The Biologic Foundations of Psychiatric Nursing Chapter 8

Biological Basis of Behavior Most human behaviors have a biological basis. Symptom expression = behavioral symptoms = brain dysfunction

Foundation of Biological Basis of Behavior Animal modeling – Resembles humans in structure, function or genetics – Can induce disorders – Usually rats, mice Genetics – Populations genetics – Risk factors

Risk Factors Increased risk for developing a disorder May be genetic, biological, psychologic or social

Current Approaches to Studying Neuroanatomy and Neurophysiology Comparative – compared with other life forms Developmental – changes in nervous system throughout the life span Cytoarchitectonic – distribution and arrangement of cells within various parts of brain Chemoarchitecture – identification of neurotransmitters or chemicals Functional – localization of functioning

Plasticity Ability of the brain to change Compensates for loss of function in specific area Nerve signals may be rerouted. Cells learn a new function. Nerve tissues may be regenerated.

Structural Neuroimaging Allows for visualization of the brain Commonly used techniques – Computed tomography (CT) X-rays and computers Iodinated contrast materials administered IV – Magnetic resonance imaging (MRI) Place patient in long tube with magnets Can reconstruct three-dimensional structures More costly and complicated than CT

Functional Neuroimaging Measurement of physiologic activities Two primary imaging procedures (Both require administration of radioactive materials.) – Positron emission tomography (PET) – Single photon emission computed tomography (SPECT) – Patient can perform functions during this time.

Neuroanatomy of the CNS Cerebrum Left and right hemispheres Lobes of the brain – Frontal – Parietal – Temporal – Occipital – Association Cortex

Neuroanatomy Subcortical Structures Basal ganglia Limbic system Hippocampus Thalamus Hypothalamus Amygdala Limbic midbrain nuclei

Neuroanatomy Other Important CNS Structures Extrapyramidal system Pineal body Locus ceruleus Cerbebellum

Autonomic Nervous System ( Fig. 8.7) Neurons of ANS – Efferent or motor system nerves (nerves moving away from CNS) – Afferent or sensory (nerves moving toward CNS) Sympathetic Parasympathetic

Neurons and Nerve Impulses (Fig. 8.8) Soma – cell body – nucleus – ribosomes – endoplasmic reticulum – Golgi apparatus – vesicles – lysomes – mitrochodria Axons – conducts impulses Dendrites – receives impulses

Synaptic Transmission Neurotransmitters - Small molecules directly or indirectly responsible for opening or closing ion channels Neuromodulators - Chemical messengers that make the cell membrane more or less susceptible to effects of primary neurotransmitter Influx of CA ++ into the neuron stimulates release of neurotransmitters into synapse. Receptors - Proteins for specific neurotransmitter, “lock and key”

Fate of Neurotransmitter After Action Removed by natural diffusion Reuptake into presynaptic terminal

Receptors Sensitivity can change, developing either a greater or lesser response to the neurotransmitter. Receptor subtypes – Each major neurotransmitter has several different subtypes for the chemical, allowing for different effects on the brain. – Each major neurotransmitter has several different subtypes (e.g., Dopamine, D 1, D 2, etc.).

Neurotransmitter Criteria Synthesized inside the neuron Present in the presynaptic terminal Released into the synaptic cleft, causing a particular effect on the postsynaptic receptors An exogenous form of the chemical is administered as a drug causes identical action. Chemical is removed from the synaptic cleft by a specific mechanism.

Neurotransmitters Excitatory – causes activity to occur Inhibitory – causes activity to decrease

Cholinergic Neurotransmitter Acetylcholine (ACh) Primary neurotransmitter of parasympathetic nervous system Part of sympathetic system Excitatory neurotransmitter Follow diffuse projections throughout the cerebral cortex and limbic system ACh involved in higher intellectual functioning and memory

Cholinergic Receptor Muscarinic receptors – Many psychiatric medications block the muscarinic receptors (anticholinergic). – Blocking the effects causes common side effects, including: dry mouth, blurred vision constipation, urinary retention, and tachycardia Nicotinic receptors

Biogenic Amines Synthesized from tyrosine – Dopamine – Norepinephrine – Epinephrine Synthesized from tryptophan – Serotonin Synthesized from histidine – Histamine

Neurotransmitters Acetylcholine – High intellectual functioning Dopamine – Mesocortical and Mesolimbic Cognition, memory, emotion, auditory reception – Nigrostriatal Influences extrapyramidal system Subserve voluntary movement Allows involuntary movement – Tuberoinfundibular Endocrine functions

Dopamine (DA) Excitatory neurotransmitter Involved in cognition, motor and neuroendocrine functions Decreased in Parkinson’s, increased in schizophrenia Pathways (Figure 8.11) – Mesocortical, mesolimbic – Nigrostriatal – Tuberoinfundibular

Dopamine Receptors Five subtypes D 1 and D 5 - cortex, hippocampus and amygadala D 2 found in nigrostriatal system D 4 found mainly in cortex

Norepinephrine Widely distributed in the peripheral nervous system Excitatory neurotransmitters play a major role in mood states. Decreased NE associated with depression, increased NE associated with mania Pathways are named “noradrenergic” and are less delineated than dopamine pathways. Pathways in locus cereulus so involve in sleep, wake

Neurotransmitters Norepinephrine (Fig. 8.12) – Sympathetic nervous system functions – Sleep, wakefulness – Reinforce learning Serotonin (5-HT) (Fig. 8.13) – Sleep, wakefulness – Control of food intake, hormone secretion, sexual behavior, mood and emotion, thermoregulation

Serotonin (5-HT) Excitatory neuron distributed within the cerebral cortex, limbic system, an basal ganglia, hypothalamus and cerebellum. Involved in regulation of emotion, cognition, sensory perceptions, sleep and appetite. Involved in control of food intake, hormone secretin, sexual behavior, thermoregulation and cardiovascular regulation Numerous subtypes of receptors

Histamine Recently identified as a neurotransmitter Originates in hypothalamus and projects to all major structures in cerebrum, brain and spinal cord Functions not well known Blocking produces side effects, such as sedation, weight gain and hypotension.

Aminobutyric Acid (GABA) Inhibitory transmitter Pathways almost exclusive in CNS, hypothalamus, hippocampus, basal ganglia, spinal cord and cerebellum Receptors: – GABAA – GABAB

Neurotransmitters Histamine – Autonomic and neuroendocrine regulation – Blocking – causing sedation and weight gain GABA – Control of neuronal excitement – Inhibitory Glutamate – Excitatory Neuropeptides

New Fields of Study Psychoendocrinology Psychoimmunology Chronobiology Diagnostic Approaches

Neurophysiologic Procedures Electroencephalography (EEG) Polysomnography Others