Brodmann area 4
Brodmann area 4 refers to the primary motor cortex of the human brain. It is located in the posterior portion of the frontal lobe. Brodmann area 4 is part of the precentral gyrus; the borders of this area are: the precentral sulcus in front, the medial longitudinal fissure at the top, the central sulcus in back, the lateral sulcus along the bottom. This area of cortex, as shown by Wilder Penfield and others, has the pattern of a homunculus; that is, the legs and trunk fold over the midline. Because Brodmann area 4 is in the same general location as primary motor cortex, the homunculus here is called the motor homunculus; the term area 4 of Brodmann-1909 refers to a cytoarchitecturally defined portion of the frontal lobe of the guenon. It is located predominantly in the precentral gyrus. Brodmann-1909 regarded it as topographically and cytoarchitecturally homologous to the human gigantopyramidal area 4 and noted that it occupies a much greater fraction of the frontal lobe in the monkey than in the human.
Distinctive features: the cortex is unusually thick. Brodmann area List of regions in the human brain List of Brodmann areas
The olfactory system, or sense of smell, is the part of the sensory system used for smelling. Most mammals and reptiles have an accessory olfactory system; the main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli. The senses of smell and taste are referred to together as the chemosensory system, because they both give the brain information about the chemical composition of objects through a process called transduction; the peripheral olfactory system consists of the nostrils, ethmoid bone, nasal cavity, the olfactory epithelium. The primary components of the layers of epithelial tissue are the mucous membranes, olfactory glands, olfactory neurons, nerve fibers of the olfactory nerves. Odor molecules can enter the peripheral pathway and reach the nasal cavity either through the nostrils when inhaling or through the throat when the tongue pushes air to the back of the nasal cavity while chewing or swallowing. Inside the nasal cavity, mucus lining the walls of the cavity dissolves odor molecules.
Mucus covers the olfactory epithelium, which contains mucous membranes that produce and store mucus and olfactory glands that secrete metabolic enzymes found in the mucus. Transduction Olfactory sensory neurons in the epithelium detect odor molecules dissolved in the mucus and transmit information about the odor to the brain in a process called sensory transduction. Olfactory neurons have cilia containing Olfactory receptors that bind to odor molecules, causing an electrical response that spreads through the Sensory neuron to the olfactory nerve fibers at the back of the nasal cavity. Olfactory nerves and fibers transmit information about odors from the peripheral olfactory system to the central olfactory system of the brain, separated from the epithelium by the cribriform plate of the ethmoid bone. Olfactory nerve fibers, which originate in the epithelium, pass through the cribriform plate, connecting the epithelium to the brain's limbic system at the olfactory bulbs; the main olfactory bulb transmits pulses to both mitral and tufted cells, which help determine odor concentration based off the time certain neuron clusters fire.
These cells note differences between similar odors and use that data to aid in recognition. The cells are different with mitral having low firing-rates and being inhibited by neighboring cells, while tufted have high rates of firing and are more difficult to inhibit; the uncus houses the olfactory cortex which includes the piriform cortex, olfactory tubercle, parahippocampal gyrus. The olfactory tubercle connects to numerous areas of the amygdala, hypothalamus, brain stem, auditory cortex, olfactory system. *In total it has 27 inputs and 20 outputs. An oversimplification of its role is to state that it: checks to ensure odor signals arose from actual odors rather than villi irritation, regulates motor behavior brought on by odors, integrates auditory and olfactory sensory info to complete the aforementioned tasks, plays a role in transmitting positive signals to reward sensors; the amygdala processes pheromone and kairomone signals. Due to cerebrum evolution this processing is secondary and therefore is unnoticed in human interactions.
Allomones include flower scents, natural herbicides, natural toxic plant chemicals. The info for these processes comes from the vomeronasal organ indirectly via the olfactory bulb; the main olfactory bulb's pulses in the amygdala are used to pair odors to names and recognize odor to odor differences. Stria terminalis bed nuclei, act as the information pathway between the amygdala and hypothalamus, as well as the hypothalamus and pituitary gland. BNST abnormalities lead to sexual confusion and immaturity. BNST connects to the septal area, rewarding sexual behavior. Mitral pulses to the hypothalamus promote/discourage feeding, whereas accessory olfactory bulb pulses regulate reproductive and odor-related-reflex processes; the hippocampus receives all of its olfactory information via the amygdala. The hippocampus forms reinforces existing memories; the parahippocampus encodes and contextualizes scenes. The parahippocampal gyrus houses the topographical map for olfaction; the orbitofrontal cortex is correlated with the cingulate gyrus and septal area to act out positive/negative reinforcement.
The OFC is the expectation of reward/punishment in response to stimuli. The OFC represents the reward in decision making; the anterior olfactory nucleus distributes reciprocal signals between the olfactory bulb and piriform cortex. The anterior olfactory nucleus is the memory hub for smell. Loss of smell is known as anosmia. Anosmia can occur on a single side. Olfactory problems can be divided into different types based on their malfunction; the olfactory dysfunction can be total, distorted, or can be characterized by spontaneous sensations like phantosmia. An inability to recognize odors despite a functioning olfactory system is termed olfactory agnosia. Hyperosmia is a rare condition. Like vision and hearing, the o
The piriform cortex, or pyriform cortex, is a region in the brain, part of the rhinencephalon situated in the cerebrum. The function of the piriform cortex relates to the sense of smell; the piriform cortex is part of the rhinencephalon situated in the cerebrum. In human anatomy, the piriform cortex has been described as consisting of the cortical amygdala and anterior parahippocampal gyrus. More the human piriform cortex is located between the insula and the temporal lobe and laterally of the amygdala; the function of the piriform cortex relates to olfaction, the perception of smell. This has been shown in humans for the posterior piriform cortex; the piriform cortex in rodents and some primates has been shown to harbor cells expressing markers of plasticity such as doublecortin and PSA-NCAM which are modulated by the noradrenergic neurotransmitter system. Sometimes called the olfactory cortex, olfactory lobe or paleopallium, piriform cortical regions are present in the brains of amphibians and mammals.
The piriform cortex is among three areas that emerge in the telencephalon of amphibians, situated caudally to a dorsal area, caudal to a hippocampal area. Further along the phylogenic timeline, the telencephalic bulb of reptiles as viewed in a cross section of the transverse plane extends with the archipallial hippocampus folding toward the midline and down as the dorsal area begins to form a recognizable cortex; as mammalian cerebrums developed, volume of the dorsal cortex increased in greater proportion, as compared proportionally with increased overall brain volume, until it enveloped the hippocampal regions. Recognized as neopallium or neocortex, enlarged dorsal areas envelop the paleopallial piriform cortex in humans and Old World monkeys. Among taxonomic groupings of mammals, the piriform cortex and the olfactory bulb become proportionally smaller in the brains of phylogenically younger species; the piriform cortex occupies a greater proportion of the overall brain and of the telencephalic brains of insectivores than in primates.
The piriform cortex continues to occupy a consistent albeit small and declining proportion of the large telencephalon in the most recent primate species while the volume of the olfactory bulb becomes less in proportion. The piriform cortex contains a critical, functionally defined epileptogenic trigger zone, "Area Tempestas". From this site in piriform cortex chemical and electrically evoked seizures can be triggered, it is the site of action for the proconvulsant action of chemoconvulsants. Regions in the human brain hier-147 at NeuroNames Diagram High Resolution Images of Piriform Cortex
In biology, phylogenetics is the study of the evolutionary history and relationships among individuals or groups of organisms. These relationships are discovered through phylogenetic inference methods that evaluate observed heritable traits, such as DNA sequences or morphology under a model of evolution of these traits; the result of these analyses is a phylogeny – a diagrammatic hypothesis about the history of the evolutionary relationships of a group of organisms. The tips of a phylogenetic tree can be living organisms or fossils, represent the "end", or the present, in an evolutionary lineage. Phylogenetic analyses have become central to understanding biodiversity, evolution and genomes. Taxonomy is the identification and classification of organisms, it is richly informed by phylogenetics, but remains a methodologically and logically distinct discipline. The degree to which taxonomies depend on phylogenies differs depending on the school of taxonomy: phenetics ignores phylogeny altogether, trying to represent the similarity between organisms instead.
Usual methods of phylogenetic inference involve computational approaches implementing the optimality criteria and methods of parsimony, maximum likelihood, MCMC-based Bayesian inference. All these depend upon an implicit or explicit mathematical model describing the evolution of characters observed. Phenetics, popular in the mid-20th century but now obsolete, used distance matrix-based methods to construct trees based on overall similarity in morphology or other observable traits, assumed to approximate phylogenetic relationships. Prior to 1950, phylogenetic inferences were presented as narrative scenarios; such methods are ambiguous and lack explicit criteria for evaluating alternative hypotheses. The term "phylogeny" derives from the German Phylogenie, introduced by Haeckel in 1866, the Darwinian approach to classification became known as the "phyletic" approach. During the late 19th century, Ernst Haeckel's recapitulation theory, or "biogenetic fundamental law", was accepted, it was expressed as "ontogeny recapitulates phylogeny", i.e. the development of a single organism during its lifetime, from germ to adult, successively mirrors the adult stages of successive ancestors of the species to which it belongs.
But this theory has long been rejected. Instead, ontogeny evolves – the phylogenetic history of a species cannot be read directly from its ontogeny, as Haeckel thought would be possible, but characters from ontogeny can be used as data for phylogenetic analyses. 14th century, lex parsimoniae, William of Ockam, English philosopher and Franciscan friar, but the idea goes back to Aristotle, precursor concept 1763, Bayesian probability, Rev. Thomas Bayes, precursor concept 18th century, Pierre Simon first to use ML, precursor concept 1809, evolutionary theory, Philosophie Zoologique, Jean-Baptiste de Lamarck, precursor concept, foreshadowed in the 17th century and 18th century by Voltaire and Leibniz, with Leibniz proposing evolutionary changes to account for observed gaps suggesting that many species had become extinct, others transformed, different species that share common traits may have at one time been a single race foreshadowed by some early Greek philosophers such as Anaximander in the 6th century BC and the atomists of the 5th century BC, who proposed rudimentary theories of evolution 1837, Darwin's notebooks show an evolutionary tree 1843, distinction between homology and analogy, Richard Owen, precursor concept 1858, Paleontologist Heinrich Georg Bronn published a hypothetical tree to illustrating the paleontological "arrival" of new, similar species following the extinction of an older species.
Bronn did not propose a mechanism responsible for precursor concept. 1858, elaboration of evolutionary theory and Wallace in Origin of Species by Darwin the following year, precursor concept 1866, Ernst Haeckel, first publishes his phylogeny-based evolutionary tree, precursor concept 1893, Dollo's Law of Character State Irreversibility, precursor concept 1912, ML recommended and popularized by Ronald Fisher, precursor concept 1921, Tillyard uses term "phylogenetic" and distinguishes between archaic and specialized characters in his classification system 1940, term "clade" coined by Lucien Cuénot 1949, Jackknife resampling, Maurice Quenouille, precursor concept 1950, Willi Hennig's classic formalization 1952, William Wagner's groundplan divergence method 1953, "cladogenesis" coined 1960, "cladistic" coined by Cain and Harrison 1963, first attempt to use ML for phylogenetics and Cavalli-Sforza 1965 Camin-Sokal parsimony, first parsimony criterion and first computer program/algorithm for cladistic analysis both by Camin and Sokal character compatibility method called clique analysis, introduced independently by Camin and Sokal and E. O. Wilson 1966 English translation of Hennig "cladistics" and "cladogram" coined 1969 dynamic and successive wei
Betz cells are giant pyramidal cells located within the fifth layer of the grey matter in the primary motor cortex. They are named after Ukrainian scientist Vladimir Betz, who described them in his work published in 1874; these neurons are the largest in the central nervous system. Betz cells are upper motor neurons that send their axons down to the spinal cord via the corticospinal tract, where in humans they synapse directly with anterior horn cells, which in turn synapse directly with their target muscles. While Betz cells have one apical dendrite typical of pyramidal neurons, they have more primary dendritic shafts, which can branch out at any point from the soma; these perisomatic and basal dendrites project into all cortical layers, but most of their horizontal branches/arbors populate layers V and VI, some reaching down into the white matter. According to one study, Betz cells represent about 10% of the total pyramidal cell population in layer Vb of the human primary motor cortex. Stained brain slice images which include the "Betz cell" at the BrainMaps project NIF Search - Betz Cell via the Neuroscience Information Framework
Stellate cells are any neuron in the central nervous system that have a star-like shape formed by dendritic processes radiating from the cell body. Many Stellate cells are located in the molecular layer of the cerebellum. Stellate cells are derived from dividing progenitors in the white matter of postnatal cerebellum. Dendritic trees can vary between neurons. There are two types of dendritic trees in the cerebral cortex, which include pyramidal cells, which are pyramid shaped and stellate cells which are star shaped. Dendrites can aid neuron classification. Dendrites with spines are classified as spiny. Stellate cells can be aspinous, while pyramidal cells are always spiny. Most common stellate cells are the inhibitory interneurons found within the upper half of the molecular layer in the cerebellum. Cerebellar stellate cells synapse onto the dendritic arbors of Purkinje cells and send inhibitory signals. Stellate neurons are sometimes found in other locations in the central nervous system. In the somatosensory barrel cortex of mice and rats, glutamatergic spiny stellate cells are organized in the barrels of layer 4.
They receive excitatory synaptic fibres from the thalamus and process feed forward excitation to 2/3 layer of V1 visual cortex to pyramidal cells. Cortical spiny stellate cells have a'regular' firing pattern. Stellate cells are chromophobes, cells that does not stain and thus appears pale under the microscope. Cerebellar Stellate Cells are GABAergic. Stellate and basket cells originate from the cerebellar ventricular zone along with Purkinje cells and Bergmann glia Due to their similarity and stellate cells are grouped together when examined during migration given they follow the same pathway. After mitosis, these cells start in the deep layer of the white matter and migrate up through the internal granular layer and purkinje cell layer until they reach the molecular layer. During their time in the molecular layer, they change orientation and positioning until they end up in the middle portion of this layer, facing the rostrocaudal direction. Once in this layer, the stellate cells are guided to their correct placement by Bergman glial cells.
Aspinous stellate cells are GABAergic cells. Apart from visual classification of the aspinous dendrites, they can be immunohistochemically labelled with glutamic acid decarboxylase because of their GABAergic activity, colocalize with neuropeptides. Stellate ganglion NIF Search - Stellate Cell via the Neuroscience Information Framework
The cerebral cortex known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain, in humans and other mammals. It is separated into two cortices, by the longitudinal fissure that divides the cerebrum into the left and right cerebral hemispheres; the two hemispheres are joined beneath the cortex by the corpus callosum. The cerebral cortex is the largest site of neural integration in the central nervous system, it plays a key role in memory, perception, thought and consciousness. In most mammals, apart from small mammals that have small brains, the cerebral cortex is folded, providing a greater surface area in the confined volume of the cranium. Apart from minimising brain and cranial volume cortical folding is crucial for the wiring of the brain and its functional organisation. In mammals with a small brain there is no folding and the cortex is smooth. A fold or ridge in the cortex is termed a gyrus and a groove is termed a sulcus; these surface convolutions appear during fetal development and continue to mature after birth through the process of gyrification.
In the human brain the majority of the cerebral cortex is not visible from the outside, but buried in the sulci, the insular cortex is hidden. The major sulci and gyri mark the divisions of the cerebrum into the lobes of the brain. There are between 16 billion neurons in the cerebral cortex; these are organised into cortical columns and minicolumns of neurons that make up the layers of the cortex. Most of the cerebral cortex consists of the six-layered neocortex. Cortical areas have specific functions; the cerebral cortex is the outer covering of the surfaces of the cerebral hemispheres and is folded into peaks called gyri, grooves called sulci. In the human brain it is between two and three or four millimetres thick, makes up 40 per cent of the brain's mass. There are between 14 and 16 billion neurons in the cortex, these are organized in cortical columns, minicolumns of the layers of the cortex. About two thirds of the cortical surface is buried in the sulci and the insular cortex is hidden; the cortex is thickest over thinnest at the bottom of a sulcus.
The cerebral cortex is folded in a way that allows a large surface area of neural tissue to fit within the confines of the neurocranium. When unfolded in the human, each hemispheric cortex has a total surface area of about 1.3 square feet. The folding is inward away from the surface of the brain, is present on the medial surface of each hemisphere within the longitudinal fissure. Most mammals have a cerebral cortex, convoluted with the peaks known as gyri and the troughs or grooves known as sulci; some small mammals including some small rodents have smooth cerebral surfaces without gyrification. The larger sulci and gyri mark the divisions of the cortex of the cerebrum into the lobes of the brain. There are four main lobes: the frontal lobe, parietal lobe, temporal lobe, occipital lobe; the insular cortex is included as the insular lobe. The limbic lobe is a rim of cortex on the medial side of each hemisphere and is often included. There are three lobules of the brain described: the paracentral lobule, the superior parietal lobule, the inferior parietal lobule.
For species of mammals, larger brains tend to have thicker cortices. The smallest mammals, such as shrews, have a neocortical thickness of about 0.5 mm. There is an logarithmic relationship between brain weight and cortical thickness. Magnetic resonance imaging of the brain makes it possible to get a measure for the thickness of the human cerebral cortex and relate it to other measures; the thickness of different cortical areas varies but in general, sensory cortex is thinner than motor cortex. One study has found some positive association between the cortical intelligence. Another study has found that the somatosensory cortex is thicker in migraine sufferers, though it is not known if this is the result of migraine attacks or the cause of them. A study using a larger patient population reports no change in the cortical thickness in migraine sufferers. A genetic disorder of the cerebral cortex, whereby decreased folding in certain areas results in a microgyrus, where there are four layers instead of six, is in some instances seen to be related to dyslexia.
The six cortical layers of the neocortex each contain a characteristic distribution of different neurons and their connections with other cortical and subcortical regions. There are direct connections between different cortical areas and indirect connections via the thalamus. One of the clearest examples of cortical layering is the line of Gennari in the primary visual cortex; this is a band of whiter tissue that can be observed with the naked eye in the fundus of the calcarine sulcus of the occipital lobe. The line of Gennari is composed of axons bringing visual information from the thalamus into layer IV of the visual cortex. Staining cross-sections of the cortex to reveal the position of neuronal cell bodies and the intracortical axon tracts allowed neuroanatomists in the early 20th century to produce a detailed description of the laminar structure of the cortex in different species. After the work of Korbinian Brodmann the neurons of the cerebral cortex are grouped into six main layers, from the outer pial surface to the inner white matter.
Layer I is the molecular layer, contains few scattered neurons, including GABAergic rosehip neurons. Layer I consists of extensions of apical dendritic tufts of pyramidal neurons and horiz