6. Bd., He/t 4, 1969 P.S. ENGER, J. K. S. JANSEN and L. WALLOE: A Biological Model of Excitation 141 read ( ..... ) ; activate new spindle (1 ........ ) ; <generation of the other spindle processes>; background :-- new backgrproc ; activate background delay equalt; hold (simulationperiod) comment we do not return to this point before the simulation period is completed. In the meantime the spindles are active; end; The SIMULA language has proven its efficiency in a wide range of simulation programs, and the present model compares favourably with comparable models that have been published. As used in the present study a compilation of the program used 8 sec on a UNIVAC 1107 computer. To obtain a de- scription of the behaviour of the model with 15 input spindles over a period of 25 sec, the operation required approximately 110 sec computer time. Re/erences ALN;ES, E., J. K. S. JANSEN, and T. RUI)JORD: Fusimotor ac- tivity in the spinal cat. Acta physiol, scand. 63, 197--212 (1965). 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Thesis, Inst. of Physiol., Oslo University (1968). - - Transmission of information through a second order sensory neuron. In preparation (1969). Dr. LARS WALLOE Institute of Physiology University of Oslo Karl Johans gt. 47 0slo t, Norway A Biological Model of the Excitation of a Second Order Sensory Neurone P. S. E~GER, J. K. S. JANSE~ and L. WALLOE Institute of Physiology, University of Oslo, Norway l~eceived April 25, 1969 Summary. Computer simulation of a relatively simple model can reproduce the main characteristics of the firing patters of some nerve cells. The abdominal stretch receptor of the crayfish has provided an analogous biological model. Synaptic input impulses were simulated by randomly distri- buted, short lasting transmembrane current pulses. Under these experimental conditions the stretch receptor neurone largely behaved as predicted by the computer simulations. Introduction Simulation on digital computers has shown that the behaviour of some nerve cells can be explained by a relatively simple model of the excitation process (STEIN, 1965; WALLOE etal., 1969). An analogous biological model might be of a certain interest. If a