"Central command" and sympathetic activation

The concepts of "central command" and of peripheral feedback mechanisms are analysed in order to individuate the main regulatory components of sympathetic efferent activity. In recent years a new afferent channel has been described: it consists of cardiovascular sympathetic afferent fibres which play a tonic function in the regulation of the sympathetic outflow. This afferent channel mediates reflexes which are mainly excitatory in nature with positive feedback characteristics. In this way, each particular haemodynamic neurally-regulated state can be hypothesized as under the control of "central command" and of opposite peripheral influences represented by the continuous interaction of negative and positive feedback mechanisms.