Describe your four tracings and explain what has happened in each of them.

I am stuck on just a few questions and wondered if anyone could help me out.

Activity 3 question: An individual muscle fiber follows the all-or-none principle—it will either contract 100% or not at all.  Does the muscle we are working with exhibit the all-or-none principle?  Why or why not?

Activity 9 question:  Describe your four tracings and explain what has happened in each of them.  My first three tracings are flat and the fourth has a slight rise and fall but I am stuck as to why this is happening to each

Thank you in advace for your help