[Modality of the bush-like receptors]

In an isolated preparation of the Rana temporaria urinary bladder after a simultaneous morphological and physiological investigation a, structural-functional differentiation of free bushy receptors has been demonstrated. According to arborization character and to the appearance of deferent fibers, the receptors are divided into two types. The first type receptors have a simple structure, a long deferent poorly branching myelin fiber, terminating in a diffuse bush near blood vessels. The second type receptors are of a more complex structure. Their myelin fibers, when leaving the fasciculus, are 4-8 times shorter than the first type receptors, undergo dichotomic and trichotomic divisions several times, and in their distal part they form two initial myelin segments. Their receptory apparatus has a tree-like bush-shaped form and consists of several compact bushes. The impulse activity of the receptors is also characterized by two types of action potentials, differing in their amplitude. When responding to a mechanical stimulation, the high voltage impulse frequency changes, when sodium chloride concentration is increased, the low voltage impulse frequency changes. There is a certain localization of the zones in the preparation from which it is possible to obtain predominantly either low voltage or high voltage responses. The response to the low voltage reaction proves to be obtained from the first type receptors, and that to the high voltage reaction--from the second type receptors. Thus, in the frog, that is on a low phylogenetic stage, differentiation of the free bushy sensitive terminal into mechano- and chemoreceptors is already outlined.