EFFECTIVENESS OF ADRENERGIC TRANSMITTER CONCENTRATIONS IN SYNAPTIC CLEFTS OF DIFFERING DIMENSIONS

Publisher Summary This chapter describes the effectiveness of adrenergic transmitter concentrations in synaptic clefts of differing dimensions. The dimensions of the adrenergic neuromuscular synapse show considerable variation in different tissues. In the arterial tree, the synaptic cleft size appears to diminish with vessel diameter. The shortest neuromuscular distance ranges from approximately 20,000 A in the elastic arteries to 1000 A in the smaller arteries, and arterioles. The differing patterns of transmitter distribution and concentration have functional correlates in the contractile responses to nervous activity. In elastic arteries for example, there is no evidence of any special contractile effect, or response resulting from transmitter action on cells closest to the nerve elements. Effector response is the sum total of local transmitter effects on the individual smooth muscle cells in the vessel wall. In muscular arteries, such as the ear artery of the rabbit, there are two phases of response associated with two modes of transmitter excitation.