01 The Cerebral Surface.pdf

The Cerebral Surface Prof Dara M Cannon LOBES & SKULL BONES • Note the difference in size of the corresponding lobe and bone of the same name parietal frontal parietal temporal occipital occipital temporal frontal parietal frontal ethmoid temporal sphenoid occipital Ethmoid: olfactory n...

The Cerebral Surface Prof Dara M Cannon LOBES & SKULL BONES • Note the difference in size of the corresponding lobe and bone of the same name parietal frontal parietal temporal occipital occipital temporal frontal parietal frontal ethmoid temporal sphenoid occipital Ethmoid: olfactory nerves | cribriform plate. Sphenoid: pituitary gland | diaphragm sella – meningeal dural fold. Demo in context rotate ethmoid and sphenoid in ‘3D4Medical’ FOUR MAJOR PARTS OF THE BRAIN ▪ The cerebrum is the newest (evolutionarily) and largest part of the brain as a whole ▪ Contains an outer surface or cortex and deeper grey matter areas termed subcortical nuclei ▪ The diencephalon: thalamus & hypothalamus, some of the subcortical nuclei of the brain ▪ The brain stem is the continuation of the spinal cord and consists of the medulla oblongata, pons and midbrain. ▪ The cerebellum is the second largest part of the brain. I THE CEREBRUM • The cerebral cortex is the “seat of our intelligence”– it’s because of neurons in the cortex that we are able to read, write, speak, remember, and plan our life. • The cerebrum consists of an outer cerebral cortex, an internal region of cerebral white matter, and gray matter nuclei deep within the white matter termed sub-cortical nuclei GREY MATTER & WHITE MATTER Gray matter (gray because it lacks myelin) of the brain and spinal cord is formed from neuronal cell bodies and dendrites. Groups of cell bodies are termed nuclei. White matter of the brain and spinal cord is formed from aggregations of myelinated axons from many neurons. The lipid part of myelin imparts the white appearance. GREY MATTER SHAPE: GYRI & SULCI • During embryonic development, the grey matter of the brain develops faster than the white matter - the cortical region rolls and folds on itself. Convolutions and grooves are created in the cortex during this growth process due to mechanical forces between the cranium and growing brain • The folds are called gyri, the deepest grooves between gyri are known as fissures; the shallower grooves between folds are termed sulci The Cerebral Cortex • Cell layers and regional classification of the cerebral cortex • Neocortex – 6 layers • Composition varies with specialization: sensory or motor LAYER NAME CONNECTIONS I Molecular Dendrites and axons from other layers II External granular Cortical-cortical III External pyramidal Cortical-cortical IV Internal granular Receives from thalamus V Internal pyramidal Sends to subcortex (except thalamus) VI Multiform Sends to thalamus Learning Objectives • Be able to identify, name and describe the main connections the major gyri and sulci of the human cerebrum LATERAL VIEW F1 superior frontal gyrus F2 middle frontal gyrus F3 inferior frontal gyrus p precentral gyrus Po postcentral gyrus T1 superior temporal gyrus T2 middle temporal gyrus T3 inferior temporal gyrus SM supramarginal gyrus A angular gyrus SPL superior parietal lobule O2 middle occipital gyrus O3 inferior occipital gyrus I LATERAL VIEW – opening up the lateral fissure • F3: or – pars orbitalis / tr – pars triangularis / op – pars opercularis • PP – planum polare / polar plane • H – Heschl’s Gyrus I • PT – planum temporalis / temporal plane • as, ms, ps – anterior, middle, posterior short insular gyri • al – anterior long gyrus of the insula (pl not visible) Inferior surface frontal lobe, superior surface or place temporal lobe | later relate to MCA path | locate Heschls in sagittal T1 | primary auditory cortex | Weirnecke’s & Broca’s MEDIAL VIEW 1 superior frontal gyrus d superior most tip of central sulcus 13 lateral occipitotemporal gyrus (LOTG) E entorhinal cortex fo fornix 14 parahippocampal G genu, B body and Sp splenium of the gyrus corpus callosum 21 gyrus rectus k parieto-occipital 22 subcallosal area sulcus 30 cingulate gyrus I calcarine sulcus 31 isthmus of the cingulate gyrus m anterior calcarine sulcus 32 paracentral lobule n subparietal sulcus 33 superior parietal o cingulate sulcus lobule pC precentral sulcus 34 cuneus pM pars marginalis 35 medial sr superior & ir occipitotemporal inferior rostral sulci gyrus (MOTG ) t rhinal sulcus Th thalamus u collateral sulcus z pericallosal sulcus I INFERIOR VIEW Note the temporal poles are cut away revealing structures superior to the sylvian fissure G/GR Gyrus Rectus A/L/M/P anterior, lateral, medial and posterior (O) orbital gyri I PM/PMO posteromedial orbital gyrus MG frontomarginal gyrus I olfactory tract ap apex of the insula Lateral to medial: INFERIOR VIEW T3 inferior temporal gyrus O3 inferior occipital gyrus S occipitotemporal sulcus T4-O4 fusiform gyrus / LOTG (lateral occipitotemporal gyrus) u collateral sulcus t rhinal sulcus T5 parahippocampal gyrus O5 lingula gyrus / MOTG (medial occipitotemporal gyrus) m anterior calcarine sulcus Sp splenium of the corpus callosum Mid midbrain I Superior GYRI 1 superior frontal gyrus 2 middle frontal gyrus 4 precentral gyrus 5 postcentral gyrus 6 & 7 inferior parietal lobule 8 superior parietal lobule 15 superior occipital gyrus SULCI a superior frontal sulcus c precentral sulcus d central sulcus e postcentral sulcus f intraparietal sulcus g intraoccipital sulcus k parieto-occipital sulcus *Thinner postcentral* Primary Sensory & Motor Areas Summary SURFACE ANATOMY OF THE CEREBRUM – KEYNOTES  The undulating cerebral surface presents about one-third of the cortex or cortical grey matter to the viewer and protected and packed within the sulci exists two-thirds more cortex. Here you will learn the gyri and sulci of the cerebrum on gross anatomical and MRI images. Gyral and sulcal patterns vary from person to person thus general principles are applied to determine nomenclature. Generally variation is estimated at about 10% anteriorly growing to up to 50% posteriorly.   Cortex is far from homogenous across the brain: Please note that deep to these cortical regions lie connecting white matter tracts that run to other regions working as a network. Vessels tend to run in the sulci and supply half the adjacent cortical gyri (note adjacent half-gyri sign on imaging). The phylogeny and phyogenetics of the cerebral cortex divides these regions into paleo- (the oldest), archi- (intermediate) and neo- (newest) cortical types/regions. These divisions, the receptor architecture, the cytoarchitecture (cell type, density, size and layer location) and the white matter connections leading to/from cortical areas, form the basis for the clinical deficits observed when pathology occurs in a cerebral cortical location. For example, V1 in the occipital cortex represents the primary termination zone of the visual pathway arising as the optic nerve from the retina of the eye. V1 is high in M2-receptors, it is our primary visual cortex and exists either side of the calcarine fissure. Neural Plasticity and Variation: Functions and their associated cortical locations are plastic within a person (can retrain elsewhere) and vary hugely in the population, leading to surgeons using awake cortical mapping to localise and preserve functions that underlie quality of life (we are uniquely human it is argued, for our ability to use our hands and speak, thus aphasia is usually a focus of assessment: have a quick look at the work of neurosurgeon Duffau, France). Therefore, when assigning a function to a particular cortical region we are generalizing and potentially wrong for any given individual. Duffau has stimulated over 500 so called ‘Broca’s Areas’ and detected invariably, that speech is retained by preservation of a region posterior to that defined originally by Broca.   Cerebral Hemispheres o #2 o Linked by commissural fibers o Separated by a deep ‘longitudinal’ fissure o Fold of dura lies in this fissure: ‘falx cerebri’ Major Gyri – Frontal Lobe o PreCentral Gyrus: primary motor cortex o Superior Frontal Gyrus o Middle Frontal Gyrus o Inferior Frontal Gyrus Convoluted surface ▪ Gyri: ridges of brain cortex ▪ Sulci: CSF filled grooves that separate gyri  Major Gyri – Parietal Lobe o PostCentral Gyrus: primary somatosensory cortex (see homunculus map), separated from the PreCentral Gyrus by the Central Sulcus o Superior parietal lobule o Inferior parietal lobule o Supramarginal gyrus: at the end of the lateral fissure o Angular gyrus o Precuneus: medial surface of lobe Cortex o A gray matter mantle that overlies white matter o Subcortical structures are those beneath this white matter (basal nuclei, thalamus ..) Major Sulci/Fissures o Longitudinal: separates the cerebral hemispheres o Lateral / Sylvian: separates frontal and parietal above from temporal below o Central: separates the frontal and parietal lobes  Major Gyri – Occipital Lobe o Separated from parietal lobe by the parietoccipital sulcus (medial surface) o Primary visual cortex (calcarine sulcus) o Cuneus, medial surface Lobes o Frontal o Parietal o Temporal o   Occipital Insula o Cortical region hidden deep within the lateral fissure o Covered by the ‘opercula’: overhanging cortex of the frontal, parietal and temporal lobes  Major Gyri – Temporal Lobe o Inferior to lateral fissure o Superior temporal gyrus: primary auditory cortex o Middle temporal gyrus o Inferior temporal gyrus o Parahippocampal gyrus, medial surface merges into uncus (inferior view) The National Neuroanatomy Competition NUNC 2024 Additional ‘NUNC’ labelled slides are not examinable for module MD224 but are materials encountered by past University of Galway NUNC competitors See more here: https://www.facebook.com/NatNeuroComp/ NUNC: Broadman Areas • These maps are defined by the location of cells types: they are cytoarchitectonic maps • They correspond reasonably well with areas defined functionally and are thus sometimes encountered clinically NUNC: Broadman Areas • Presenting these images without the BA labels, you may be asked to choose from an MCQ five possible answers what Brodmann area is marked in an image