中枢神経障害とえん下 えん下の中枢制御機構

Abstract

Sensory information from the pharynx and larynx are essential to induce the sequence of protective reflexes of the upper airway, such as swallowing and coughing. The sensations received by the pharyngeal and laryngeal mucous are transmitted to the nucleus tractus solitarius (NTS) via the glossopharyngeal nerve (GPN) and the superior laryngeal nerve (SLN) .The motor pattern for pharyngeal swallowing is quite stereotyped. Once swallowing has been initiated, no additional peripheral afferents are needed for its completion. This suggests that swallowing is produced by a central pattern generator (CPG), which is likely to be located in the medulla oblongata. The CPG is activated when the number of sensory impulses exceeds a certain threshold, which is modulated by the cortex through the corticobulbar tract.Swallowing-related neurons (SRNs) were recorded systematically in the medulla oblongata of anesthetized cats. These SRNs received orthodromic inputs from the superior laryngeal nerve (SLN) and showed transient changes in their activity synchronous with swallowing. These neurons could be divided into three types : Type I SRNs are sensory-relay neurons from the SLN in the NTS ; Type II are interneurons located diffusely in the parvocellular reticular formation ventral to the NTS, which received oligosynaptic inputs from the SLN ; and Type III are motoneurons in the nucleus ambiguus. Some Type II neurons still showed a swallowing activity even after the animals were paralyzed, which suggests that they could be involved in the generation of swallowing outputs.The threshold for triggering the CPG is influenced by output from the cerebral cortex. The region of the cortex related to swallowing is located in the rostral part of the orbital gyrus and sends output to the SRNs. This pathway modulates the threshold for the activation of the CPG and regulates excitability in the elicitation of swallowing.