The chemical control of behavior is a very fragile and fundamental function of the brain. The main systems responsible of it are: the hypothalamus, the Autonomic Nervous system (ANS) and the diffuse modulatory systems.
The hypothalamus is in charge of the maintaining of homeostasis, regulating the function of glands through the liberation of the neurohormones (oxytocin and vasopressin) and the control of pituitary. These systems form a closed loop system when receiving the feedback from other glands in order to maintain the chemical equilibrium. It is very interesting to study the complete loop and to know all the subsystems and processes involved in everyday tasks as the hydration of the body.
The ANS is also a very complicated system that controls several hormonal and visceral processes through its main divisions the sympathetic and parasympathetic systems. These two divisions work together for the functioning of all the autonomous systems. So, in a broad sense, it is also a closed loop system, but this time with two different effector elements. Both divisions work sometimes with the same transmitters, but one of them would generate excitatory activity and the other one inhibitory. The main idea of equilibrium is also present in this case.
Finally, there are the diffuse modulatory systems of the brain, normally called since their main neurotransmitter. The noradrenergic system in locus coeruleus, the serotonergic system in Raphe nuclei, the dopaminergic substantia nigra and ventral tegmental area, and the cholinergic basal forebrain and brain stem are some of the most studied pathways in the brain. All of them related in the control of processes as emotions, learning or memory. Some elements in the functioning of those pathways are of special interest are they could be related to some illnesses as Parkinson’s disease or Alzheimer’s syndrome. But there is also a lot that remains unknown, the use of chemical drugs to study the interaction of those systems is useful but also difficult; when the equilibrium is broken, a cascade of effects is started and the track of those effects is not evident task.
The maintenance of the equilibrium in the body is a very good example of the high complexity of the brain’s work. And it also reveals the fragility of it, if one of the elements in the chemical processes chain is missing or deficient, the consequences could be unexpected and could affect any other element in very different ways. The track of all those interactions will be useful in the treatment of several illnesses and conditions.