Structure of the intramural nerves of the rat bladder.

The bladder of adult female rats receives approximately 16,000 axons (i.e., is the target of that many ganglion neurons) of which at least half are sensory. In nerves containing between 40 and 1200 axons cross-sectional area is proportional to number of axons; >99% of axons are unmyelinated. A capsule forms a seal around nerves and ends abruptly where nerves, after branching, contain approximately 10 axons. A single blood vessel is present in many of the large nerves but never in nerves of <600 axons. The number of glial cells was estimated through the number of their nuclei. There is a glial nucleus profile every 76 axonal profiles. Each glial cell is associated with many axons and collectively covers approximately 1, 000 microm of axonal length. In all nerves a few axonal profiles contain large clusters of vesicles independent of microtubules. The axons do not branch; they alter their relative position along the nerve; they vary in size along their length; none has a circular profile. All the axons are fully wrapped by glial cells and never contact each other. The volume of axons is larger than that of glial cells (55%-45%), while the surface of glial cell is twice as extensive as that of axons; there are approximately 2.27 m(2) of axolemma and approximately 4.60 m(2) of glial cell membrane per gram of nerve. Of the mitochondria of a nerve approximately 3/4 are in axons and approximately 1/4 in glial cells.