Complex sentence: The neurotransmitters sent by the presynaptic cells are the chemical messengers that relay information to the target cells which will be either another neuron of an effector, such as a muscle cell or gland cell.
Split into simpler sentences: The neurotransmitters sent by the presynaptic cells are the chemical messengers that relay information to the target cells. The target cells will be either another neuron or an effector, such as a muscle cell or gland cell.