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Chapter: Psychiatric Mental Health Nursing : Neurobiologic Theories and Psychopharmacology


Approximately 100 billion brain cells form groups of neu-rons, or nerve cells, that are arranged in networks.


Approximately 100 billion brain cells form groups of neu-rons, or nerve cells, that are arranged in networks. These neurons communicate information with one another by sending electrochemical messages from neuron to neuron, a process called neurotransmission. These electrochemical messages pass from the dendrites (projections from the cell body), through the soma or cell body, down the axon (long extended structures), and across the synapses (gaps between cells) to the dendrites of the next neuron. In the nervous system, the electrochemical messages cross the synapses between neural cells by way of special chemical messengers called neurotransmitters.


Neurotransmitters are the chemical substances manu-factured in the neuron that aid in the transmission of infor-mation throughout the body. They either excite or stimulate an action in the cells (excitatory) or inhibit or stop an action (inhibitory). These neurotransmitters fit into specific recep-tor cells embedded in the membrane of the dendrite, just like a certain key shape fits into a lock. After neurotransmit-ters are released into the synapse and relay the message to the receptor cells, they are either transported back from the synapse to the axon to be stored for later use (reuptake) or metabolized and inactivated by enzymes, primarily mono-amine oxidase (MAO) (Figure 2.3).

These neurotransmitters are necessary in just the right proportions to relay messages across the synapses. Studies are beginning to show differences in the amount of some neurotransmitters available in the brains of people with certain mental disorders compared with people who have no signs of mental illness (Figure 2.4).

Major neurotransmitters have been found to play a role in psychiatric illnesses as well as in the actions and side effects of psychotropic drugs. Table 2.1 lists the major neu-rotransmitters and their actions and effects. Dopamine and serotonin have received the most attention in terms of the study and treatment of psychiatric disorders (Tecott & Smart, 2005). The following sections discuss the major neurotransmitters associated with mental disorders.


Dopamine, a neurotransmitter located primarily in the brain stem, has been found to be involved in the control of complex movements, motivation, cognition, and regula-tion of emotional responses. It is generally excitatory and is synthesized from tyrosine, a dietary amino acid. Dop-amine is implicated in schizophrenia and other psychoses as well as in movement disorders such as Parkinson’s dis-ease. Antipsychotic medications work by blocking dop-amine receptors and reducing dopamine activity.

Norepinephrine and Epinephrine

Norepinephrine, the most prevalent neurotransmitter in the nervous system, is located primarily in the brain stem and plays a role in changes in attention, learning and memory, sleep and wakefulness, and mood regulation. Norepinephrine and its derivative, epinephrine, are also known as noradrenaline and adrenaline, respectively. Excess norepinephrine has been implicated in several anx-iety disorders; deficits may contribute to memory loss, social withdrawal, and depression. Some antidepressants block the reuptake of norepinephrine, whereas others inhibit MAO from metabolizing it. Epinephrine has lim-ited distribution in the brain but controls the fight-or-flight response in the peripheral nervous system.


Serotonin, a neurotransmitter found only in the brain, is derived from tryptophan, a dietary amino acid. The function of serotonin is mostly inhibitory, and it is involved in the control of food intake, sleep and wakefulness, temperature regulation, pain control, sexual behavior, and regulation of emotions. Serotonin plays an important role in anxiety and mood disorders and schizophrenia. It has been found to con-tribute to the delusions, hallucinations, and withdrawn behavior seen in schizophrenia. Some antidepressants block serotonin reuptake, thus leaving it available longer in the synapse, which results in improved mood. 


The role of histamine in mental illness is under investiga-tion. It is involved in peripheral allergic responses, control of gastric secretions, cardiac stimulation, and alertness. Some psychotropic drugs block histamine, resulting in weight gain, sedation, and hypotension.


Acetylcholine is a neurotransmitter found in the brain, spinal cord, and peripheral nervous system, particularly at the neuromuscular junction of skeletal muscle. It can be excitatory or inhibitory. It is synthesized from dietary cho-line found in red meat and vegetables and has been found to affect the sleep–wake cycle and to signal muscles to become active. Studies have shown that people with Alzheimer’s disease have decreased acetylcholine-secreting neurons, and people with myasthenia gravis (a musculardisorder in which impulses fail to pass the myoneural junction, which causes muscle weakness) have reduced acetylcholine receptors.


Glutamate is an excitatory amino acid that at high levels can have major neurotoxic effects. It has been implicated in the brain damage caused by stroke, hypoglycemia, sustained hypoxia or ischemia, and some degenerative dis-eases such as Huntington’s or Alzheimer’s.

Gamma-Aminobutyric Acid

Gamma-aminobutyric acid (γ-aminobutyric acid, or GABA), an amino acid, is the major inhibitory neurotrans-mitter in the brain and has been found to modulate other neurotransmitter systems rather than to provide a direct stimulus (Plata-Salaman, Shank, & Smith-Swintosky, 2005). Drugs that increase GABA function, such as benzo-diazepines, are used to treat anxiety and to induce sleep.

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