Muscle spindles in the human bulbospongiosus and ischiocavernosus muscles.

Introduction: Muscle spindles are crucial for neuronal regulation of striated muscles, but their presence and involvement in the superficial perineal muscles is not known.
Methods: Bulbospongiosus and ischiocavernosus muscle specimens were obtained from 31 human cadavers. Serial sections were stained with hematoxylin and eosin, Sirius red, antibodies against Podocalyxin, myosin heavy chain isoforms (MyHC-slow tonic, S46; MyHC-2a/2x, A4.74), and neurofilament for the purpose of muscle spindle screening, counting, and characterization.
Results: A low but consistent number of spindles were detected in both muscles. The muscles contained few intrafusal fibers, but otherwise showed normal spindle morphology. The extrafusal fibers of both muscles were small in diameter.
Conclusions: The presence of muscle spindles in bulbospongiosus and ischiocavernosus muscles supports physiological models of pelvic floor regulation and may provide a basis for further clinical observations regarding sexual function and micturition. The small number of muscle spindles points to a minor level of proprioceptive regulation.
(© 2014 Wiley Periodicals, Inc.)