EXPERIMENTAL STUDIES ON THE AFFERENT INNERVATION OF THE URINARY BLADDER

REPORT II. STUDIES ON THE NEUROGENIC BLADDER

Abstract

Experiments were performed to clarify the mechanism of afferent innervation of the urinary bladder. The afferent impulses from the vesical nerve produced by mechanical stimulation of the bladder were recorded by means of an oscilloscope with continuous photography of the oscilloscopic images. All experiments were performed by using the vesical nerve (N. vesicalis, a branch of N. ischiadicus)-bladder preparations and single afferent myelinated nerve fiber (dissected from the vesical nerve)-bladder preparations of toads (Bufo vulgaris japonicus). In addition electron-microscopic study was carried out to examine the distribution of the diameter of the vesical nerve fibers. These experiments led to the following conclusions.
1) Expansile and contractile autonomic movements of the urinary bladder are smooth and regular. The increase of spontaneous afferent impulses can be seen to occur simultaneously with each bladder contraction.
2) One side of the vesical nerve innervates also the other side of the urinary bladder wall.
3) Any single portion of the bladder wall is innervated by several afferent nerve fibers in an over-lapped manner.
4) Any single afferent nerve fiber innervates only a certain limited area of the bladder wall.
5) The mechanism of producing tension of the detrusor muscle is similar to that of the myotatic reflex or tonic muscle stretch reflex of skeletal muscles.
6) At least three or more types of nerve endings could be distinguished. The first group comprises endings which are stimulated by intravesical pressure. The discharges show a very slow adaptation and usually fade away in 2 to 3 hours or slightly more. About 10 per cent of the nerve endings examined behaved in this manner. The second group comprises endings which are stimulated by the stretch stimuli of the detrusor muscle, and the adaptation to the stimuli was slow or moderately slow. The amplitude of discharge is relatively large. About 75 per cent of the endings examined behaved in this manner. Others, the third type, adapt rapidly and are stimulated by rapid changes in conditions of the bladder wall, e. g., the flexion of the bladder wall. These probably bear no relation to micturition.
7) About 250 nerve fibers are contained within the vesical nerve trunk of the toad. Myelinated nerve fibers occupied about 40 per cent of these, and the rest of them were unmyelinated fibers. In regards to the distribution of the diameters of 128 myelinated and 61 unmyelinated fibers a statistical analysis was made. Myelinated fibers very in diameter ranging from 5.2μ to 0.42μ and unmyelinated fibers, from 3.76μ to 0.27μ. These views were based on the electron microphotographs of the vesical nerve trunk.