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SECOND REVISED M07_EBY6927_02_SE_C07.QXD 12/17/07 12:02 PM Page 95 Chapter 7 Psychobiology and Psychopharmacology 95 TABLE 7-1 Brain Anatomy and Function BRAIN STRUCTURE FUNCTION Cerebral Cortex IMPLICATIONS FOR MENTAL DISORDERS The frontal lobes are affected in schizophrenia, which causes disordered thought processes, lack of motivation. Frontal Lobes Prefrontal Area Prefrontal area controls thought, inhibition, goal-oriented behavior. Motor Cortex Motor cortex controls voluntary movement. Pyramidal System Pyramidal system or corticospinal tract affects voluntary movement. Extrapyramidal System Extrapyramidal system affects movement patterns, automatic motor functioning of walking, and inhibits lower motor neurons from overactivity (involuntary movement). Basal Ganglia In the basal ganglia, complex motor skills (driving a car, activities of daily living [ADLs]) become so memorized that the ability to perform them persists even after damage to memory in the frontal lobes. Abnormalities in the motor area (for example, Parkinson’s disease) cause movement disorders: rigidity, resting tremor, slow movement, shuffling gait, sudden jerky movement, and athetosis (meaningless unintentional motions). These movement disorders can also be medication side effects (called extrapyramidal side effects). Temporal Lobes Auditory receptive and auditory association areas, olfactory function, language expression and interpretation Aphasia (receptive or expressive) is caused by damage in the temporal lobes. Parietal Lobes Sensory association Occipital Lobes Visual reception and visual association Damage to occipital lobes can cause blindness. Controls feeling pleasure, feeding and drinking behavior, the fight or flight response, aggression, submission, memory, body temperature, sexual behavior, emotions, and motivation for behavior. It is responsible for physical reactions to emotions. Limbic system also interprets olfactory sensations. Hippocampus converts short-term memories to long term.Thalamus also has sensory relaying and stimulus filtering functions. Schizophrenia decreases limbic system function (anhedonia, polydipsia [an abnormal, persistent increase in thirst], loss of motivation). Cocaine may stimulate limbic system to provide pleasure. Thiamine deficiency in alcoholics (Korsakoff’s syndrome) affects limbic function and causes loss of short-term memory. Hippocampus degenerates in Alzheimer’s disease. Most of brain dopamine is synthesized here. Reduced dopamine activity causes the extrapyramidal movement disorders of Parkinsonism. Increased dopamine activity in schizophrenia. Limbic System Refers to limbic lobe and structures that function with it: hippocampus, amygdala, thalamus, hypothalamus, brainstem nuclei, autonomic system Brainstem Midbrain (continued) SECOND REVISED M07_EBY6927_02_SE_C07.QXD 96 Unit I 12/17/07 12:02 PM Page 96 Foundations of Mental Health Nursing TABLE 7-1 Brain Anatomy and Function (continued) BRAIN STRUCTURE FUNCTION IMPLICATIONS FOR MENTAL DISORDERS Pons Conducts motor and posture information to cerebellum. Controls reflexes. Norepinephrine is made in the pons. Norepinephrine activity is decreased in depression and increased in schizophrenia. Medulla Oblongata The medulla controls respiration, regulation of blood pressure, partial regulation of heart rate, vomiting, and swallowing. Cerebral motor fibers collect here in the shape of pyramids. Here the motor fibers that begin in the cerebral cortex cross to the opposite side of the corticospinal motor pathway. Damage to the medulla can stop spontaneous breathing.The fact that motor fibers cross at the medulla explains why a stroke affects the movement of the opposite side of the body from where the brain damage occurred. Reticular Formation Sensory input is integrated in the reticular formation and conducted to other brain areas. It affects sensory, motor, and visceral functions.The RAS allows screening/filtering of stimuli so the brain does not have to react to all stimuli. RAS controls the sleepwake cycle. Reticular formation may be involved in attention deficit disorder (may be due to an inability to filter sensory stimuli normally). If the RAS is disrupted and a person cannot sleep, psychosis can result. Cerebellum mainly coordinates muscle activity and function, and maintains equilibrium. It may be involved in cognitive and behavioral functions because of its connections to other brain areas. Cerebellar disorders cause ataxia (awkward gait and uncoordinated intentional movement), intention tremor, decreased reflexes, and nystagmus. Cerebellar ataxia may be caused by malnutrition in severe, prolonged alcoholism. Reticular Activating System (RAS) Cerebellum at relieving client symptoms, and not because their mechanism of action is fully understood. Figure 7-2. ■ Electron micrograph of brain neurons. Source: Photo Researchers, Inc. NEUROTRANSMITTERS Neurotransmitters are chemical messengers that conduct impulses from one neuron to the next. Figure 7-3 ■ illustrates neurotransmitter function. Review it carefully because it is the basis for understanding treatment of mental disorders with psychotropic drugs. Human consciousness, behavior, learning, memory, emotion, and creativity are all the result of physiological brain functions. Neurotransmission is the communication between neurons conducted by neurotransmitter chemicals. Neurotransmission must occur for the brain to perform normally (Keltner, 2000). The building materials for neurotransmitters are brought into the body in food. The intake of adequate