Different areas of gray matter are specialized in different functions, such as moving, seeing, touching, listening, thinking, or modulating physical functions. These specialized areas of gray matter are connected to one another through fibers that are like wires; these fiber tracks are the material that we see in the brain as white matter.

When communication between the centers in the brain breaks down, it may be due either to direct damage to a center of gray matter or to damage to the wiring between the centers. The brain has an amazing adaptive capacity that is sometimes referred to as "plasticity" - when damage occurs, messages can be sent through alternate connections.

It should be of greatest interest to psychiatry. Many brain scientists believe that the key to understanding many aspects of mental illness may lie within the limbic system and its connections. This may be the part of the brain that has been somehow "broken" in at least some of these patients suffering from the schizophrenias or the affective disorders. No specific defects in the limbic system has been uncovered as yet, but a clustering of evidence from the study of brain chemistry and the effects of drugs contains many tantalizing hints.

Patients with affective disorder, particularly some types of depression, may be suffering from an imbalance in the hypothalamic-pituitary-adrenal axis. Many of the symptoms of affective disorder are consistent with these types of neroendocrine abnormality, since they involve changes in appetite, sleep regulation, and adaptability to stress and change.

Organization of the brain at cellular level

The building blocks of the brain are nerve cells of two types: neurones (10%) and glial cells (90%). At the moment, most neuroscientists think the neurones do most of the work of the brain by formulating and transmitting all the messages that it carries. The glial cells are thought to be cementing, supporting, and nourishing structures for the neurones. Some other function may be discovered for the glial cells.

Neurones differ in shape and appearance, depending on their purpose. Some are specialised to receive messages - the afferent( running in) neurones or bipolar neurones. Others are specialised to send out messages - the efferent (running out) neurones. There are also many neurones which provide connections between afferents and efferents. These types of cells are called "interneurons".

The main work center of the neuron is the cell body, which contains the nucleus of the cell. The cell bodies send out tiny fingers of branching fibers called "dendrites". This tree like web around the cell body enormously increases its ability to receive information. In addition to the dendrites, the cell body sends out a long tubular projection (the axon) that it uses to communicate with other neurones. The axons are the "wires" of the nervous system, and constitute the white matter of the brain. Different parts of the cortex contain different kinds of neurones arranged in somewhat different patterns.

Communications between neurones

The messages are sent down the axons through a process of electrical conduction. It is filled with a fluid containing a high concentration of ions such as sodium, potassium, and chloride. When the electrical impulse flowing down the axon reaches its end, it spreads out in hundreds of nerve terminals that communicate with the dendrites and cell bodies of many other neurones.

The communication point between neurones is referred to as the "synapse". The negative electrical current is passing down the axon by hopping from node to node, eventually bringing a positive charge to the nerve terminal. At the end of nerve terminal there are hundreds of tiny sacs (synaptic vesicles) containing chemical substances referred to as "neurotransmittors". When they receive a strong positive charge they interpret this as a message to release. The sacs surrounding them burst and neurochemical transmitters flow out into the synaptic cleft. There they interact with receptors on adjacent neurones. These receptors highly specialised and understand messages only from particular types of neurochemicals. Only particular chemicals can "unlock" it and give it a message.

Many neuroscientists believe that the "break" in the brain leading to mental illness is a breakdown in neurotransmitter systems. The neurotransmitter system that carries norepinephrine as well as serotonin system is important to the study of mental illness, since there are many hints from pharmacological and neurochemical research that patients suffering from depression may suffer from a deficit of norepinephrine or serotonin. Although these 2 types of depression appears to be similar in their clinical symptoms, they are due to different chemical causes and likely to respond to different types of drugs.

Cited sources:
1. The broken brain, Nancy C. Andersen,M.D., Ph.D., Harper & Row, Publishers,
    New York 1984