Shifting the circulatory control paradigm.

The current paradigm regards circulatory control as mediated by discrete cardiovascular receptor stimuli, through an array of relatively independent reflexes, with the arterial baroreflex the centrepiece of this schema. However, it is often difficult to fit the linear control model to the observed responses of the intact organism. Hence the need for a more realistic approach. A given disturbance acting on the body stimulates not only baroreceptors, but many other receptors, as well as providing the central nervous system (CNS) with behavioral cues, etc. The mix of stimuli is characteristic of the type and severity of the particular disturbance. The first task for the CNS, is recognition of the pattern of stimuli, which is often a non-linear process. This is mediated through a number of "integrative" centres in different parts of the brain, which compare the magnitude of stimuli from the various sources. The sum of excitatory and inhibitory influences in the efferents from these integrative centres project to "command" centres, e.g. in hypothalamus, amygdala or hindbrain. These generate the output patterns through activation of particular pools of autonomic motoneurons and by altering secretion of hormones. Both the recognition of afferent stimuli (including behaviour) and of the effector patterns, involve mechanisms above and below the pons.