Biological Context of Psychiatric Nursing Care

Biological Context of Psychiatric Nursing Care

Donald L. Taylor

Interest in the brain and human behavior is as old as the human race. Records dating back to 3000 BC in Egypt describe brain anatomy and various brain injuries. Currently the field of neuroscience is rapidly expanding and includes many disciplines that combine for a more complete understanding of the human brain and how it is integrated with the body and the human environment (Figure 5-1). All nurses should have a working knowledge of the normal structure and function of the brain, just as all nurses should know about the structure and function of the heart.

Structure and Function of the Brain

The brain weighs about 3 pounds. It is composed of trillions of groups of cells that have formed highly specific structures and sophisticated communication pathways that have changed over millions of years of evolution (Box 5-1). A brief review of key brain regions is presented in Figures 5-2 through 5-6 and in Box 5-2.



Temporal Lobes

Receive and process auditory information, involved in higher-order processing of visual information, involved in complex aspects of memory and learning, and are important in the comprehension of language

Associated with functions such as abstract thought and judgment

Clinical example: Damage to Wernicke area, which contains the mechanisms for the formulation of language, results in receptive, or sensory, aphasia, in which words are produced but their sequence is defective in linguistic content, resulting in paraphasia (word substitutions), neologisms (insertion of new and meaningless words), or jargon (fluent but unintelligible speech), and a general deficiency in the comprehension of language is noted. If the lesion occurs in the connection between Broca area and Wernicke area, conduction aphasia results, in which a person has poor repetition but good comprehension.



Limbic System


Consolidates recently acquired information about facts and events, somehow turning short-term memory into long-term memory

Contains large amounts of neurotransmitters

Hippocampal volume loss (atrophy) associated with major depressive episodes; the direct effects of this atrophy are not yet fully understood

Clinical example: Surgical removal of the hippocampus results in the inability to form new memories of facts and events (names of new acquaintances, day-to-day events, inability to remember why a task was begun), although long-term memory, intelligence, and the ability to learn new skills are unaffected. A similar memory problem is Korsakoff syndrome, in which patients have intact intelligence but cannot form new memories. They typically confabulate (make up answers to questions), which occurs when the hippocampus and surrounding areas are damaged by chronic alcoholism. This also is seen in Alzheimer disease, in which the memory loss is profound, and extensive cellular degeneration in the hippocampus is noted.


Generates emotions from perceptions and thoughts (presumably through its interactions with the hypothalamus and prefrontal cortex)

Contains many opiate receptors

Amygdala hypertrophy (enlargement) is associated with various depressive syndromes

Clinical example: Electrical stimulation of the amygdala in animals causes responses of defense, raging aggression, or fleeing. In humans the most common response is fear and its related autonomic responses (dilation of the pupils, increased heart rate, and release of adrenaline). Conversely, bilateral destruction of the amygdala causes a great decrease in aggression, and animals become tame and placid. This is thought to be another kind of memory dysfunction that impairs the ability to learn or remember the appropriate emotional and autonomic responses to stimuli.


“Little brain”

Full range of sensory inputs finds its way here and in turn projects to various sites in the brainstem and thalamus

Although it is extensively involved with the processing of sensory information, it also is part of the motor system and is involved in equilibrium, muscle tone, postural control, and coordination of voluntary movements

It is thought that, because of connections to other brain regions, the cerebellum may be involved in cognitive, behavioral, and affective functions

Clinical example: The malnutrition often accompanying chronic alcoholism causes a degeneration of the cerebellar cortex, resulting in the anterior lobe syndrome in which the legs are primarily affected, and the most prominent symptom is a broad-based, staggering gait and a general incoordination, or ataxia, of leg movements.

Blood-Brain and Blood-CSF Barriers

The brain develops and changes in utero and throughout the life span. This is known as neural plasticity. During adolescence the efficiency of the brain is refined by eliminating unneeded circuits, called synaptic pruning, and strengthening others. This process allows humans to have a brain that accommodates both its genetic potential and the environmental influences surrounding it.

The changing brain reacts to a variety of influences that can support health or promote illness, both before birth and across the life span. About 100 billion brain cells, or neurons, form groups or structures that are highly specialized. Neurotransmission is the process by which neurons communicate with each other through electrical impulses and chemical messengers.

This communication among neurons is carried out by chemical “first” messengers called neurotransmitters, and gives rise to human activity, body functions, consciousness, intelligence, creativity, memory, dreams, and emotion. Neurotransmission is a key factor in understanding how various regions of the brain function and how interventions, such as medications and other therapies, affect brain activity and human behavior.

Neurotransmitters are manufactured in the neuron and released from the axon, or presynaptic cell, into the synapse, which is the space between neurons. From there the neurotransmitters are received by the dendrite, or postsynaptic cell, of the next neuron. This neurotransmission process makes communication among brain cells possible (Figure 5-7).

Like a key inserted into a lock, each of these chemicals fits precisely into specific receptor cells (made of protein) embedded in the membranes of the axons and dendrites. These receptor cells then either open or close doors (ion channels) into the cell, allowing for the interchange of chemicals, such as ions like sodium (Na+), potassium (K+), and calcium (Ca2+).

This process, known as depolarization, changes the electrical charge of the cell. This change then triggers a cascade of chemical and electrical processes that are caused by a variety of chemicals called second messengers within the cell itself. The second messengers regulate the function of the ion channels, the production of neurotransmitters, and the release of neurotransmitters into the synapse—they continue the process of neurotransmission.

Depending on the chemical composition of the neurotransmitter, the signal it gives either excites the receiving cells, causing them to produce an action, or inhibits the receiving cells, which slows or stops an action. After release into the synapse and communication with receptor cells, the neurotransmitters are transported back from the synapse into the axon in a process called reuptake, where they are stored for future use or are inactivated (metabolized) by enzymes.

The nervous system cells are surrounded by myelin sheaths formed by specialized groups of cells called glial cells. These are support cells that insulate neurons, remove excess transmitters and ions from the extracellular spaces in the brain, provide glucose to some nerve cells, and direct the flow of blood and oxygen to various parts of the brain. Several chambers or ventricles within the brain carry cerebrospinal fluid (CSF). The CSF cushions, protects, and bathes the brain and spinal cord, carrying chemicals, nutrients, and wastes to and from the bloodstream.

Neurons are very specialized, and neurotransmitters perform vital functions in the normal working brain. Their absence or excess can play a major role in brain disease and behavioral disorders. A single neurotransmitter can affect other brain chemicals as well as several different subtypes of receptor cells, each located along tracts connecting different regions of the brain. Thus the same neurotransmitter can have one effect in one part of the brain and different effects in another part of the brain. Nearly all known neurotransmitters fall into one of two categories: small amine molecules (monoamines, acetylcholine, amino acids) and peptides. These are described in Table 5-1.



Amines are neurotransmitters that are synthesized from amino acid molecules such as tyrosine, tryptophan, and histidine. Found in various regions of the brain, amines affect learning, emotions, motor control, and other activities.    
Norepinephrine (NE) Derived from tyrosine, a dietary amino acid; located in brainstem (particularly locus ceruleus)
Effect: can be excitatory or inhibitory
Levels fluctuate with sleep and wakefulness. Plays a role in changes in levels of attention and vigilance. Involved in attributing a rewarding value to a stimulus and in regulation of mood. Plays a role in affective and anxiety disorders. Antidepressants block reuptake of NE into presynaptic cell or inhibit monoamine oxidase from metabolizing it.
Dopamine (DA) Derived from tyrosine, a dietary amino acid; located mostly in brainstem (particularly substantia nigra)
Effect: generally excitatory
Involved in control of complex movements, motivation, and cognition and in regulating emotional responses. Many drugs of abuse (e.g., cocaine, amphetamines) cause DA release, suggesting a role in sensation of pleasure. Involved in movement disorders seen in Parkinson disease and in many of the deficits seen in schizophrenia and other forms of psychosis. Antipsychotic drugs block DA receptors in postsynaptic cells.
Serotonin (5-HT) Derived from tryptophan, a dietary amino acid; located only in brain (particularly in raphe nuclei of brainstem)
Effect: mostly inhibitory
Levels fluctuate with sleep and wakefulness, suggesting a role in arousal and modulation of general activity levels of CNS,∗ particularly onset of sleep. Plays a role in mood and probably in delusions, hallucinations, and withdrawal symptoms of schizophrenia. Involved in temperature regulation and pain-control system of body. The hallucinogenic drug LSD acts at 5-HT receptor sites. Plays a role in affective and anxiety disorders. Antidepressants block its reuptake into presynaptic cells.
Melatonin Further synthesis of serotonin produced in pineal gland
Effect: mostly inhibitory
Induces pigment-lightening effects on skin cells and regulates reproductive and immune function.
Acetylcholine Synthesized from choline; located in brain and spinal cord but is more widespread in peripheral nervous system, particularly neuromuscular junction of skeletal muscle
Effect: can have an excitatory or inhibitory effect
Plays a role in sleep-wakefulness cycle. Signals muscles to become active. Alzheimer disease is associated with degeneration in acetylcholine neurons. Myasthenia gravis (weakness of skeletal muscles) results from reduction in acetylcholine receptors.
Amino Acids
Glutamate Found in all cells of body, where it is used to synthesize structural and functional proteins; also found in CNS, where it is stored in synaptic vesicles and used as a neurotransmitter
Effect: excitatory
Implicated in schizophrenia; glutamate receptors control the opening of ion channels that allow calcium (essential to neurotransmission) to pass into nerve cells, propagating neuronal electrical impulses. Its major receptor, NMDA, helps regulate brain development. This receptor is blocked by drugs (e.g., PCP) that cause schizophrenic-like symptoms. Overexposure to glutamate is toxic to neurons and may cause cell death in stroke and Huntington disease.
Gamma-aminobutyric acid (GABA) A glutamate derivative; most neurons of CNS have receptors
Effect: major transmitter for postsynaptic inhibition on CNS
Drugs that increase GABA function, such as benzodiazepines, are used to treat anxiety and epilepsy and to induce sleep.
Histamine Located in diencephalon, particularly hypothalamus (see Figure 5-4)
Effect: can be excitatory or inhibitory
May play a role in alertness and learning. Is being investigated as potential mechanism for side effects commonly associated with psychotropic medications (weight gain, hyperlipidemia). Same substance as involved with immunological/allergic responses.
Peptides are chains of amino acids found throughout the body. New peptides are continually being identified, with 100 neuropeptides active in the brain, but their role as neurotransmitters is not well understood. Although they appear in very low concentrations in the CNS, they are very potent. They also appear to play a “second messenger” role in neurotransmission; that is, they modulate messages of nonpeptide neurotransmitters through G protein–linked receptors.    
Endorphins, enkephalins, dynorphins, and endomorphins Widely distributed in CNS
Effect: generally inhibitory
The opiates morphine and heroin bind to these endogenous opioid receptors on presynaptic neurons, blocking release of neurotransmitters and thus reducing pain.
Substance P Spinal cord, brain, and sensory neurons associated with pain
Effect: generally excitatory
Found in pain transmission pathway. Blocking release of substance P by morphine reduces pain.

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Feb 25, 2017 | Posted by in NURSING | Comments Off on Biological Context of Psychiatric Nursing Care

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