Chapter 6 Assessing the Strengths of Motoneuron Inputs: Different Anatomical and Physiological Approaches Compared

Abstract

Publisher Summary The spinal motoneuron is known to be the site of much convergence, in terms of both the total number of axons synapsing on any one neuron and the variety of different sources for these axons. The descriptions of inputs are arrived at piecemeal by a variety of methods. The input neurons of interest in this chapter are the expiratory bulbospinal neurons (EBSNs) of the caudal ventral respiratory group in the medulla of the cat that are located in the nucleus retroambiguus (NRA). The output neurons are thoracic expiratory motoneurons, which innervate internal intercostal and abdominal muscles. The connections from the EBSNs to the expiratory motoneurons may be monosynaptic or polysynaptic. The chapter is concerned with the monosynaptic component, the estimated strength of which has varied widely in different studies. The chapter reviews the published evidence concerning this connection and adds new data from the work in progress. This illustrates the different approaches that have been used to assess the strength of the connection and identify some of the reasons different answers can be obtained. The problems of different interpretations in the chapter are likely to be common to similar studies in other systems of descending fibers, such that the conclusions have some general validity.