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1H06 Anatomy & Physiology: CNS – Cortex and Diencephalon.docx

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Health Sciences
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Alexander Ball

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CNS – Cortex and Diencephalon The Diencephalon  Forms central core of brain tissue superior to midbrain  Contains nuclei involved in sensory and motor processing between higher and lower brain centers.  Extends from brain stem to cerebrum and surrounds third ventricle; includes thalamus, hypothalamus, and epithalamus Thalamus  Makes up 80% of diencephalon, consists of paired oval masses of gray matter organized into nuclei with interspersed tracts of white matter  Intermediate mass joins right and left halves of thalamus in 70% of brains  Internal capsule – thick band of white matter lateral to thalamus  Thalamus is major relay station for most sensory impulses that reach primary sensory areas of cerebral cortex from spinal cord and brain stem  Contributes to motor functions by transmitting info from cerebellum and basal nuclei to primary motor area of cerebral cortex.  Relays nerve impulses between cerebrum areas and in maintenance of consciousness Seven major groups of nuclei on each side of thalamus: 1. Anterior nucleus a. Receives input from hypothalamus and sends output to limbic system, functions in emotions and memory 2. Medial nuclei a. Receive input from limbic system and basal nuclei and send output to cerebral cortex, functions in emotions, learning, memory, and cognition 3. Lateral group a. Nuclei receive input from limbic system, superior colliculi, and cerebral cortex and send output to cerebral cortex b. Lateral dorsal nucleus – expression of emotions c. Lateral posterior nucleus and pulvinar nucleus – integrate sensory information 4. Ventral group a. Ventral anterior nucleus – receives input from basal nuclei and sends output to motor areas of cerebral cortex (movement control) b. Ventral lateral nucleus – receives input from cerebellum and basal nuclei, sends output to motor areas of cerebral cortex (movement control) c. Ventral posterior nucleus relays impulses for somatic senses (touch, pressure, vibration, itch) d. Lateral geniculate nucleus relays visual impulses e. Medial geniculate nucleus relays auditory impulses 5. Intralaminar nuclei – onnects with reticular formation, cerebellum, basal nuclei, and wide areas of cerebral cortex (arousal) 6. Midline nucleus – band adjacent to third ventricle (memory and olfaction) 7. Reticular nucleus – surrounds lateral aspect of thalamus (monitors, filters, and integrates activities of other thalamic nuclei) Hypothalamus  Controls and integrates ANS activities including contraction of smooth and cardiac muscle and secretion of glands  Production of hormones (releasing and inhibiting)  Regulation of emotional and behavioural patterns (rage, aggression)  Regulation of eating and drinking  Control of body temperature  Regulation of circadian rhythms and states of consciousness  Inferior to thalamus, composed of dozen nuclei in four regions: 1. Mammillary region a. Adjacent to midbrain b. Has mammillary bodies and posterior hypothalamic nuclei 2. Tuberal region a. Includes dorsomedial nucleus, ventromedial nucleus, and arcuate nucleus b. Infundibulum connects pituitary gland to hypothalamus c. Median eminence encircles infundibulum 3. Supraoptic region a. Contains paraventricular nucleus, supraoptic nucleus, anterior hypothalamic nucleus, suprachiasmatic nucleus b. Axons from paraventricular and supraoptic nuclei form hypothalamohypophyseal tract 4. Preoptic region a. Participates with hypothalamus in regulating certain autonomic activities b. Contains medial and lateral preoptic nuclei Epithalamus  Consists of pineal gland and habenular nuclei  Pineal gland – (small, third ventricle, secretes melatonin (sleepiness))  Habenular nuclei – olfaction Circumventricular Organs  Lie in wall of third ventricle, monitor chemical changes in blood because they lack blood-brain barrier  Include part of hypothalmus, pineal gland, pituitary gland, and others  Coordinate homeostatic activities of endocrine and nervous systems (regulation of blood pressure, fluid balance, hunger, and thirst)  Sites of entry into brain of HIV The Cerebrum  Seat of intelligence  Ability to read, write, and speak, make calculations and compose music  Outer cerebral cortex, internal white matter, gray matter nuclei within white matter Cereral Cortex  Region of gray matter in outer rim of cerebrum  Contains billions of neurons arranged in layers  During brain growth, cortical region folds on itself, folds called gyri  Deepest grooves between folds are known as fissures; shallower grooves between folds are sulci Lobes of Cerebrum  Frontal, parietal, temporal, occipital  Central sulcus separates frontal lobe from parietal lobe  Lateral cerebral sulcus separates frontal lobe from temporal lobe Cerebral White Matter 1. Association tracts – axons conduct nerve impulses between gyri in same hemisphere 2. Commissural tracts – axons conduct nerve impulses from gyri in one cerebral hemisphere to corresponding gyri in other cerebral hemisphere a. Three important groups of commissural tracts are corpus callosum, anterior commissure, and posterior commissure 3. Projection tracts – axons conduct nerve impulses from cerebrum to lower parts of CNS or from lower parts of CNS to cerebrum a. Ex. Internal capsule (contains both ascending and descending axons) Basal Nuclei  Three nuclei collectively named  Two side-by-side are globus pallidus (closer to thalamus)  Putamen (closer to cerebral cortex)  Together they are called lentiform nucleus.  Third is caudate nucleus  Claustrum – function may involve visual attention, thin sheet of gray matter lateral to putamen  Basal nuclei initiate and terminate attention, memory, planning Limbic System  Limbic lobe – rim of cerebral cortex o Includes cingulate gyrus and parahippocampal gyrus  Dentate gyrus – between hippocampus and parahippocampal gyrus  Amygdala – neuron groups close to tail of caudate nucleus  Septal nuclei – within septal area formed by regions under corpus callosum and paraterminal gyrus  Mammillary bodies – round masses close to midline near cerebral peduncles  Anterior nucleus and medial nucleus – participate in limbic circuits  Olfactory bulbs – flattened bodies of olfactory pathway Limbic System is sometimes called emotional brain because it plays primary roles in range of emotions, including pain, pleasure, docility, affection, and anger. Functional Organization of Cerebral Cortex  Sensory areas – involved in perception (conscious awareness of sensation)  Motor areas – execution of voluntary movements  Association
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