Cerebral Hemispheres.docx

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Department
Anatomy and Cell Biology
Course
Anatomy and Cell Biology 3319
Professor
Kem Rogers
Semester
Fall

Description
Cerebral Hemispheres Cerebrum • Most rostral portion of the brain • Made of 2 cerebral hemispheres • Account for 83% of total brain mass • Functions o Sensory reception and processing o Motor output and processing o Association areas to process complex interactions between brain areas o Perception and interpretation o Cognitive function including decision making • Cover the diencephalon & rostral brain stem • Various fissures separate the major portions of the brain o Transverse cerebral fissure: separates the cerebral hemispheres from cerebellum inferiorly o Median longitudinal fissure: separates the right & left cerebral hemispheres • Composed of a o Superficial cerebral cortex of gray matter – containing neuron cell bodies o Cerebral white matter internal to it – deep layer containing fibres which connect cell bodies – appear white because of myelin sheaths (fatty insulating material) o Deep gray matter of the cerebrum within white matter – deep collection of neuron cell bodies Lobes of Cerebral Cortex • Sulci: many shallow grooves on the surface of cerebral hemispheres • Gyri: twisted ridges of brain tissue between sulci o Sheet arrangement o Highly folded to increase surface area • Deeper sulci divide into 5 major lobes: o Frontal  Located deep to the frontal bone  Fills anterior cranial fossa  Extends posteriorly to central sulcus: separates it from the parietal lobe  Precentral gyrus: containing primary motor cortex lies anterior to the central sulcus  Functions: plan, initiate & enact motor movement - eye movement & speech production  Most anterior region performs high-functioning cognitive functions: thinking, planning & decision making, working memory & other executive functions o Parietal  Deep to parietal bones  Extends posteriorly to the central sulcus to parieto- occipital sulcus  Lateral sulcus forms its inferior boundary  Post-central gyrus just posterior to central sulcus  Contains primary somatosensory cortex  Processes sensory stimuli allowing • Conscious awareness of general somatic sensation • Special awareness of objects, sound & body parts • Understanding of speech o Occipital  Lies deep to occipital bone  Forms most posterior portion of cerebrum  Separated from parietal lobe by parieto-occipital sulcus on medial surface of hemisphere  Contains visual cortex o Temporal  Lateral side of hemisphere  Lies in the middle cranial fossa deep to temporal bone  Separated from overlying parietal & frontal lobes by deep lateral sulcus  Contains auditory cortex & olfactory cortex   Functi o ns in recognition of objects, words, faces & in language comprehension o Insular  Buried deep within lateral sulcus & forms part of its floor  Covered by parts of temporal, parietal & frontal lobes  Visceral sensory cortex for taste & general visceral sensations  Peeling back along lateral fissure Functional Areas of Cerebral Cortex • “Executive suite” of the nervous system – home of conscious mind • Enables people to: o Aware of themselves & their sensations o Initiate & control voluntary movements o Communicate, remember & understand • Composed of gray matter – contains neuron cell bodies, dendrites & very short un myelinated axons but no fiber tracts o Many gyri & sulci triple surface area o Accounts for 40% of total mass of brain • Contains neurons arranged in 6 layers • 3 general functional areas o Sensory areas – conscious awareness of sensation o Association areas – integrate diverse information to enable purposeful action o Motor areas – control voluntary motor functions • Sensory area for each of the major senses – each region called primary sensory cortex • Each has association areas linked to it that process sensory information – sensory association areas • Other association areas receive/integrate input from multiple regions– multimodal association areas • Regions of the cortex that plan & initiate voluntary motor functions – motor areas 1. Sensory information is received by primary sensory cortex & arrival of this information results in awareness of the sensation 2. Information is relayed to sensory association area (unimodal) that gives meaning to sensory input 3. Multimodal association area receive input in parallel from multiple sensory association areas – integrate all of sensory input to create complete understanding of sensory information – regions also integrate past experiences & develop a motor response 4. Motor plan is enacted by motor cortex Example: 1. Primary sensory cortex enables you to hear the horn 2. Auditory association cortex indicates horn is a fire alarm 3. Multimodal association area integrate sound with past experience & with other sensory information – areas develop a motor response 4. Motor cortex initiates the movement necessary to enact the motor plan Sensory Areas • Occur in parts of parietal, temporal & occipital lobes • Distinct cortical area: primary sensory cortex for each of the major senses o General somatic senses o Special senses of vision, hearing, balance, olfaction & taste • Primary sensory cortex - aware of sensory stimuli • Sensory association areas adjacent to primary sensory area interpret sensory stimulus & gives meaning to sensation 1. Somatosensory Areas: • Primary somatosensory cortex o Receives information from general somatic senses (touch, pressure, vibration, pain & temperature from the skin & proprioception from muscles & joints) o Enables conscious awareness of sensations o Located along postcentral gyrus of parietal lobe o General somatic sensations are picked up by sensory receptors in periphery of body & relayed through the spinal cord, brain stem & thalamus to primary somatosensory cortex o Cortical neurons process information & identify precise area of the body being stimulated o Each region receives sensory stimuli from a specific area of the body o Sensory input from body can be mapped onto postcentral gyrus o Map of the primary sensory cortex: sensory homunculus  Representation is upside down – face on inferolateral part of postcentral gyrus & toes at superomedial  Amount of somatosensory cortex devoted to body region is related to sensitivity of that region – to the number of its sensory receptors  Lips & finger tips = most sensitive o Exhibits contralateral projection from the sensory receptors to the sensory cortex  Right cerebral hemisphere receives its sensory input from the left side of the body  Left cerebral hemisphere receives its sensory input from the right side of the body o Damage destroys conscious ability to feel & localize touch, pressure & vibrations on the skin • Somatosensory Association Cortex o Lies posterior to the primary somatosensory cortex o Integrates sensory inputs (touch, pressure & others) into comprehensive understanding 2. Visual Areas • Primary visual cortex o Posterior and medial part of occipital lobe – much of it buried within deep calcarine sulcus o Largest of all cortical sensory areas – receives visual information that originates from retina o Exhibits contralateral projection  Right half of visual space is represented on the left visual cortex  Left half of visual space is represented on the right visual cortex o Processing here is at comparatively low level – orientation of objects & merging sensory stimuli from both eyes o Damage – person has no conscious awareness of what is being viewed – functionally blind • Visual association area o Surrounds primary visual cortex o Covers much of the occipital lobe o Continues processing visual information by analyzing colour, form & movement 3. Auditory Areas • Primary auditory cortex o Conscious awareness of sound o Located on superior edge of temporal lobe, primarily inside the lateral sulcus o When sound waves excite sound receptors of the inner ear, impulses are transmitted here – in formation is related to loudness, rhythm & pitch • Auditory association area o Lies just posterior & lateral to the primary auditory area o Evaluation of sound: ex. talking, screech, thunder or music 4. Vestibular (equilibrium) cortex • Conscious awareness of sense of balance • Position of the head in space • Located in the posterior part of the insula – deep to the lateral sulcus 5. Gustatory cortex • Conscious awareness of taste stimuli • Lies in insula 6. Ol
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