Motor neurons, also known as efferent neurons, are the connecting unit between the muscular system and the central nervous system. They carry information from the nervous system to the muscles. The signals are transmitted through the neurons to the effector organs where an impulse has to be generated. In case of muscles, these impulses can be relaxation and contraction and in case of glands they can be a signal to secrete hormone. Acetylcholine is a neurotransmitter that passes the impulse from a neuron to a muscle.