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Lecture 9

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Byron Williston

STRUCTURE AND FUNTION OF THE HUMAN BRAIN BOX  inside the skull the brain is enveloped within three layers of non neural tissue, membranes referred to as meninges  viewed from the top the brain is divided by a midline fissure into two mirror image cerebral hemispheres together constituting most of the cerebrum.  The cerebrum is the thinking centre of the brain, which includes the cortex and sub cortex structures such as the basal ganglia and limbic system.  The major connections between the two hemispheres is a band of nerve fibres called the corpus callosum  The upper side and some of the lower surfaces of the hemispheres form the cerebral cortex  The corxt consist of 6 layers of tiglhy packed neuron cell bodies with many short unsheathed interconnecting processes  These neurons estimated to # 10-15 billion make up a thin outer covering the so called grey matter of the brain  The cortex is vastly convoluted; the ridges are called gyri and the depressions between them suici, several distinct areas called lobes  The frontal lobe lies in front of the central suclus, the parietal lobe is behind it and above the later suclus , the temporal lobe is located below the lateral suclus and the occipital love lies behind the parietal and temporal lobes  Vision in the occipital; discrimination of sounds in the temporal; reasoning and other higher mental processes as well as the regulation of fine voluntary movement in the frontal; initiation of movements of the skeletal musculature in a band in front of the central sulcus; and receipt of sensations of touch, pressure, pain, temperature and body position from skin, muscles, tendons, and joints in a band behind the central sulcus  The two hemispheres of the brain have different functions. The left hemisphere which generally controls the right half of the body cuz of the crossing over of motor and sensory fibres is responsible for speech and according to some neuropsychologists for analytical thinking in right handed ppl and in a fair # of left handed ppl as well  The right hemisphere controls the left side of the body, discerns spatial relations and patterns and is involved in emotion and intuition  The two hemispheres communicate with each other constantly via the corpus callosum  The grey matter of the cerebral cortex does not extend throughout the interior of the brain.  Much of the interior is white matter made up of large tracts or bundles or myelinated (sheathed) fibres that connect cell bodies in the cortex with those in the spinal cord and other centres lower in the brain  These centres are pockets of grey matter referred to as nuclei. The nuclei serve both as way stations connecting tracts from the cortex with other ascending and descending tracts and as integrating motor and sensory control centres.  Some cortical cells project their long fibres or axons to motor neurons in the spinal cord but others project them only as far as these clusters of interconnecting neuron cell bodies.  Four masses are deep within each hemisphere called collectively the basal gangl
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