BMS2-20 Brain Hemispheres and Medullary Substance PDF

• Telencephalon Cerebrum • Largest part of the brain • Containing the cerebral cortex (of the 2 cerebral hemispheres), several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb • Is the uppermost region of the central nervous system Cerebrum • Located superiorl...

• Telencephalon Cerebrum • Largest part of the brain • Containing the cerebral cortex (of the 2 cerebral hemispheres), several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb • Is the uppermost region of the central nervous system Cerebrum • Located superiorly & anteriorly vs. brainstem • In bony cranium • 2 lobes; R& L separated by the falx cerebri of the dura mater • Fills anterior & middle cranial fossae • Extends from frontal bone to occipital bone Cerebral Cortex • Sulci: Grooves/depressions (singular sulcus) • Gyri (singular: gyrus) : Ridges/elevations • Fissure: A very deep sulcus Cerebral Cortex • Longitudinal fissure: Divides cerebrum into 2 anatomically symmetrical hemispheres Is a major sulcus that runs in the median sagittal plane • Falx cerebri (a fold of dura mater) descends vertically to fill the longitudinal fissure Cerebrum Longitudinal fissure Cerebrum Transverse fissure Cerebrum Transverse fissure Cerebrum • Grey matter: • Forms surface of each cerebral hemisphere (known as the cerebral cortex) • Associated w/ processing & cognition • White matter: • Forms bulk of deeper parts • Glial cells & myelinated axons that connect various grey matter areas Cerebrum – The Lobes • Frontal • Temporal • Parietal • Occipital • Insular (insula) • ---- Limbic ----- Cerebrum – The Lobes • Classified into 4 lobes, according to name of app. corresponding cranial bone • Each contains various cortical association areas • Together, these areas function for perceptual interpretation & experience of surrounding environment Cerebrum – The Lobes Frontal Lobe • Beneath the frontal bone • Most anterior region of cerebrum • Separated from parietal lobe posteriorly by central sulcus & from temporal lobe inferoposteriorly by lateral sulcus Cerebrum – The Lobes Parietal lobe • Below parietal bone, btwn frontal lobe anteriorly & occipital lobe posteriorly • Separated from frontal lobe by the central sulcus • Separated from occipital lobe by the parieto-occipital sulcus • Superior to temporal lobe & separated by the lateral sulcus Cerebrum – The Lobes Occipital Lobe • Most posterior part of cerebrum • Below occipital bone • Rests upon tentorium cerebelli which separates cerebrum from cerebellum • Separated from occipital, parietal & temporal lobes anteriorly by the parieto-occipital sulcus Cerebrum – The Lobes Temporal lobe • Beneath temporal bone • Inferior to frontal & parietal lobes, from which it is separated by the lateral sulcus Cerebrum – The Lobes • . Cerebrum – The Lobes • . Cerebrum – The Lobes Insula • Area of cerebral cortex not usually included in decscriptions of lobes • Buried in depths of the lateral sulcus • Concealed from view by portions of frotal, parietal & temporal lobes • Operculum: Portion of lobes overlying the insula • Latin: Lid Cerebrum – The Lobes Operculum Insula • Latin: "little lid« • Frontal, temporal, parietal operculum • Together cover the insula as the opercula of insula Cerebrum Sulci & Gyri Cerebrum Main Sulci: • Central s – groove separating frontal & parietal lobes • Lateral s – groove separating frontal & parietal lobes from temporal lobe • Lunate s – groove located in occipital cortex Cerebrum Main Gyri: • Precentral g – ridge directly ant. to central sulcus, location of primary motor cortex • Postcentral g – ridge directly post. to central sulcus, location of primary somatosensory cortex • Superior temporal gyrus – ridge located inf. to lateral sulcus, responsible for reception and processing of sound Cerebrum Gyri & Sulci Cerebral Cortex . - Functions Cerebral Cortex . - Functions Cerebral Cortex Brodman Areas • 52 functional areas mapped & classified - Functions Cerebral Cortex . - Functions Cerebral Cortex . - Functions • Homunculus (L: Little man) Motor Homunculus • Representation of body based on neurological "map" of areas & proportions of cortex dedicated to processing motor functions • Contains considerable overlap • A single neuron in primary motor cortex can influence activity of many muscles related to many joints • Primary motor cortex (Brodmann area 4) frontal lobe, precentral gyrus Cortex – Sensory Homunculus • Representation of body based on neurological "map" of areas & proportions of cortex dedicated to processing sensory functions • Primary sensory cortex located in postcentral gyrus in lateral parietal lobe • Processes signals coming from thalamus Cortex – Homunculus . Cortical Areas FRONTAL LOBE • Brodman 4 : Primary motor cortex Precentral gyrus • Brodman 6: Premotor cortex & supplementary motor area Ant to 4 Planning of complex, coordinated movements Damage: apraxia • Brodman 8: Frontal eye fields – resp for saccadic smooth pursuit eye movements Ant & inf to 6 Contralateral horizontal gaze • Brodman 44, 45: Broca’s motor speech area. Semantic tasks. Inferior frontal gyrus • Prefrontal cortex: Executive function Cortical Areas PARIETAL LOBE • Brodman 3, 1, 2 : Primary somatosensory cortex Postcentral gyrus • Brodman 5: Posterior Parietal Association cortex Integrates tactile w/proprioceptive • Brodman 7: Posterior Parietal Association cortex Integrates tactile w/visual & proprioceptive - stereognostic & visual info • Brodman 39: Convergence of auditory, visual & somatosensory info Angular gyrus • Brodman 40: Convergence of auditory, visual & somatosensory info Supramarginal gyrus Sensory initiation & guidance of movement Cortical Areas OCCIPITAL LOBE Visual cortex on en either side of calcarine sulcus, medial portion of occipital lobe : • Brodman 17: Primary visual cortex Striate area • Brodman 18: Parastriate area – Visual Association Area Interpretation of images • Brodman 19: Peristriate or extrastriate area – Visual Association Area Bounded by parietoocciptal sulcus Macula represented in most post. part of occipital lobe Blows to back of head or blockage to branches of middle cerebral a. may cause loss of macular representationof visual fields Cortical Areas TEMPORAL LOBE • Brodman 41, 42: Primary auditory cortex Sup & lateral aspect of temporal lobe Transverse temporal gyri of Heschl • Brodman 22: Wernicke area. In L- dominant hemisphere Auditory association area Language comprehension Surrounded by auditory cortex Lesion: Receptive (fluent/sensory) aphasia May also incl areas 39 & 40 in parietal lobe • Brodman 34: Olfactory cortex In uncus Part of the entorhinal area & superior temporal gyrus Cortical Areas • Brodman 43: Gustatory center Occupies postcentral gyrus Anterior insula - front operculum White Matter Substantia medullaris telencephali Myelinated Axons Commisural fibers • Opposite hemisphere Association fibers • Same hemisphere Projection Fibers • Lower areas Projection Fibers • Internal Capsule • Corona Radiata • Afferent & efferent tracts between cortex & periphery • Cerebal peduncles, pyramids • Form a continuous fiber system from cerebral cortex down to spinal cord Projection Fibers Corona Radiata • Fan-shaped mass of white matter (fibers) • Continues ventrally as the internal capsule • Continues dorsally as the centrum semiovale • This sheet of ascending & descending axons carries most of neural traffic from & to cerebral cortex • Corona radiata is associated w/ corticopontine tract, corticobulbar tract & corticospinal tract Projection Fibers . Projection Fibers Internal Capsule • Comprised of all fibers that go to & come from cerebral cortex • Fibers within connect thalamus w/ cerebral cortex by thalamocortical & corticothalamic fibers • In addition also contains axons which descend from cortex to lower levels of neuraxis such as brain stem & spinal cord • These efferent fiber systems - referred to as corticofugal fibers - include the corticoreticular, corticopontine, corticobulbar & cortico spinal tracts • Smaller projections also exist to basal ganglia, other areas of the diencephalon & midbrain Projection Fibers Internal Capsule • 3 parts • Parts best appreciated in transverse sections • Anterior limb: btwn the lenticular nucleus (comprised of putamen & globus pallidus) & head of caudate nucleus • Posterior Limb btwn lenticular nucleus & thalamus • Genu (or knee) : Portion btwn anterior & posterior limbs & is closest to midline. Commisural Fibers Corpus Callosum • L: "tough body" • Wide, thick tract, flat bundle of commissural fibers, beneath cortex • Connects L & R cerebral hemispheres • Spans part of longitudinal fissure • Forms part of roof of lateral ventricles • Callosal sulcus separates it from cingulate gyrus • A number of separate nerve tracts within it, classed as sub-regions • Main ones: The genu, the rostrum, the trunk or body & the splenium • Connect different parts of hemispheres Corpus Callosum Genu: Commisural Fibers Front part, curves downward & backward Rostrum (L: Bird’s beak) Lower much thinner part Splenium (L: Bandage): • End part, towards cerebellum Trunk (Body) • Btwn splenium & genu Commisural Fibers Corpus Callosum Commisural Fibers Corpus Callosum Commisural Fibers Corpus Callosum Fiber tracts from 6 segments of corpus callosum providing interhemispheric linkage btwn specific cortical regions. Genu (coral), premotor (green), sensory-motor (purple), parietal (pink), temporal (yellow), and splenium (blue). Commisural Fibers Anterior Commisure • White matter tract connecting the 2 temporal lobes • Majority of fibers travel thru corpus callosum Commisural Fibers Anterior Commisure Commisural Fibers Posterior Commisure • A.ka. epithalamic commissure • Rounded band of axons crossing mid-line on dorsal aspect of rostral end of the cerebral aqueduct • Interconnects the pretectal nuclei, mediating the consensual pupillary light reflex • Is the inferior lamina (stalk) of the pineal gland that attaches it to posterior wall of 3rd ventricle. Projection Fibers • Afferent & efferent fibers between cortex & lower levels • Below level of thalamus, corticofugal fiber systems (fibers that move away from cortex) make up the Cerebral Peduncle of the midbrain (a.k.a. crus cerebri) • In the brainstem, these fibers make up the Pyramids