How do professional leaders assume responsibility?

It depends. Assuming responsibility is adopting the power to address issues. There are 5 sources of power which are

1. Charisma - Professional leaders rarely operate on charisma and it often has little to with resposibility - just ask anyone who studies the history of the Third Reich!

2. Reward - in essence if you do something I'll give you something nice in return.

3. Coercion - the opposite of reward, you do something or I'll make something bad happen to you.

4. Expert - greater knowledge allows you to have your Word accepted as the right thing to do.

5. Position - being a particular role makes you the conduit of information which you can restrict or edit to suit your own purposes. Professional leaders have position power given to them and usually have some element of the others with the exception of charisma. Each of these is used in varying amounts to suit the circumstances.