Chapter 18 The responses of chemoreceptors with medullated and non-medullated fibres to chemical substances and the mechanical hypothesis

Abstract

This chapter discusses the responses of chemoreceptors with medullated and non-medullated fibres to chemical substances and the mechanical hypothesis. The aortic chemoreceptors were chosen as the test object because this group of sensory receptors not only had both medullated and non-medullated fibres but the receptors of both types of fibres responded in an identical manner to the same natural stimulus—that is, hypoxia. The results showed that for a given dose of acetylcholine (ACh) or phenyldiguanide the aortic chemoreceptors with medullated fibres were either unaffected or if they were stimulated the resulting responses were much smaller than those yielded by endings with non-medullated fibres. Thus there is a striking difference between the conduction velocities of the medullated fibres of aortic and carotid chemoreceptors. This difference could be, as suggested by Fidone and Sato, because of dissimilarity between the aortic and carotid chemoreceptors or it could be because of a difference in the method of measuring conduction velocities of nerve fibres.