Why do neurotransmitters have to be removed from the receptors?
Neurotransmitter is released from nerve ending when something has to be excited or stimulated , but when the job is done the neurotransmitter has to be removed, otherwise the receptor will be in continuous state of excitation which can be harmful.
example - During muscle contraction , acetylcholine is released at neuromuscular junction which stimulate the muscle cells for contraction. Even after contraction if acetylcholine is present , muscle cell will be in prolonged state of contraction which will cause tetany.
If this thing happens with respiratory muscle , person cannot breathe and will die.