor, present in the flexor muscle as the agonist muscle and in the extension muscle as the antagonist muscle. Every instantaneous sensation generating a reflex was simulated by using voltage-controlled switches with their control voltage established by a potentiometer. Using the directive \"_model\", we established that when the voltage at the potentiometer cursor exceeds 3 V, the switch is turned on obtaining 5 V at the excitation synapse input of the associated sensitive neuron and a 50 Hz pulse signal at its output. Every motor neuron has an associated inhibition neuron acting through an inhibition synapse and an associated excitation neuron acting through an excitation synapse. Input signals are coming from the brain stem BS for both of the inhibitory neurons. Input signals are coming from the motor cortex MC, acting directly on motor neurons by excitation synapses. The pulse signal  
Figure 14: (**A**) General neuron scheme with Renshaw neuron feedback with R6 = 900 K, Vi1 Pulse (5 V, 50 Hz, and 0.001 s duty time), with BJT blocks. (**B**) General neuron scheme with Renshaw neuron feedback with R6 = 900 K, Vi1 Pulse (5 V, 50 Hz, and 0.001 s duty time), with CMOS blocks. frequency from BS and MC is 10 Hz, simulating rest. Taking into account the neuronal signal frequency, the signals coming from BS and MC should not interfere with the pulse signal from the sensitive neuron, which has a much higher frequency value. Figure 16: Scheme diagram for the general neuron with Renshaw neuron feedback with R6 = 900 K and pronounced feedback. Figure 17: _Cont._  
Figure 15: Scheme diagram for the general neuron with Renshaw neuron feedback with R6 = 900 K and poor feedback. The signal diagram for the myotatic reflex present in the flexor muscle and reciprocal inhibition reflex present in the extensor muscle is given in Figure 18 and follows the paths I1-O1-I5-O5 and I1-O1-I9-O9-I6-O6. The signal diagram for the myotatic reflex present in the extensor muscle and reciprocal inhibition reflex present in the flexor muscle is given in Figure 19 and follows the paths I4-O4-I6-O6 and I4-O4-I7-O7-I5-O5.