The neurotransmitters in the brain and spinal cord and their modes of action are not yet fully understood. It is believed however that noradrenaline, gamma aminobutyric acid (GABA) and acetylcholine act as neurotransmitters. Other substances, such as dopamine, serotonin (5-hydroxytryptamine), enkephalins, endorphins and substance P, have similar functions. Somatic nerves carry impulse directly to the synapse at skeletal muscles: the neuromuscular junctions.
In autonomic nerves, impulse travels along two nerves (preganglionic and postganglionic) and across two synapses to the effector organs in both the sympathetic and the parasympathetic division.