During resting state, the muscle cell membrane is in a polarised state and the membrane is negatively charged. When the muscle is stimulated by electrical stimulus, acetylcholine (ACh) is liberated at neuromuscular junction. ACh increases the membrane permeability of Na+ and K+ ions.
The neurotransmitter released at the ganglia and effector organ in parasympathetic nervous system is, acetylcholine. In sympathetic nervous system, the neurons release norepinephrine at the effector organ.
Thus, the blanks can be filled with acetylcholine; acetylcholine; acetylcholine; norepinephrine.