Give a detailed explanation of defecation relex.

Give a detailed explanation of defecation relex.

ANSWER SHOULD INCLUDE:

what does reflex mean?

Firstly; what happens when faeces enter the rectum following 'mass movement '( peristalsis)? I.e. How is stretch of the walls of rectum detected? (Which part of nervous system is involved)? 

Secondly: which sprinter opens? How? ( signal sent via?). What type of muscle is involved? Whis the result? 

Thirsly: How does external sprinters open? ( what type of muscle is it?) . What else aids the expulsion of faeces from anal canal?