Brain stem control of swallowing: Neuronal network and cellular mechanisms

Swallowing movements are produced by a central pattern generator located in the medulla oblongata. It has been Established on the basis of microelectr ode recordings that the swallowing network includes two main groups of neur ons. One group is located within the dorsal medulla and contains the genera tor neurons involved in triggering, shaping, and timing the sequential or r hythmic swallowing pattern. Interestingly, these generator neurons are situ ated within a primary sensory relay, that is, the nucleus tractus solitarii . The second group is located in the ventrolateral medulla and contains swi tching neurons, which distribute the swallowing drive to the various pools of motoneurons involved in swallowing. This review focuses on the brain ste m mechanisms underlying the generation of sequential and rhythmic swallowin g movements. It analyzes the neuronal circuitry, the cellular propel-ties o f neurons, and the neurotransmitters possibly involved, as well as the peri pheral and central inputs which shape the output; of the network appropriat ely so that the swallowing movements correspond to the bolus to be swallowe d. The mechanisms possibly involved in pattern generation and the possible flexibility of the swallowing central pattern generator are discussed.