ABSTRACT
Implicit in the title of this chapter are two important questions. First, what is the nature of the afferent information relayed centrally in the vagus nerve? This question takes on added significance when one considers that the vagus is predominantly an afferent nerve. The second question concerns the transduction mechanism in mechanoreceptor and chemoreceptor endings. However, a small number of mechanoreceptors have been identified in the serous membrane of the lower esophageal sphincter. The in-series concept was developed in skeletal muscle to distinguish between the "in-parallel" muscle spindle and tendon organ. Under normal circumstances the events signaled by vagal mechano- and chemoreceptors continue without any conscious awareness. Despite the lack of any direct studies of impulse generation in vagal afferent endings, it is probably safe to assume that mechanosensitivity arises following deformation of the receptor ending and the generation of a receptor potential. The study of transduction in gustatory afferents is considerably more developed than that in the gastrointestinal tract.
