A medical student on their pediatric clerkship arrives to cl…

A medical student on their pediatric clerkship arrives to clinic. Their first patient of the day is an exasperated mother bringing in her 2-year-old daughter for a yearly wellness check. After taking a thorough history, the third-year medical student notices that the child is still wearing pull-up diapers and asks the mother about toilet training. The mother says that she has tried to train her daughter, but that the child repeatedly poops her pants before reaching the bathroom. The third-year medical student recalls the physiological control mechanism of defecation and knows that the child needs to learn to voluntarily control which nerve and muscle?