title: Morphological analysis of the external anal sphincter motor nerve and its motoneurons in the cat.
abstract: To investigate the spinal neural circuitry that controls the tonus of the external anal sphincter (EAS) in the cat, the size distribution of EAS motor fibers and their motoneurons (MN) was examined, and the presence of muscle spindles in EAS musculature was also tested for. The size distribution of EAS motor fibers was examined after degeneration of afferent fibers and that of their MN was measured, after labeling the cells with horseradish peroxidase. Both distributions were unimodal, thereby demonstrating the difficulty of distinguishing between alpha and potential gamma MN; but muscle spindles were not found in the musculature. Mechanisms underlying the spinally controlled tonus of the EAS remain unclear, including the nature and role of spinal reflexes. It is argued that non-spindle sensory receptors in the anal canal may provide the sensory component of a reflex circuit that contributes to this tonus.
authors.affiliation: Anatomy and Physiological Science, Department of Life Sciences and Bio-informatics, Tokyo Medical and Dental University, Tokyo, Japan. k.muramatsu.aps@tmd.ac.jp
authors.forename: Ken
authors.initials: K
authors.lastname: Muramatsu
authors.forename: Sei-Ichi
authors.initials: S
authors.lastname: Sasaki
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Cho
authors.forename: Kenji
authors.initials: K
authors.lastname: Sato
mesh_terms: D001003:Anal Canal / Q000033:anatomy & histology* / Q000294:innervation*; D000818:Animals; D002415:Cats / Q000033:anatomy & histology*; D005260:Female; D008297:Male; D009046:Motor Neurons / Q000166:cytology*; D009412:Nerve Fibers / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000166:cytology; D010525:Peripheral Nerves / Q000166:cytology