Higher Mental Function.doc

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University of Ottawa
Anatomy and Physiology
Jacqueline Carnegie

Higher Mental Function -functional brain systems are networks of neurons that work together but span relatively large distances in the brain and cannot be localized to specific brain regions -i.e.: the limbic system and the reticular formation The Limbic System -includes the rhinencephalon (septal nuclei, cingulate gyrus, parahippocampal gyrus, dentate gyrus, and hippocampus) and the amygdala -acts as the emotional brain -the amygdala recognizes angry or fearful facia expressions, assesses danger, and elicits a fear response -the cingulate gyrus is involved in expressing emotions through gestures and in resolving mental conflicts when we are frustrated -odors trigger emotional reactions and memories The Reticular Formation -extends through the central core of the medulla oblongata, pons, and midbrain (brainstem) -composed from 3 broad columns along the length of the brain stem 1) the midline raphe nuclei 2) medial (large cell) group of nuclei 3) lateral (small cell) group of nuclei -individual reticular neurons project to the hypothalamus, thalamus, cerebral cortex, cerebellum, and the spinal cord -the reticular formation is ideal for governing the arousal of the brain as a a whole -the reticular formation also has a motor arm -some of its motor nuclei projects to motor neurons in the spinal cord via tha reticulospinal tracts and helps control skeletal muscles during coarse limb movements -other reticular motor nuclei (i.e.: vasomotor, cardiac, and respiratory centers of the medulla) are autonomic centres that regulate the visceral motor functions Reticular Activating System -certain reticular neurons send a continuous stream of impulses to the cerebral cortex, keeping the cortex alert and conscious and enhancing its excitability -impulses from all the great ascending sensory tracts synapse with RAS neurons, keeping them active and enhancing their arousing effect on the cerebrum -RAS acts as a filter for the flood of sensory inputs -repetitive, familiar, or weak signals are filtered out -unusual, significant, or strong impulses reach consciousness -RAS is inhibited by sleep centers, depressed by alcohol / sleep-inducing drugs / trangquilizers -damage may result in permanent coma Brain Wave Patterns and the EEG -normal brain function involves continuous electrical activity of neurons -an electroencephalogram records some aspects of this activity -electrodes are placed on the scalp and the electrical potential differences is measured between various cortical areas -the patterns of neuronal electrical activity are known as brain waves -generated by synaptic activity at the surface of the cortex (not action potentials in the white matter) -each person's brain wave patterns are unique -wave frequency is expressed in Hz (the number of peaks per second) -the amplitude of a brain wave reflects the synchronous activity of many neurons and not the degree of electrical activity of individual neurons -typically, brain waves are complex and low amplitude -brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body -EEGs are used from diagnosing epilepsy, sleep disorders, and in research on brain function -a flat EEG is clinical evidence of brain death Alpha Waves - 8-13 Hz -relatively regular and rhythmic, low-amplitude, synchronous waves -indicate a brain this is idling (a calm, relaxed state of wakefulness) Beta Waves - 14-30 Hz -rhythmic waves -not as regular as alpha waves -higher frequency than alpha waves -occur when we are mentally alert (i.e.: concentrating on a problem or a visual stimulus) Theta Waves - 4-7 Hz -more irregular than alpha waves -common in children -abnormal in adults; may appear when concentrating Delta Waves - <4 Hz -high amplitude waves seen during deep sleep and when the reticular activating system is damped (i.e.: anesthesia) -in awake adults, this indicates brain damage Epilepsy -loss of consciousness, falling stiffly, uncontrollable jerking -epileptic seizures reflect a torrent of electrical discharges of groups of brain neurons, such that not other messages can get through -epilepsy is not associated with intellectual impariment -occurs in 1% of the population -absence seizures (petit mal) are mild forms of epileptic seizures where expression goes blank and consciousness disappears -typically seen in children -grand mal seizures (tonic-clonic) involve loss of consciousness -bones may be broken due to intense muscle contractions -loss of bowel / bladder control -can be controlled by anticonvulsive drugs -valproic acid enhances GABA and is a drug of choice -vagus nerve stimulators can be implanted under the skin of the chest and keeps electrical activity of the brain from become chaotic Consciousness -encompasses conscious perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (i.e.: memory, logic, judgment, perseverance, etc.) -consciousness is determined on a continuum that grades behaviour in response to stimuli as: -alertness -drowsiness / lethargy (leads to sleep) -stupor -coma -alertness is the highest state of consciousness and coma is the most depressed -consciousness involves simultaneous activity of large areas of the cerebral cortex -consciousness is superimposed on other types of neural activity -specific neurons and neuronal pools are involved in localized activities and in cognition -consciousness is holistic and interconnected -information for though can be claimed from many locations in the cerebrum simultaneously -e.g.: retrieval of a memory is triggered by a smell, a place, a person, etc. Types of Sleep -sleep is defined as a state of partial unconsciousness from which a person can be aroused by stimulation -coma sleep is a state of unconsciousness from which a person cannot be aroused -cortical activity is depressed during sleep -brain stem functions (respiration, heart rate, blood pressure, etc.) and environmental monitoring continue during sleep -the 2 major types of sleep are non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep and are defined in terms of their EEG patterns -we pass through 4 stages of NREM sleep in the first 30-45 minutes of sleep (stages 3 and 4 is slow-wave sleep) -we slip into deeper sleep and the frequency of the EEG waves decline, but amplitude increases -blood pressure and heart rate decrease with deeper sleep -NREM stages include:
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