Cerebral cortex: Difference between revisions
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{{otheruses|Cortex}} |
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[[Image:Cerebral Cortex location.jpg|thumb|200px|Location of the cerebral cortex]] |
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[[Image:Cerebral Cortex 10.5mm.jpg|thumb|200px|Slice of the cerebral cortex, ca. 10.5mm wide]] |
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[[Image:NeuronGolgi.png|thumb|250px|Golgi-stained neurons in the somatosensory cortex of the macaque monkey.]] |
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The '''cerebral cortex''' is a structure within the [[vertebrate]] [[brain]] with distinct structural and functional properties. In non-living, preserved brains, the outermost layers of the [[telencephalon|cerebrum]] has a [[grey]] color, hence the name "grey matter". Grey matter is formed by [[neurons]] and their [[myelin|unmyelinated]] fibers while the white matter below the grey matter of the cortex is formed predominantly by myelinated [[axon]]s interconnecting different regions of the [[central nervous system]]. The human cerebral cortex is 2-4 mm (0.08-0.16 inches) thick and plays a central role in many complex brain functions including [[memory]], [[attention]], perceptual [[awareness]], "[[Thought|thinking]]", [[language]] and [[consciousness]]. |
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The surface of the cerebral cortex is [[fold]]ed in large mammals where more than two thirds of the cortical surface is buried in the grooves, called "[[sulcus (neuroanatomy)|sulci]]". The [[phylogeny|phylogenetically]] more ancient part of the cerebral cortex, the [[hippocampus]], is differentiated in [[Brain#Comparative anatomy|five layers of neurons]], while the more recent neo-cortex is differentiated in six basic layers. Relative variations in thickness or cell type (among other parameters) allows us to distinguish among different neocortical architectonic fields. The geometry of these fields seems to be related to the anatomy of the cortical folds and, for example, layers in the upper part of the cortical grooves (called [[gyri]]) are more clearly differentiated than in its deeper parts (called sulcal "fundi"). |
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== Development == |
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The cerebral cortex develops from the [[neural plate]], a specialised part of the embryonic [[germ layer|ectoderm]]. The neural plate folds and closes to form the [[neural tube]]. From the cavity inside the neural tube develops the [[ventricular system]], and, from the epithelial cells of its walls, the neurons and [[glial cells]]. The most-frontal part of the neural tube, the ''[[telencephalon]]'', gives rise to the cerebral hemispheres and the [[neocortex]]. |
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Most cortical neurons are generated within the ventricular zone close to the ventricles. Initially, progenitor cells in the ventricular zone divide symmetrically, producing two progenitor cells by [[Mitosis|mitotic cycle]]. Then, some progenitor cells begin to divide asymmetrically, producing one postmitotic cell that migrates radially and leaves the ventricular zone, and a daughter cell that continues to divide or that eventually dies. |
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The migrating cells will become neurons.<ref>{{Cite journal |
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| author = P. Rakic |
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| year = [[1988]] |
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| title = Specification of cerebral cortical areas |
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| journal = [[Science (journal)|Science]] |
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| volume = 241 |
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| issue = 4862 |
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| pages = 170–176 |
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| doi = 10.1126/science.3291116 |
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| url = http://www.sciencemag.org/cgi/content/abstract/241/4862/170 |
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}}</ref> |
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Recent work has identified [[Radial glia|radial glial cells]] (also [[Glial cells|here]]) as one population of progenitor cells.<ref>{{Cite journal |
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| author = [[Stephen C. Noctor]], Alexander C. Flint, Tamily A. Weissman, Ryan S. Dammerman & [[Arnold R. Kriegstein]] |
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| year = [[2001]] |
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| title = Neurons derived from radial glial cells establish radial units in neocortex |
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| journal = [[Nature (journal)|Nature]] |
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| volume = 409 |
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| issue = 6821 |
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| pages = 714–720 |
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| pmid = 11217860 |
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| doi = 10.1038/35055553 |
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| url = http://www.nature.com/nature/journal/v409/n6821/abs/409714a0.html |
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}}</ref> |
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During fetal and neonatal life, the immature cerebral cortex (the cortical plate) is sandwiched between two synaptic zones: the marginal zone above and an area just below the cortical plate, the subplate. The subplate is transient and disappears by approximately 2 months postnatal (Friauf, 1991). |
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== Laminar pattern == |
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The standard areas of cortex (isocortex) is characterized as having six distinct layers. From outside inward: |
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# Molecular layer |
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# External granular layer |
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# External pyramidal layer |
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# Internal granular layer |
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# Internal pyramidal layer |
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# Multiform layer. |
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After migration, neurons form [[efferent]]s and receive [[afferent]] connections characteristic of their layer. It is interesting to note that during development, the inner layers are formed before the outer layers are. |
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# The molecular layer I contains few scattered neurons and consists mainly of extensions of apical dendrites and horizontally oriented axons, and some [[Cajal-Retzius cell|Cajal-Retzius]] and spiny stellate neurons can be found. |
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# The external granular layer II contains small [[Pyramidal cell|pyramidal neurons]] and numerous stellate neurons. |
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# The external pyramidal layer III contains predominantly small and medium sized [[pyramidal neurons]], as well as non-pyramidal neurons with vertically-oriented intracortical axons. Layers I through III are the main target of interhemispheric corticocortical afferents, and layer III is the principal source of corticocortical efferents. |
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# The internal granular layer IV contains different types of [[stellate cell|stellate]] and [[pyramidal neurons]], and is the main target of thalamocortical afferents as well as intra-hemispheric corticocortical afferents. |
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# The internal pyramidal layer V contains large [[pyramidal neurons]] (as the Betz cells in the primary motor cortex), as well as interneurons, and it is the principal source of efferent for all the motor-related subcortical structures. |
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# The multiform layer VI contains few large [[pyramidal|pyramidal neurons]] and many small spindle-like pyramidal and [[multiform neurons]]. The layer VI sends efferent fibers to the thalamus establishing a very precise reciprocal interconnection between the cortex and the thalamus (Creutzfeldt, 1995). |
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During early development, there is an additional layer of neurons present in the future white matter. these are called [[subplate]] neurons and these neurons disappear during postnatal development. |
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The cortical layers are not simply stacked one over the other; they develop characteristic connections between different layers, which define the basic structure of the [[cortical column]]s in the mature cortex (Mountcastle, 1997). |
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There are no actual borders between the layers, and [[neurons]] cross layer boundaries with their dendrites and axons trees all over. The [[pyramidal cells]] (the majority of the neurons) span at least three layers, and in many cases all the layers. Thus, it is not obvious that the layers have any functional significance. However, the flow of current in the cortical layers is consistent and shows inputs principally in layer IV, and the spread of activity, and thus the flow of information, roughly follows the models put forth by Martin, Whitteridge, and Somogyi in 1985. |
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==Connections of the cerebral cortex== |
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The cerebral cortex sends connections (efferents) and receives connections (afferents) from many subcortical structures like the [[thalamus]] and [[basal ganglia]]. Most of the sensory stimulation arrives at the cerebral cortex indirectly through different thalamic nuclei. This is the case of touch, vision and sound but not of olfactory stimulation, which passes to the [[olfactory bulb]] and then to the olfactory ([[pyriform]]) cortex. The largest part of the connections arriving at the cerebral cortex do not come from subcortical structures however. The main source of cortical stimulation is the cerebral cortex itself: maybe 99% of the total connections (Braitenberg and Schüz, 1991). |
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Other areas receive impulses from the primary sensory areas and integrate the information coming in from different types of receptors (i.e., modalities). These are often called association areas and make up a great deal of the cortex in all primates, humans included. Thus, the cortex is commonly described as comprised of the primary sensory areas, the motor areas and the association area. |
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===Motor areas=== |
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The motor areas are located in both hemispheres of the cortex. They are shaped like a pair of headphones stretching from ear to ear. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of your body and vice versa. |
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Two areas of the cortex are commonly referred to as motor: |
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* ''[[Primary motor cortex]]'', which '''executes''' voluntary movements |
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* ''Supplementary motor areas'' and ''premotor cortex'', which '''select''' voluntary movements. |
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In addition, motor functions have been described for: |
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* ''Posterior Parietal Cortex'', which guides voluntary movements in space |
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* ''Dorsolateral Prefrontal Cortex'', which decides which voluntary movements to make according to higher-order instructions, rules, and self-generated thoughts. |
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===Sensory areas=== |
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[[Cortical area|Areas]] that receive that particular information are called sensory areas. Parts of the cortex that receive sensory inputs from the [[thalamus]] are called primary sensory areas. The senses of vision, audition and touch are served by the primary [[visual cortex]], primary [[auditory cortex]] and primary [[somatosensory cortex]]. In general, the two hemispheres receive the information from the opposite sides of the [[body]]. For example the right primary somatosensory cortex receives information from the left limbs and the right visual cortex receives information from the left visual field. The organisation of sensory maps in the cortex reflects that of the corresponding sensing organ, in which is known as a [[Topographic map (Neuroanatomy)|topographic map]]. Neighbouring points in the primary [[visual cortex]], for example, correspond to neighbouring points in the [[retina]]. This [[Topographic map (Neuroanatomy)|topographic map]] is called a [[retinotopy|retinotopic map]]. In the same way, there exists a [[tonotopy|tonotopic map]] in the primary auditory cortex and a [[somatotopy|somatotopic map]] in the primary sensory cortex. This last topographic map of the body onto the Posterior Central Gyrus has been illustrated as deformed human representation, the somatosensory [[homunculus]], where the size of different limbs reflects the importance of their innervation. |
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===Association areas=== |
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Association areas comprise three major groups: |
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# [[parietal lobe|Parietal]], [[Temporal lobe|temporal]], and [[occipital lobe]]s - all located in the posterior part of the brain - are involved in producing our perceptions resulting from what our eyes see, ears hear, and other sensory organs inform us about the position of different parts of our body and relate them to the position of other objects in the environment |
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# [[Frontal lobe]] - called ''prefrontal association complex'' and involved in planning actions and movement, as well as abstract thought |
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In humans, the association areas of the left hemisphere, especially the parietal-temporal-occipital complex, are responsible for our understanding and use of language. |
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== Classification == |
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Based on the differences in lamination the cerebral cortex can be classified into two major groups: |
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* [[Isocortex]] (homotypical cortex), the part of the cortex with six layers. |
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* [[Allocortex]] (heterotypical cortex) with variable number of layers, e.g., [[olfactory cortex]] and [[hippocampus]]. |
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Auxiliary classes are: |
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* [[Mesocortex]], classification between isocortex and allocortex where layers 2, 3 and 4 are merged. |
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* [[Proisocortex]], [[Brodmann area]]s [[Brodmann area 24|24]], [[Brodmann area 25|25]], [[Brodmann area 32|32]]. |
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* [[Periallocortex]] is cortical areas adjacent to [[allocortex]]. |
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Based on supposed developmental differences the following classification also appears: |
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* [[Neocortex]] or [[Neopallium]] that corresponds to the isocortex. |
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* [[Archicortex]] |
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* [[Paleocortex]] |
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In addition, cortex may be classified on the basis of gross topographical conventions into the following: |
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* Temporal Cortex |
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* Parietal Cortex |
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* Frontal Cortex |
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* Occipital Cortex |
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== Cortical thickness == |
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With magnetic resonance [[brain scanner]]s it is possible to get a measure for the thickness of the human cerebral cortex and relate it to other measures. |
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One study has found some positive association between the cortical thickness and [[intelligence]].<ref>{{Cite journal |
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| author = Katherine L. Narr, [[Roger P. Woods]], [[Paul M. Thompson]], Philip Szeszko, Delbert Robinson, Teodora Dimtcheva, Mala Gurbani, [[Arthur W. Toga]] and Robert M. Bilder |
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| title = Relationships between IQ and Regional Cortical Gray Matter Thickness in Healthy Adults |
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| journal = [[Cerebral Cortex (journal)|Cerebral Cortex]] |
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| volume = 17 |
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| issue = 9 |
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| pages = 2163–2171 |
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| year = 2007 |
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| url = http://cercor.oxfordjournals.org/cgi/content/abstract/17/9/2163 |
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}}</ref> |
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== See also == |
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* [[Cortical column]] |
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* [[Frontal lobe]] |
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* [[Limbic system]] |
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* [[List of regions in the human brain]] |
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* [[Microgyrus]] |
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* [[Occipital lobe]] |
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* [[Parietal lobe]] |
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* [[Temporal lobe]] |
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* [[Cerebral hemisphere]] |
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* [[Subplate]] |
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* [[Brain-computer interface]] |
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==Further reading== |
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* Kandel, E.R., Schwartz, J. H., and Jessell, T.M. ''Principles of Neural Science'' (Fourth Edition). 2000. New York, McGraw Hill. ISBN 0-8385-7701-6. |
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* Zigmond, M. J., Bloom, F. E., Landis, S.C., Roberts, J.L, and Squire, L.R. ''Fundamental Neuroscience''. 1999. San Diego, Academic Press. ISBN 0-12-780870-1. |
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==References== |
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<div class="references-small"><references/></div> |
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* Angevine, J. and Sidman, R. 1961. Autoradiographic study of cell migration during histogenesis of cerebral cortex in the mouse. ''Nature'', 192:766-768 |
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* Creuzfeldt, O. 1995. ''Cortex Cerebri''. Springer-Verlag. |
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* Marin-Padilla, M. 2001. Evolución de la estructura de la neocorteza del mamífero: Nueva teoría citoarquitectónica. ''Rev. Neurol'', 33(9):843-853 |
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* Mountcastle, V. 1997. The columnar organization of the neocortex. ''Brain'', 120:701-722 |
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* Noctor SC, Flint AC, Weissman TA, Dammerman RS, Kriegstein AR. (2001) Neurons derived from radial glial cells establish radial units in neocortex. "Nature" 409(6821):714-720. PMID 11217860 |
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* Ogawa, M. ''et al.'' 1995. The reeler gene-associated antigen on Cajal-Retzius neurons is a crucial molecule for laminar organization of cortical neurones. ''Neuron'', 14:899-912 |
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* Rakic, P. 1988. Specification of cerebral cortical areas. ''Science'', 241:170-176 |
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* Friauf, J. 1991. Changing patterns of synaptic input to subplate and cortical plate during development of visual cortex. |
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* Braitenberg, V and Schüz, A 1991. "Anatomy of the Cortex: Statistics and Geometry" NY: Springer-Verlag |
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== External links == |
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* {{BrainInfo|hier|20}} |
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* {{BrainMaps|cerebral%20cortex|cerebral cortex}} |
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* [http://webvision.med.utah.edu/VisualCortex.html Webvision - The primary visual cortex] Comprehensive article about the structure and function of the primary visual cortex. |
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* [http://webvision.med.utah.edu/imageswv/BasicCells.jpg Webvision - Basic cell types] Image of the basic cell types of the monkey cerebral cortex. |
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*[http://info.med.yale.edu/chldstdy/plomdevelop/development/Arch1.html Development of the Cerebral Cortex] Different topics on cortical development in the form of columns written by leading scientists. |
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{{Prosencephalon}} |
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[[Category:Cerebrum]] |
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[[Category:Neuroanatomy]] |
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[[da:Hjernebark]] |
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[[de:Großhirnrinde]] |
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[[es:Corteza cerebral]] |
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[[fr:Cortex cérébral]] |
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[[he:קליפת המוח]] |
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[[nl:Cerebrale cortex]] |
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[[ja:大脳皮質]] |
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[[pl:Kora mózgu]] |
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[[pt:Córtex cerebral]] |
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[[fi:Aivokuori]] |
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[[sv:Hjärnbark]] |
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[[yi:קאָרטעקס]] |
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[[zh:大脑皮质]] |
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Revision as of 16:12, 28 September 2007
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