To clarify the appropriate therapy on the neurogenic bladder, the innervation and the pathological physiology of the urinary bladder received various injuries on its nervous system was studied, and many works presented from our clinic. On the other hand, it is well known that the pudendal nerve had very important role in the mechanism of micturition, while the blocking of this nerve is recognized as one of the available therapy against the neurogenic bladder.
Here, the histological studies on the innervation of the pudendal nerve, especially the dorsal nerve of penis, on the urethra and the penis, and the origin of that nerve in the spinal cord were performed with the observation of degenerated nerve fibers following the section of various spinal nerves, and the results described below were obtained.
1) In the adult male dog, the pudendal nerve occures in the form of one bundle from the pudendal plexus, and this bundle branches away the dorsal nerve of penis. This nerve branches again into the ramus penis and the rami urethrae posterior, the former extends to the top of the penis along the dorsal part of the penis, while the latter spreads to the somewhat upper part of the prostate along the ventral part of the posterior urethra. These facts reveal the innervation of the pudendal nerve to the posterior part of the urethra.
2) The composition of the myelinated nerve fibers in the pudendal nerve and the dorsal nerve of penis was examined in 20 cases adult male dog. The average number of the total myelinated nerve fibers was 3484 in the main trunk of the pudendal nerve, 1556 in the ramus penis of the dorsal nerve of penis, 405 in the proximal part of the rami urethrae posterior, and 172 in the peripheral part of this rami. While, any of these were composed of the small-sized nerve fibers in 71.5-74.5%, medium-sized in 22.2-24.4%, large-sized fibers in 2.4-4.5%, and maximum-sized fibers in 0.6-1.0%, respectively, and it was remarkable that the innervation of the small-sized nerve fibers was significantly dominant comparing to that of other fibers.
3) After the section of main trunk of the pudendal nerve, 88.1-95.5% of the nerve fibers in the ramus penis and 88.1-96.3% of that in the rami urethrae posterior were degenerated, while 0.1-0.3% of the nerve fibers only in the ramus penis were degenerated after the section of the pelvic or the hypogastric nerve. With these results it was assumed that the most part of the penis and the posterior urethra was innervated by the pudendal nerve, and only a part of the ramus penis was contributed by the pelvic and the hypogastric nerves.
4) With the observation on the degenerated fibers, 86.9-88.9% of the nerve fibers in the ramus penis and 47.5-56.7% in the rami urethrae posterior were originated from the dorsal root of the S_1-3 spinal nerves and corresponded to the pudendal nerve or the dorsal nerve of penis; while, 6.8-8.8% in the ramus penis and 23.3-31.7% in the rami urethrae posterior was originated from the ventral root of the same spinal nerves, respectively. Therefore, it was clarified that the innervation of S_1-3 dorsal root was dominant in the pudendal nerve and the dorsal nerve of penis, especially in the ramus penis; while the innervation of S_1-3 ventral root was significant in the rami urethrae posterior and poor in the ramus penis. And furthermore, the most significant correspondence of innervation of the spinal nerve against the pudendal nerve or the dorsal nerve of penis was found in the 2nd sacral nerve concerning to both the ventral and the dorsal root nerve fibers, and this was followed by the 1st and then 3rd sacral nerves.
5) The centrifugal nerve fibers of the dorsal root in the pudendal nerve and the dorsal nerve of penis was examined by the section of the dorsal root of the spinal nerve, and the degenerated nerve fibers in 4.8-8.2% of the myelinated fibers of these nerves. This results show the existence of the centrifu