Number of fibres and fibre diameter distributions of nerves innervating the urinary bladder in humans. Acceptor nerve analysis. II.(IV).

1. The nerves innervating the urinary bladder were analysed morphometrically for their nerve fibre number and their nerve fibre group composition. 2. The nervi pelvini contained about 4000 myelinated nerve fibres, the nervi rectales inferiores and perineales 1700 and the nervus hypogastricus 2000 fibres. 3. An upper limit for somatic sphincteric alpha 2-motoneurons was 30 in the nervi rectales inferiores and perineales. The nervi pelvini contained about 400 fibres with diameters between 7 and 15 microns and myelin sheath thicknesses between 1.8 and 2.3 microns. Some of these thick nerve fibres could innervate the external urethral sphincter. It is estimated that the number of efferent parasympathetic fibres in the nervi pelvini on one side was about 800, which makes about 20% of all the myelinated fibres of the nervi pelvini. 4. It is discussed that efferent fibres to the external bladder sphincter may lead through the nervi pelvini or a direct branch instead of leading through the pudendal nerve. 5. In the Clinical Implications it is summarized that one intercostal nerve (9000 afferents, 1000 efferents) with its dissectable skin (3000 aff), muscle (300 aff, 300 eff) and mixed branches (2500 aff, 1500 eff) contains enough myelinated fibres for a reinnervation of the detrusor (3200 aff, 800 eff), the external anal and bladder sphincters (30 aff, 30 eff), the mucosa of the urethra, trigonum vesicae and anal canal (200 aff) and the lower sacral skin (6000 aff) on one side if one intends to restorate urinary bladder function in paraplegia by a nerve anastomosis. Reasons for a loss of plasticity of the injured spinal cord are given.