THE ORGANIZATION OF THE NERVOUS SYSTEM AND PSYCHOPATHOLOGY AS IT IS RELATED TO ADDICTION In this paper, we will show how some basic principles of the structure and function of the nervous system can account for a variety of disorders of mind and behavior. We will illustrate each principle with an example from psychopathology, using this term loosely to mean any disorder of mind or behavior and addiction.
(see Luria, 1993; Gardner, 1995; Kolb and Whishaw, 1998; Adams and Victor, 1991; Kandel and Schwartz, 1991, for a more detailed treatment).
NEURONS~ SYNAPSES~ AND NEUROTRANSMITTERS Neurons are the "units" of the nervous system. Neurons communicate with one another by releasing neurotransmitter substances into the synapse, the gap separating one neuron from another (see Figure 19-3B). These transmitters either increase (excite) or decrease (inhibit) the activity of the other neurons. A simple example of synaptic function is strychnine poisoning. Strychnine is a highly toxic substance sometimes used in rat poison. It is, on rare occasions, eaten by children. Strychnine prevents inhibition at synapses. As a result, the delicate balance between excitation and inhibition in the nervous system is disturbed. The result is uncontrolled activity of the nervous system, manifested by a progression from irritability, to twitching, to seizures, to death due to spasm of the muscles responsible for breathing. Defects in the basic structure and function of synapses have been suggested as causes of some of the major mental illnesses.
You will recall branes (meninges) covering the brain. Much brain pathology originates in the supportive tissue, and not in the neurons themselves. More than 50 percent of the tumors (growths produced by an abnormal, uncontrolled multiplication of cells) originating in the brain involve the glia, and 15 percent involve the meninges. These tumors produce symptoms by destroying neighboring neural tissue, displacing it, or causing increased pressure in the skull, which interferes with circulation in the brain. Multiple sclerosis is a disorder of the glial cells which manufacture and maintain the myelin sheath that surrounds the axons of many neurons in the central nervous system. Some researchers believe that multiple sclerosis is caused by a virus that specifically attacks the myelin-producing glial.
The destruction of myelin leads to failure to conduct nerve impulses in the afflicted axons. The pathology tends to appear in neighboring axons, the result being a characteristic "plaque" (mass of scar tissue around the damaged axons). The symptoms of this usually progressive disease vary with the particular sites that are affected: weakness or loss of sensation in arms or legs are common, as are disorders in eye movement.
Infections of the supportive tissue can produce pathological symptoms. And, of course, blood clots in the arteries feeding the brain can deny oxygen and nutrients to the part of the brain served by the artery in question, causing a stroke (damage to the affected area). Damage can also be produced by rupture of a blood vessel in the brain (hemorrhage). Finally, the brain and spinal cord have their own special circulatory system, which if damaged can result in pathological symptoms. This circulatory system is filled with a clear fluid (cerebrospinal fluid) that is secreted by cells in the brain and that eventually re-enters the blood supply. This system is of particular importance in neuropathology because tumors and other types of damage may obstruct the circulation of this fluid and cause a build-up of pressure in the skull. Headache, drowsiness, or loss of consciousness are common consequences of such a build-up in pressure.