There many different neurotransmitters, each exerting different effects on the brain and body depending on which receptors they activate. Some of the more common include acetylcholine, which has a role in memory and movement; noradrenaline, which is needed to feel awake and alert; serotonin, also known as 5-hydroxytryptamine or 5-HT, which is influential in mood, appetite and pain; histamine, which is integral to the body’s immune response; vasopressin, which controls water levels in the body; and dopamine, which has a large number of roles including in movement, mood, memory and understanding. 

While all neurons have the same structure, there are many different types. In the spinal cord, there are three main neurons: sensory, which are activated by physical or chemical inputs such as sound, heat, light, taste and smell; motor, which transmit impulses to muscles and enable movement; and interneurons, which connect with each other as well as with other neuron types. In the brain, classification of neurons is more complicated, with the motor or sensory grouping sometimes employed, but the type of neurotransmitter used by the neurons is another method of categorisation.