sympathomimetics "mimic" the sympathetic nervous system and therefore have the anticipated result of increasing heart rate and contractility, dilating bronchioles and pupils, and-pertinent to this chapter-relaxing the bladder wall and thus closing the sphincter, affecting urinary retention. Anticholinergics work by blocking the parasympathetic nervous system response, which causes contraction of the bladder and relaxation of the sphincter. thus since this response is blocked, clinically the effects are similar to the sympathomimetics; hence, both drugs are implicated in urinary retention.