NEURAL CONTROL OF SWALLOWING

ABSTRACT BACKGROUND: Swallowing is a motor process with several discordances and a very difficult neurophysiological study. Maybe that is the reason for the scarcity of papers about it. OBJECTIVE: It is to describe the chewing neural control and oral bolus qualification. A review the cranial nerves involved with swallowing and their relationship with the brainstem, cerebellum, base nuclei and cortex was made. METHODS: From the reviewed literature including personal researches and new observations, a consistent and necessary revision of concepts was made, not rarely conflicting. RESULTS AND CONCLUSION: Five different possibilities of the swallowing oral phase are described: nutritional voluntary, primary cortical, semiautomatic, subsequent gulps, and spontaneous. In relation to the neural control of the swallowing pharyngeal phase, the stimulus that triggers the pharyngeal phase is not the pharyngeal contact produced by the bolus passage, but the pharyngeal pressure distension, with or without contents. In nutritional swallowing, food and pressure are transferred, but in the primary cortical oral phase, only pressure is transferred, and the pharyngeal response is similar. The pharyngeal phase incorporates, as its functional part, the oral phase dynamics already in course. The pharyngeal phase starts by action of the pharyngeal plexus, composed of the glossopharyngeal (IX), vagus (X) and accessory (XI) nerves, with involvement of the trigeminal (V), facial (VII), glossopharyngeal (IX) and the hypoglossal (XII) nerves. The cervical plexus (C1, C2) and the hypoglossal nerve on each side form the ansa cervicalis, from where a pathway of cervical origin goes to the geniohyoid muscle, which acts in the elevation of the hyoid-laryngeal complex. We also appraise the neural control of the swallowing esophageal phase. Besides other hypotheses, we consider that it is possible that the longitudinal and circular muscular layers of the esophagus display, respectively, long-pitch and short-pitch spiral fibers. This morphology, associated with the concept of energy preservation, allows us to admit that the contraction of the longitudinal layer, by having a long-pitch spiral arrangement, would be able to widen the esophagus, diminishing the resistance to the flow, probably also by opening of the gastroesophageal transition. In this way, the circular layer, with its short-pitch spiral fibers, would propel the food downwards by sequential contraction.

Some Unresolved Problems concerning the Cochlear Nerve

Three types of afferent fibers innervate the hair cells of the organ of Corti: 1) specific radial fibers which establish contacts with a very few neighboring internal hair cells; 2) spiral fibers, each one of which establishes contact with a number of external hair cells distributed throughout long segments of the cochlea; and 3) unspecific radial fibers which are collaterals arising radially at irregular intervals from fibers of the ganglionic spiral bundles and which establish contact with internal hair cells. The existence of spiral ganglionic bundles of fibers oriented apicalward has long been described, and the fact that a number of ganglionic spiral fibers give off radial collaterals to innervate internal hair cells was illustrated by Cajal and by Lorente de Nó. However, those structural details are not mentioned in the modern literature. In the ventral nucleus there are neurons with efferent axons which join the trapezoid body and cells with short axons ramified within the ventral nucleus itself. Two types of cells with efferent axons are illustrated and described, the spherical or bushy cell and the basket cell; and it is shown that branches of division of the two types of efferent axons form association tracts which end in the tuberculum acusticum. Also, the fact is illustrated that fibers having their cells of origin in that tuberculum form association paths which end in the ventral nucleus by means of extensive ramifications which form numerous synaptic endings. The dendritic and fibrillar plexuses in the ventral nucleus are described, an analysis is made of the relationships between the two plexuses and of the synaptic junctions that mediate transmission of nerve impulses. The synaptic junctions belong to a considerable number of types and in all illustrations the important fact repeatedly appears that one and the same fiber may form synaptic endings of widely different sizes and shapes located either on the same neuron or, more frequently, on different neurons. The intimate structure of each type of synaptic ending cannot be revealed by light microscopy, but only light microscopy can reveal to which kind of fiber the synaptic endings do belong. The presentation is concluded with a brief and preliminary discussion of physiological corollaries of certain general features of the anatomy of the acoustic system.

Endings of the vagus nerve fibers in the mammalian heart

In 1893, Prof. V.V. Nikolaev, having cut vagus nerves of a frog, saw under a microscope degeneration of so-called spiral fibers and pericellular apparatuses on nerve cells of intracardiac nodes. Later these observations were thoroughly verified by Prof. D.V. Polumordvinov and fully confirmed by him. I had a chance to look through amazing by technique preparations of the late Prof. Polumordvinov, obtained by methylene blue method, on which decay of pericellular apparatuses in cardiac ganglia of a frog was absolutely clearly visible. D. V-ch, who died untimely in 1919, unfortunately, did not have time to publish in detail his important study; the manuscript and drawings of his work also remained undiscovered.