When jacob saw shadows of people behind him on the walls of the dark alley, his blood pressure increased and breathing rate sped up. these physical reactions were most directly regulated by his: ?

The answer is amygdala. This is the region of the brain that is responsible for emotional responses such as fear and anxiety. It is part of the limbic system and hence important in decision-making. It processes information and sends signals to the hypothalamus and other regions such as the locus coeruleus (that processes fear and panic as in this case).

after a the power stroke, adp is released, but the cross-bridge formed is still in place. atp then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added