(i) What is reflex arc? (ii) How do muscle cells move?

(i) The pathway taken by nerve impluses in a reflex action is called the reflex arc. They allow rapid response, e.g. pulling of hand on touching a hot object.
(ii) Muscle cells have special proteins that change their shape and arrangement in the cell in response to electrical impulse. This forces the muscle cells to contract and relax, causing their movement.