Membrane electrical properties of external urethral and external anal sphincter somatic motoneurons in the decerebrate cat.

Membrane electrical properties of motoneurons innervating the striated muscle of the external urethral and anal sphincters were examined in the decerebrate cat. Both populations of motoneurons had similar electrical properties (mean pooled values; conduction velocity 48 m/s, membrane time constant 3.3 ms, afterhyperpolarization (AHP) duration 97 ms, membrane input resistance 2.2 M omega, rheobase 3.3 nA, and threshold voltage 8.1 mV). Although a portion of cells in both subpopulations of sphincter motoneurons displayed subthreshold conductances (i.e. sag, anomalous rectification), the incidence was higher in the external urethral sphincter motoneurons. The sphincter motoneuron membrane properties were likened to 'slow' hindlimb motoneurons and the low rheobase values suggest that the sphincter motoneurons are easily recruited.