Early and late components in the human anal reflex.

Perianal electrical stimulation induces reflex activity in the superficial part of the external anal sphincter muscle. Several components of differing latency can be recognised. It is suggested that these correspond with the ripples of contraction observed clinically after perianal scratch stimuli. Some of our earlier studies suggested an erroneously short latency for the first component of this cutaneously-elicited reflex. The reasons for this are discussed.