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Introduction to NEUROANATOMY

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Introduction to NEUROANATOMY Michael T. Ingram, Jr., M.S., M.D. MTI Psychiatry, Inc. Simply Psych EDU Psychiatry and Neuroscience . The Cerebral Cortex is a mantle of gray matter covering the cerebral hemispheres . The cerebral cortex is well developed in higher mammals . Korbinian Brodmann (1909) organized cortex into areas based on cytoarchitectonic characteristics . Areas were numbered based on the order of prepared slides . 52 areas . Types of cortex: . Three-layered allocortex . Hippocampus . Piriform cortex . Six-layered neocortex . Majority of cerebral cortex . Four to Five layered paralimbic cortex (mesocortex) . Orbitofrontal cortex . Insula . Temporal pole . Parahippocampal gyrus . Cingulate gyrus • Gray Matter • Cell Bodies • Synapses • EX: Cortex, Nuclei • White Matter • Myelinated axons • Gray Matter • White Matter Layer of Neocortex Name Characteristics I Molecular Layer Primarily axons connecting local cortical regions II Small Pyramidal Layer Small-medium pyramidal cells connecting cortical areas III Medium Pyramidal Layer Small-medium pyramidal cells connecting cortical areas IV Granular Layer Mostly nonpyramidal cells, Receives most of the cortical input from the thalamus and is greatly expanded in primary sensory cortex V Large Pyramidal Layer Large pyramidal cells with long axons descending to subcortical structures, brain stem, and spinal cord Most prominent in motor cortex VI Multiform Layer Pyramidal cells projecting to thalamus Layers II, IV have greatest cell density and smallest cells Layers III,V have lowest cell density and largest cells with most dendritic ramification Evolutionary Model of Neuroanatomy By Paul Yakovlev (1948-1967) Median Zone (Yellow) Paramedian-limbic zone (Blue) Supralimbic Zone (Red) Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic zone (red). Source. Based on Yakovlev and Lecours 1967. • Hypothalamus Median Zone (Yellow) • Medial Thalamus Adjacent to Ventricles and Central canal • Periventricular Gray Matter Poorly myelinated • Amygdala Neurons with short axons projecting • Insular Cortex locally Mediates energy metabolism, homeostasis, peristalsis, respiration, and circulation Contains RAS and Thalamocortical projections that maintain consciousness and arousal while awake and sleep initiation and maintenance No lateralization of function Fully functional at birth Survival of the infant Paramedian-limbic zone (Blue) Supralimbic Zone (Red) Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic zone (red). Source. Based on Yakovlev and Lecours 1967. • Thalamic Nuclei Median Zone (Yellow) • Basal Ganglia Paramedian-limbic zone (Blue) • Caudate • Putamen More fully myelinated than median zone • Substantia Nigra Arranged in Nuclear structures • Subthalamic Nucleus • Globus Pallidus connected in series • Cingulate gyrus Limbic system • Insula Mediate posture, expression of emotion, • Orbitofrontal region emotional experience • Hippocampus Little lateral specialization • Parahippocampal gyri Present in reptiles Partially functional at birth, but becomes evident with smiling and crawling Disorders of motivation, mood, and affect are associated with this zone Supralimbic Zone (Red) Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic zone (red). Source. Based on Yakovlev and Lecours 1967. Median Zone (Yellow) Paramedian-limbic zone (Blue) Supralimbic Zone (Red) Outermost in the brain • Neocortex Neurons in this zone have long, well-myelinated • Lateral Thalamus axons that project via white matter tracts to more distant targets Mediates higher cortical functions as well as pyramidal neurons that project to the limbs, lips, and tongue Highly skilled, fine-motor movements evident in speech and hand control First expressed as pincer grasp and articulate speech First appeared in mammals and most well developed in humans Art, manufacturing, speech, writing, science Lateralized specialization of structure and function Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic zone (red). Source. Based on Yakovlev and Lecours 1967. • Neocortex Supralimbic Zone (Red) • Lateral Thalamus Expansion of neocortex in humans has been at the expense of a secure vasculature Poor collateral blood flow Border Zone infarctions Area of vulnerability to ischemia at margins of the lateral ventricles “Periventricular white matter disease” associated with depression, dementia, Binswanger’s disease Vulnerable to some of the most common neurological disorders associated with aging (stroke, Alzheimer’s) Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic zone (red). Source. Based on Yakovlev and Lecours 1967. Median Zone (Yellow) Paramedian-limbic zone (Blue) Supralimbic Zone (Red) Aphasia (inability to process language) • Neocortex Apraxia (inability to perform learned movement • Lateral Thalamus sequences) Agnosia (inability to recognize stimuli) Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic zone (red). Source. Based on Yakovlev and Lecours 1967. Evolutionary Model of Neuroanatomy By Paul Yakovlev (1948-1967) Median Zone (Yellow) Basic-life sustaining functions Problems with MZ responsible for disturbances in consciousness, metabolism, respiration, circulation Paramedian-limbic zone (Blue) Disorders of emotion, motivation, personality and anterograde amnesia (impairments in new learning) Supralimbic Zone (Red) Associated with most neuropsychiatric deficit syndromes Updated version of Yakovlev’s model of the nervous system demonstrating the median zone (yellow), paramedian-limbic zone (blue), and supralimbic Disorders of language, prosody, praxis, zone (red). recognition, visuospatial function, calculation, Source. Based on Yakovlev and Lecours 1967. executive function Heteromodal Prefrontal Motor Association Association Cortex Cortex (Supplemental motor Unimodal area, Premotor area Association Cortex Primary Sensory Primary Motor Cortex Cortex Brainstem, Subcortex Peripheral Sensory organs Limbic and Paralimbic Movement Environmental Regions & Behavior Stimuli (Sounds, light, touch, etc.) . Primary Motor Cortex . Origin of pyramidal motor system . Primary Sensory Cortex . First level cortical information processing in the brain (i.e., perception) . Unimodal Association Cortex . Second level information processing in the cerebral cortex after the primary sensory cortex (i.e., recognition) . Heteromodal Association Cortex . Highest level of information processing in the cerebral hemispheres . Posterior (Tertiary) – sensory integration with limbic and paralimbic input . Anterior (Quaternary) – Motor/Sensory integration and executive functioning . Lesions . Primary Motor Cortex . Contralateral Weakness . Hyper-reflexia . Extensor plantar response (Babinski) . Primary Sensory Cortex (perception) . Primary Somatosensory Cortex and Primary Visual Cortex . Contralateral sensory deficits . Primary Auditory Cortex . Bilateral Sensory deficits . Unimodal Association Cortex . Recognition deficits confined to the affected cortical sensory modality (agnosias) . Heteromodal Association Cortex . Posterior: Gerstmann Syndrome (alexia, agraphia, acalculia, right-left disorientation, finger agnosia, anomia, and constructional disturbances) . Anterior: Deficits in motor programming, memory retrieval, abstraction, and judgement . Decision making . Planning . Problem-solving . Thinking . Voluntary motor control . Cognition . Intelligence . Attention . Language processing and Orbital-frontal cortex comprehension DAMAGE: • Paralysis • Loss of spontaneity in social interactions • Mood changes • An inability to express language • Atypical social skills and personality traits Orbital-frontal cortex LATERALIZATION OF THE BRAIN Clinical Correlation Clinical Correlation Orbital-frontal cortex Frontal Lobe Syndromes Disinhibited—poor impulse control and inappropriate behavior Disorganized—memory deficits and poor planning Apathetic—unmotivated and paucity of spontaneous behavior Lateral prefrontal cortex: Predominantly, but not exclusively, involved in time integration and organizing functions, such as working memory, attention, cognitive functions DLPFC: Working memory, decision making, performance of goal directed behaviors Diminished activity in Depression, OCD Medial and ventral prefrontal cortices: Predominantly involved in emotional and social functions as control of impulse, mood, empathy, and judgement. Part of the PFC . Ventral region of frontal lobe . Integrates sensory and other information to calculate a reward . Controls impulsivity and decision making based on rewards . Receives multimodal inputs from the temporal association cortex, amygdala and hypothalamus as well as limbic components of the basal ganglia . Viewed as the highest integration center for emotional processing . The OFC seems to play a role in situations involving incentives/bonus/rewards and in conditions, where the subject has to make rapid alterations in behavior to accommodate the environmental changes. Experimental lesions of OFC in monkeys have shown impairment in reward–
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