Brain
There are dozens of other chemical neurotransmitters that are used in more limited areas of the brain, often areas dedicated to a particular function. Serotonin, for example—the primary target of antidepressant drugs and many dietary aids—comes exclusively from a small brainstem area called the raphe nuclei. Norepinephrine, which is involved in arousal, comes exclusively from a nearby small area called the locus coeruleus. Other neurotransmitters such as acetylcholine and dopamine have multiple sources in the brain, but are not as ubiquitously distributed as glutamate and GABA.
Sam Schmidt Paralysis Foundation
The complexity of the central nervous system makes the formation of the right connections between brain and spinal cord cells very difficult. It is a huge challenge for scientists to recreate the central nervous system as it existed before the injury. Cells called neurons connect with one another to send and receive messages into the brain and spinal cord. Many neurons working together are responsible for every decision made, every emotion or sensation felt, and every action taken. As many as 10,000 different subtypes of neurons have been identified, each specialized to send and receive certain types of information.