Computer Model for a Controller System of Spinal Reflex Patterns

Nervous system presents the grey and the white matter. The cord grey matter is the integrative area for the spinal reflexes and other motor functions. Sensory signals enter the cord through the sensory nerve roots, and after they have two different destinations: (a) the grey matter of the cord, where some sensory fibre or its collaterals terminate; and (b) nervous system higher levels, reaching in suprasegmental areas. The brain is considered to be the suprasegmental nervous system, while spinal cord and brain stem form segmental nervous system [4,6]. Spinal reflex responses are modulating by hierarchical motor control that is attributed to serial activation of a motor command chain [2], just due to those collateral sensory fibres, which ascend to higher segmental levels and supra-segmental areas. Many of the ascending tracts pass through the reticular formation, and the fibres of reticulospinal tracts terminate on the motor of the anterior horn. Reticular formation is an important area involved in the spinal reflex control, but its action on spinal depends of commands from the higher levels. We adopted a simple neural circuit model to simulate a controller system of spinal reflex patterns. We determined the equations represent the non-linear behaviour of the system components, and adopted boundary conditions were based on several known characteristics of the synaptic transmission. We used a set of oscillators coupled in two dimensions forming a matrix 10X10 to simulate the cortex area related to that motor command chain [3]. So, our model associates the properties of the segmental reflex with the single-unit characteristics common in electrophysiological investigation. It includes the depolarising stimulus from Ia-fiber system, which represents the activity proprioceptive from muscular receptors, and hyperpolarizing stimulus from inhibitory neurones, which are involved in reciprocal inhibition mechanism of the motor control [1,5]. A Fortran for Windows Power Station based program was developed based on the model. Routines were developed to the model elements. Such routines were coupled and numerical values typical of parameters related to the neuron membrane and the interneuronal synapses found in the literature were applied. So, we examined the ability of our model to reproduce the behaviour of a spinal neural circuit generator of reflex pattern by means of frequency spectra generate by the ΜΝ outputs. In conclusion, our spinal reflex model produced the expected response pattern. The used values and compute language became relatively easy to correlate the results to that from experimental studies. Besides, the simulation environment can be easily expanded to include additional neuronal geometry, as well as cell and fiber populations can be added to the model.