DEFECATION

 

The ascending and descending pathways and centers are similar to the ones used for micturition. The sympathetic system is inhibitory over the descending colon and rectum, and excitatory over the internal anal sphincter. The parasympathetic system is responsible for the excitatory activity of the rectum and inhibitory of the internal anal sphincter.

 

The afferent and efferent neurons from and to the rectum connect with brain stem centers and cerebral cortex through the spinoreticular and reticulospinal tracts. However these pathways are complex and it has been suggested that other tracts included in the lateral and dorsal funculi may be involved.