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In networks-based biocomputation, self-propelled biological agents, such as molecular motor proteins or bacteria, explore a microscopic network that encodes a mathematical problem of interest. The paths of the agents through the network and/or their final positions represent potential solutions to the problem. For instance, in the system described by Nicolau et al., mobile molecular motor filaments are detected at the "exits" of a network encoding the NP-complete problem SUBSET SUM. All exits visited by filaments represent correct solutions to the algorithm. | https://en.wikipedia.org/wiki/Biological_computing |
Exits not visited are non-solutions. The motility proteins are either actin and myosin or kinesin and microtubules. | https://en.wikipedia.org/wiki/Biological_computing |
The myosin and kinesin, respectively, are attached to the bottom of the network channels. When adenosine triphosphate (ATP) is added, the actin filaments or microtubules are propelled through the channels, thus exploring the network. The energy conversion from chemical energy (ATP) to mechanical energy (motility) is highly efficient when compared with e.g. electronic computing, so the computer, in addition to being massively parallel, also uses orders of magnitude less energy per computational step. | https://en.wikipedia.org/wiki/Biological_computing |
In neural network applications, the number K of possible outcomes is often large, e.g. in case of neural language models that predict the most likely outcome out of a vocabulary which might contain millions of possible words. This can make the calculations for the softmax layer (i.e. the matrix multiplications to determine the z i {\displaystyle z_{i}} , followed by the application of the softmax function itself) computationally expensive. What's more, the gradient descent backpropagation method for training such a neural network involves calculating the softmax for every training example, and the number of training examples can also become large. The computational effort for the softmax became a major limiting factor in the development of larger neural language models, motivating various remedies to reduce training times.Approaches that reorganize the softmax layer for more efficient calculation include the hierarchical softmax and the differentiated softmax. | https://en.wikipedia.org/wiki/Softmax_activation_function |
The hierarchical softmax (introduced by Morin and Bengio in 2005) uses a binary tree structure where the outcomes (vocabulary words) are the leaves and the intermediate nodes are suitably selected "classes" of outcomes, forming latent variables. The desired probability (softmax value) of a leaf (outcome) can then be calculated as the product of the probabilities of all nodes on the path from the root to that leaf. Ideally, when the tree is balanced, this would reduce the computational complexity from O ( K ) {\displaystyle O(K)} to O ( log 2 K ) {\displaystyle O(\log _{2}K)} . | https://en.wikipedia.org/wiki/Softmax_activation_function |
In practice, results depend on choosing a good strategy for clustering the outcomes into classes. A Huffman tree was used for this in Google's word2vec models (introduced in 2013) to achieve scalability.A second kind of remedies is based on approximating the softmax (during training) with modified loss functions that avoid the calculation of the full normalization factor. These include methods that restrict the normalization sum to a sample of outcomes (e.g. Importance Sampling, Target Sampling). | https://en.wikipedia.org/wiki/Softmax_activation_function |
In neural networking or heuristic algorithms (computer terms generally used to describe 'learning' computers or 'AI simulations'), a black box is used to describe the constantly changing section of the program environment which cannot easily be tested by the programmers. This is also called a white box in the context that the program code can be seen, but the code is so complex that it is functionally equivalent to a black box. In physics, a black box is a system whose internal structure is unknown, or need not be considered for a particular purpose. In cryptography to capture the notion of knowledge obtained by an algorithm through the execution of a cryptographic protocol such as a zero-knowledge proof protocol. If the output of an algorithm when interacting with the protocol matches that of a simulator given some inputs, it only needs to know the inputs. | https://en.wikipedia.org/wiki/Black_box |
In neural networks, each neuron receives input from some number of locations in the previous layer. In a convolutional layer, each neuron receives input from only a restricted area of the previous layer called the neuron's receptive field. Typically the area is a square (e.g. 5 by 5 neurons). Whereas, in a fully connected layer, the receptive field is the entire previous layer. | https://en.wikipedia.org/wiki/Pooling_(neural_networks) |
Thus, in each convolutional layer, each neuron takes input from a larger area in the input than previous layers. This is due to applying the convolution over and over, which takes the value of a pixel into account, as well as its surrounding pixels. | https://en.wikipedia.org/wiki/Pooling_(neural_networks) |
When using dilated layers, the number of pixels in the receptive field remains constant, but the field is more sparsely populated as its dimensions grow when combining the effect of several layers. To manipulate the receptive field size as desired, there are some alternatives to the standard convolutional layer. For example, atrous or dilated convolution expands the receptive field size without increasing the number of parameters by interleaving visible and blind regions. Moreover, a single dilated convolutional layer can comprise filters with multiple dilation ratios, thus having a variable receptive field size. | https://en.wikipedia.org/wiki/Pooling_(neural_networks) |
In neuroanatomy, a neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable neurotransmission (the sending of a signal from one region of the nervous system to another). Neurons are connected by a single axon, or by a bundle of axons known as a nerve tract, or fasciculus. Shorter neural pathways are found within grey matter in the brain, whereas longer projections, made up of myelinated axons, constitute white matter. In the hippocampus there are neural pathways involved in its circuitry including the perforant pathway, that provides a connectional route from the entorhinal cortex to all fields of the hippocampal formation, including the dentate gyrus, all CA fields (including CA1), and the subiculum. Descending motor pathways of the pyramidal tracts travel from the cerebral cortex to the brainstem or lower spinal cord. Ascending sensory tracts in the dorsal column–medial lemniscus pathway (DCML) carry information from the periphery to the cortex of the brain. | https://en.wikipedia.org/wiki/Neural_pathway |
In neuroanatomy, a plexus (from the Latin term for "braid") is a branching network of vessels or nerves. The vessels may be blood vessels (veins, capillaries) or lymphatic vessels. The nerves are typically axons outside the central nervous system. The standard plural form in English is plexuses. Alternatively, the Latin plural plexūs may be used. | https://en.wikipedia.org/wiki/Plexus |
In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. The other two meningeal layers are the arachnoid mater and the pia mater. It envelops the arachnoid mater, which is responsible for keeping in the cerebrospinal fluid. It is derived primarily from the neural crest cell population, with postnatal contributions of the paraxial mesoderm. | https://en.wikipedia.org/wiki/Dura_mater |
In neuroanatomy, habenula (diminutive of Latin habena meaning rein) originally denoted the stalk of the pineal gland (pineal habenula; pedunculus of pineal body), but gradually came to refer to a neighboring group of nerve cells with which the pineal gland was believed to be associated, the habenular nucleus. The habenular nucleus is a set of well-conserved structures in all vertebrate animals.Currently, this term refers to this separate cell mass in the caudal portion of the dorsal diencephalon, known as the epithalamus, found in all vertebrates on both sides of the third ventricle. It connects the forebrain and midbrain within the epithalamus. It is embedded in the posterior end of the stria medullaris from which it receives most of its afferent fibers. | https://en.wikipedia.org/wiki/Lateral_habenula |
By way of the fasciculus retroflexus (habenulointerpeduncular tract) it projects to the interpeduncular nucleus and other paramedian cell groups of the midbrain tegmentum. Although they were predominantly studied for their demonstration of asymmetrical brain development and function, in recent years many scientists have begun to examine the habenular nuclei's role in motivation and behavior as it relates to an understanding of the physiology of addiction. Functionally, the habenula is involved in nociception, sleep-wake cycles, reproductive behavioural, and mood (see section on depression below). It is one of the few areas known to influence virtually all monoaminergic systems in the brainstem, such as dopamine, norepinephrine, and serotonin. | https://en.wikipedia.org/wiki/Lateral_habenula |
In neuroanatomy, thalamocortical radiations also known as thalamocortical fibres, are the efferent fibres that project from the thalamus to distinct areas of the cerebral cortex. They form fibre bundles that emerge from the lateral surface of the thalamus. | https://en.wikipedia.org/wiki/Thalamocortical_radiation |
In neuroanatomy, the arcuate fasciculus (AF; from Latin 'curved bundle') is a bundle of axons that generally connects the Broca's area and the Wernicke's area in the brain. It is an association fiber tract connecting caudal temporal cortex and inferior frontal lobe. | https://en.wikipedia.org/wiki/Arcuate_fasciculus |
In neuroanatomy, the central sulcus (also central fissure, fissure of Rolando, or Rolandic fissure, after Luigi Rolando) is a sulcus, or groove, in the cerebral cortex in the brains of vertebrates. It is sometimes confused with the longitudinal fissure. The central sulcus is a prominent landmark of the brain, separating the parietal lobe from the frontal lobe and the primary motor cortex from the primary somatosensory cortex. | https://en.wikipedia.org/wiki/Central_sulcus |
In neuroanatomy, the corona radiata is a white matter sheet that continues inferiorly as the internal capsule and superiorly as the centrum semiovale. This sheet of both ascending and descending axons carries most of the neural traffic from and to the cerebral cortex. The corona radiata is associated with the corticopontine tract, the corticobulbar tract, and the corticospinal tract. | https://en.wikipedia.org/wiki/Corona_radiata |
In neuroanatomy, the corticobulbar (or corticonuclear) tract is a two-neuron white matter motor pathway connecting the motor cortex in the cerebral cortex to the medullary pyramids, which are part of the brainstem's medulla oblongata (also called "bulbar") region, and are primarily involved in carrying the motor function of the non-oculomotor cranial nerves. The corticobulbar tract is one of the pyramidal tracts, the other being the corticospinal tract. | https://en.wikipedia.org/wiki/Corticobulbar_tract |
In neuroanatomy, the cranial nerve ganglia are ganglia of certain cranial nerves. They can be parasympathetic or sensory. All cranial nerve ganglia are bilateral. | https://en.wikipedia.org/wiki/Cranial_nerve_ganglia |
In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are situated at the lower end of the medulla oblongata. Both nuclei contain second-order neurons of the dorsal column–medial lemniscus pathway, which convey fine touch and proprioceptive information from the body to the brain. The dorsal column nuclei project to the thalamus. | https://en.wikipedia.org/wiki/Cuneate_nucleus |
In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. There are two LGNs, one on the left and another on the right side of the thalamus. In humans, both LGNs have six layers of neurons (grey matter) alternating with optic fibers (white matter). | https://en.wikipedia.org/wiki/Lateral_geniculate_body |
The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system. Neurons of the LGN send their axons through the optic radiation, a direct pathway to the primary visual cortex. In addition, the LGN receives many strong feedback connections from the primary visual cortex. In humans as well as other mammals, the two strongest pathways linking the eye to the brain are those projecting to the dorsal part of the LGN in the thalamus, and to the superior colliculus. | https://en.wikipedia.org/wiki/Lateral_geniculate_body |
In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus is a deep fissure in each hemisphere that separates the frontal and parietal lobes from the temporal lobe. The insular cortex lies deep within the lateral sulcus. | https://en.wikipedia.org/wiki/Lateral_sulcus |
In neuroanatomy, the mandibular nerve (V3) is the largest of the three divisions of the trigeminal nerve, the fifth cranial nerve (CN V). Unlike the other divisions of the trigeminal nerve (ophthalmic nerve, maxillary nerve) which contain only afferent fibers, the mandibular nerve contains both afferent and efferent fibers. These nerve fibers innervate structures of the lower jaw and face, such as the tongue, lower lip, and chin. The mandibular nerve also innervates the muscles of mastication. | https://en.wikipedia.org/wiki/Mandibular_nerve |
In neuroanatomy, the marginal sulcus (margin of the cingulate sulcus) is a sulcus (crevice) that may be considered the termination of the cingulate sulcus. It separates the paracentral lobule anteriorly and the precuneus posteriorly. | https://en.wikipedia.org/wiki/Marginal_sulcus |
In neuroanatomy, the maxillary nerve (V2) is one of the three branches or divisions of the trigeminal nerve, the fifth (CN V) cranial nerve. It comprises the principal functions of sensation from the maxilla, nasal cavity, sinuses, the palate and subsequently that of the mid-face, and is intermediate, both in position and size, between the ophthalmic nerve and the mandibular nerve. | https://en.wikipedia.org/wiki/Maxillary_nerve |
In neuroanatomy, the medial lemniscus, also known as Reil's band or Reil's ribbon (for German anatomist Johann Christian Reil), is a large ascending bundle of heavily myelinated axons that decussate (cross) in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally. The medial lemniscus is part of the dorsal column–medial lemniscus pathway, which ascends from the skin to the thalamus, which is important for somatosensation from the skin and joints, therefore, lesion of the medial lemnisci causes an impairment of vibratory and touch-pressure sense. | https://en.wikipedia.org/wiki/Medial_lemniscus |
In neuroanatomy, the medullary pyramids are paired white matter structures of the brainstem's medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit of the pyramids is marked when the fibers cross (decussate). | https://en.wikipedia.org/wiki/Decussation_of_pyramids |
In neuroanatomy, the optic chiasm, or optic chiasma ( ; from Greek χίασμα 'crossing', from Ancient Greek χιάζω 'to mark with an X'), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrates, although in cyclostomes (lampreys and hagfishes), it is located within the brain.This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)). A midline crossing of nerves inside the brain is called a decussation (see Definition of types of crossings). | https://en.wikipedia.org/wiki/Optic_chiasm |
In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus. | https://en.wikipedia.org/wiki/Optic_nerve |
In neuroanatomy, the optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic radiation receives blood through deep branches of the middle cerebral artery and posterior cerebral artery. They carry visual information through two divisions (called upper and lower division) to the visual cortex (also called striate cortex) along the calcarine fissure. There is one set of upper and lower divisions on each side of the brain. If a lesion only exists in one unilateral division of the optic radiation, the consequence is called quadrantanopia, which implies that only the respective superior or inferior quadrant of the visual field is affected. If both divisions on one side of the brain are affected, the result is a contralateral homonymous hemianopsia. | https://en.wikipedia.org/wiki/Optic_radiation |
In neuroanatomy, the optic tract (from Latin tractus opticus) is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus.It is composed of two individual tracts, the left optic tract and the right optic tract, each of which conveys visual information exclusive to its respective contralateral half of the visual field. Each of these tracts is derived from a combination of temporal and nasal retinal fibers from each eye that corresponds to one half of the visual field. In more specific terms, the optic tract contains fibers from the ipsilateral temporal hemiretina and contralateral nasal hemiretina. | https://en.wikipedia.org/wiki/Optic_tract |
In neuroanatomy, the paracentral lobule is on the medial surface of the cerebral hemisphere and is the continuation of the precentral and postcentral gyri. The paracentral lobule controls motor and sensory innervations of the contralateral lower extremity. It is also responsible for control of defecation and urination. It includes portions of the frontal and parietal lobes: The anterior portion of the paracentral lobule is part of the frontal lobe and contains a little portion of Brodmann's area 6 (SMA): this is because the paracentral sulcus (branch of the cingulate sulcus) does not correspond to the precentral sulcus on the medial plane. The posterior portion is considered part of the parietal lobe and deals with somatosensory of the distal limbs.While the boundary between the lobes, the central sulcus, is easy to locate on the lateral surface of the cerebral hemispheres, this boundary is often discerned in a cytoarchetectonic manner in cases where the central sulcus is not visible on the medial surface. | https://en.wikipedia.org/wiki/Paracentral_lobule |
In neuroanatomy, the parieto-occipital sulcus (also called the parieto-occipital fissure) is a deep sulcus in the cerebral cortex that marks the boundary between the cuneus and precuneus, and also between the parietal and occipital lobes. Only a small part can be seen on the lateral surface of the hemisphere, its chief part being on the medial surface. The lateral part of the parieto-occipital sulcus (Fig. 726) is situated about 5 cm in front of the occipital pole of the hemisphere, and measures about 1.25 cm. | https://en.wikipedia.org/wiki/Parieto-occipital_sulcus |
in length. The medial part of the parieto-occipital sulcus (Fig. 727) runs downward and forward as a deep cleft on the medial surface of the hemisphere, and joins the calcarine fissure below and behind the posterior end of the corpus callosum. In most cases, it contains a submerged gyrus. | https://en.wikipedia.org/wiki/Parieto-occipital_sulcus |
In neuroanatomy, the postcentral gyrus is a prominent gyrus in the lateral parietal lobe of the human brain. It is the location of the primary somatosensory cortex, the main sensory receptive area for the sense of touch. Like other sensory areas, there is a map of sensory space in this location, called the sensory homunculus. The primary somatosensory cortex was initially defined from surface stimulation studies of Wilder Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann areas 3, 1 and 2, more recent work by Kaas has suggested that for homogeny with other sensory fields only area 3 should be referred to as "primary somatosensory cortex", as it receives the bulk of the thalamocortical projections from the sensory input fields. | https://en.wikipedia.org/wiki/Postcentral_gyrus |
In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediating behavioral responses to acute changes in ambient light such as the pupillary light reflex, the optokinetic reflex, and temporary changes to the circadian rhythm. In addition to the pretectum's role in the visual system, the anterior pretectal nucleus has been found to mediate somatosensory and nociceptive information. | https://en.wikipedia.org/wiki/Pretectal_area |
In neuroanatomy, the primary somatosensory cortex is located in the postcentral gyrus of the brain's parietal lobe, and is part of the somatosensory system. It was initially defined from surface stimulation studies of Wilder Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann areas 3, 1 and 2, more recent work by Kaas has suggested that for homogeny with other sensory fields only area 3 should be referred to as "primary somatosensory cortex", as it receives the bulk of the thalamocortical projections from the sensory input fields.At the primary somatosensory cortex, tactile representation is orderly arranged (in an inverted fashion) from the toe (at the top of the cerebral hemisphere) to mouth (at the bottom). However, some body parts may be controlled by partially overlapping regions of cortex. | https://en.wikipedia.org/wiki/Primary_somatosensory_cortex |
Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite (contralateral) side of the body. The amount of primary somatosensory cortex devoted to a body part is not proportional to the absolute size of the body surface, but, instead, to the relative density of cutaneous tactile receptors located on that body part. The density of cutaneous tactile receptors on a body part is generally indicative of the degree of sensitivity of tactile stimulation experienced at said body part. For this reason, the human lips and hands have a larger representation than other body parts. | https://en.wikipedia.org/wiki/Primary_somatosensory_cortex |
In neuroanatomy, the retinohypothalamic tract (RHT) is a photic neural input pathway involved in the circadian rhythms of mammals. The origin of the retinohypothalamic tract is the intrinsically photosensitive retinal ganglion cells (ipRGC), which contain the photopigment melanopsin. The axons of the ipRGCs belonging to the retinohypothalamic tract project directly, monosynaptically, to the suprachiasmatic nuclei (SCN) via the optic nerve and the optic chiasm. The suprachiasmatic nuclei receive and interpret information on environmental light, dark and day length, important in the entrainment of the "body clock". They can coordinate peripheral "clocks" and direct the pineal gland to secrete the hormone melatonin. | https://en.wikipedia.org/wiki/Retinohypothalamic_tract |
In neuroanatomy, the sensory decussation or decussation of the lemnisci is a decussation (i.e. crossover) of axons from the gracile nucleus and cuneate nucleus, which are responsible for fine touch, vibration, proprioception and two-point discrimination of the body. The fibres of this decussation are called the internal arcuate fibres and are found at the superior aspect of the closed medulla superior to the motor decussation. It is part of the second neuron in the posterior column–medial lemniscus pathway. | https://en.wikipedia.org/wiki/Sensory_decussation |
In neuroanatomy, the superior colliculus (from Latin 'upper hill') is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum, or optic lobe. The adjective form tectal is commonly used for both structures. | https://en.wikipedia.org/wiki/Superior_colliculus |
In mammals, the superior colliculus forms a major component of the midbrain. It is a paired structure and together with the paired inferior colliculi forms the corpora quadrigemina. The superior colliculus is a layered structure, with a pattern that is similar to all mammals. | https://en.wikipedia.org/wiki/Superior_colliculus |
The layers can be grouped into the superficial layers (stratum opticum and above) and the deeper remaining layers. Neurons in the superficial layers receive direct input from the retina and respond almost exclusively to visual stimuli. Many neurons in the deeper layers also respond to other modalities, and some respond to stimuli in multiple modalities. | https://en.wikipedia.org/wiki/Superior_colliculus |
The deeper layers also contain a population of motor-related neurons, capable of activating eye movements as well as other responses. In other vertebrates the number of layers in the homologous optic tectum varies.The general function of the tectal system is to direct behavioral responses toward specific points in body-centered space. Each layer contains a topographic map of the surrounding world in retinotopic coordinates, and activation of neurons at a particular point in the map evokes a response directed toward the corresponding point in space. | https://en.wikipedia.org/wiki/Superior_colliculus |
In primates, the superior colliculus has been studied mainly with respect to its role in directing eye movements. Visual input from the retina, or "command" input from the cerebral cortex, create a "bump" of activity in the tectal map, which, if strong enough, induces a saccadic eye movement. Even in primates, however, the superior colliculus is also involved in generating spatially directed head turns, arm-reaching movements, and shifts in attention that do not involve any overt movements. | https://en.wikipedia.org/wiki/Superior_colliculus |
In other species, the superior colliculus is involved in a wide range of responses, including whole-body turns in walking rats. In mammals, and especially primates, the massive expansion of the cerebral cortex reduces the superior colliculus to a much smaller fraction of the whole brain. It remains nonetheless important in terms of function as the primary integrating center for eye movements. | https://en.wikipedia.org/wiki/Superior_colliculus |
In non-mammalian species the optic tectum is involved in many responses including swimming in fish, flying in birds, tongue-strikes toward prey in frogs, and fang-strikes in snakes. In some species, including fish and birds, the optic tectum, also known as the optic lobe, is one of the largest components of the brain. Note on terminology: This article follows terminology established in the literature, using the term "superior colliculus" when discussing mammals and "optic tectum" when discussing either specific non-mammalian species or vertebrates in general. | https://en.wikipedia.org/wiki/Superior_colliculus |
In neuroanatomy, the superior frontal gyrus (SFG, also marginal gyrus) is a gyrus – a ridge on the brain's cerebral cortex – which makes up about one third of the frontal lobe. It is bounded laterally by the superior frontal sulcus.The superior frontal gyrus is one of the frontal gyri. | https://en.wikipedia.org/wiki/Superior_frontal_gyrus |
In neuroanatomy, the trigeminal nerve (lit. triplet nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewing; it is the most complex of the cranial nerves. Its name (trigeminal, from Latin tri- 'three', and -geminus 'twin') derives from each of the two nerves (one on each side of the pons) having three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3). The ophthalmic and maxillary nerves are purely sensory, whereas the mandibular nerve supplies motor as well as sensory (or "cutaneous") functions. | https://en.wikipedia.org/wiki/Trigeminal_system |
Adding to the complexity of this nerve is that autonomic nerve fibers as well as special sensory fibers (taste) are contained within it. The motor division of the trigeminal nerve derives from the basal plate of the embryonic pons, and the sensory division originates in the cranial neural crest. Sensory information from the face and body is processed by parallel pathways in the central nervous system. | https://en.wikipedia.org/wiki/Trigeminal_system |
In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception. | https://en.wikipedia.org/wiki/Lateral_inhibition |
It is also referred to as lateral antagonism and occurs primarily in visual processes, but also in tactile, auditory, and even olfactory processing. Cells that utilize lateral inhibition appear primarily in the cerebral cortex and thalamus and make up lateral inhibitory networks (LINs). Artificial lateral inhibition has been incorporated into artificial sensory systems, such as vision chips, hearing systems, and optical mice. | https://en.wikipedia.org/wiki/Lateral_inhibition |
An often under-appreciated point is that although lateral inhibition is visualised in a spatial sense, it is also thought to exist in what is known as "lateral inhibition across abstract dimensions." This refers to lateral inhibition between neurons that are not adjacent in a spatial sense, but in terms of modality of stimulus. This phenomenon is thought to aid in colour discrimination. | https://en.wikipedia.org/wiki/Lateral_inhibition |
In neurobiology, the length constant (λ) is a mathematical constant used to quantify the distance that a graded electric potential will travel along a neurite via passive electrical conduction. The greater the value of the length constant, the farther the potential will travel. A large length constant can contribute to spatial summation—the electrical addition of one potential with potentials from adjacent areas of the cell. The length constant can be defined as: λ = r m r i + r o {\displaystyle \lambda ={\sqrt {\frac {r_{m}}{r_{i}+r_{o}}}}} where rm is the membrane resistance (the force that impedes the flow of electric current from the outside of the membrane to the inside, and vice versa), ri is the axial resistance (the force that impedes current flow through the axoplasm, parallel to the membrane), and ro is the extracellular resistance (the force that impedes current flow through the extracellular fluid, parallel to the membrane). | https://en.wikipedia.org/wiki/Length_constant |
In calculation, the effects of ro are negligible, so the equation is typically expressed as: λ = r m r i {\displaystyle \lambda ={\sqrt {\frac {r_{m}}{r_{i}}}}} The membrane resistance is a function of the number of open ion channels, and the axial resistance is generally a function of the diameter of the axon. The greater the number of open channels, the lower the rm. The greater the diameter of the axon, the lower the ri. | https://en.wikipedia.org/wiki/Length_constant |
The length constant is used to describe the rise of potential difference across the membrane V ( x ) = V max ( 1 − e − x / λ ) {\displaystyle V(x)=V_{\max }\left(1-e^{-x/\lambda }\right)} The fall of voltage can be expressed as: V ( x ) = V max e − x / λ {\displaystyle V(x)=V_{\max }e^{-x/\lambda }} Where voltage, V, is measured in millivolts, x is distance from the start of the potential (in millimeters), and λ is the length constant (in millimeters). Vmax is defined as the maximum voltage attained in the action potential, where: V max = r m I {\displaystyle V_{\max }=r_{m}I} where rm is the resistance across the membrane and I is the current flow. Setting for x = λ for the rise of voltage sets V(x) equal to .63 Vmax. This means that the length constant is the distance at which 63% of Vmax has been reached during the rise of voltage. Setting for x = λ for the fall of voltage sets V(x) equal to .37 Vmax, meaning that the length constant is the distance at which 37% of Vmax has been reached during the fall of voltage. | https://en.wikipedia.org/wiki/Length_constant |
In neuroenhancement, the human brain is conceived of as a malleable "wetware". | https://en.wikipedia.org/wiki/Neuroenhancement |
In neuroethology and the study of learning, anti-Hebbian learning describes a particular class of learning rule by which synaptic plasticity can be controlled. These rules are based on a reversal of Hebb's postulate, and therefore can be simplistically understood as dictating reduction of the strength of synaptic connectivity between neurons following a scenario in which a neuron directly contributes to production of an action potential in another neuron. | https://en.wikipedia.org/wiki/Anti-Hebbian_learning |
In neurogenesis, Sox2 is expressed throughout developing cells in the neural tube as well as in proliferating central nervous system progenitors. However, Sox2 is downregulated during progenitors' final cell cycle during differentiation when they become post mitotic. Cells expressing Sox2 are capable of both producing cells identical to themselves and differentiated neural cell types, two necessary hallmarks of stem cells. | https://en.wikipedia.org/wiki/SOX2 |
Thus signals controlling Sox2 expression in the presumptive neuronal compartment, like Notch signaling, control what size the neuronal compartment finally reaches. Proliferation of Sox2+ neural stem cells can generate neural precursors as well as Sox2+ neural stem cell population. Differences in brain size between the species thus relate to the capacity of different species to maintain SOX2 expression in the developing neural systems. The difference in brain size between humans and apes, for instance, has been linked to mutations in the gene Asb11, which is an upstream activator of SOX2 in the developing neural system.Induced pluripotency is possible using adult neural stem cells, which express higher levels of Sox2 and c-Myc than embryonic stem cells. Therefore, only two exogenous factors, one of which is necessarily Oct4, are sufficient for inducing pluripotent cells from neural stem cells, lessening the complications and risks associated with introducing multiple factors to induce pluripotency. | https://en.wikipedia.org/wiki/SOX2 |
In neuroimaging, spatial normalization is an image processing step, more specifically an image registration method. Human brains differ in size and shape, and one goal of spatial normalization is to deform human brain scans so one location in one subject's brain scan corresponds to the same location in another subject's brain scan. It is often performed in research-based functional neuroimaging where one wants to find common brain activation across multiple human subjects. The brain scan can be obtained from magnetic resonance imaging (MRI) or positron emission tomography (PET) scanners. | https://en.wikipedia.org/wiki/Spatial_normalization |
There are two steps in the spatial normalization process: Specification/estimation of warp-field Application of warp-field with resamplingThe estimation of the warp-field can be performed in one modality, e.g., MRI, and be applied in another modality, e.g., PET, if MRI and PET scans exist for the same subject and they are coregistered. Spatial normalization typically employs a 3-dimensional nonrigid transformation model (a "warp-field") for warping a brain scan to a template. The warp-field might be parametrized by basis functions such as cosine and polynomia. | https://en.wikipedia.org/wiki/Spatial_normalization |
In neuroimaging, the most common variants are voxel-based morphometry, deformation-based morphometry and surface-based morphometry of the brain. | https://en.wikipedia.org/wiki/Morphometrics |
In neurology and neuroscience research, steady state visually evoked potentials (SSVEPs) are signals that are natural responses to visual stimulation at specific frequencies. When the retina is excited by a visual stimulus ranging from 3.5 Hz to 75 Hz, the brain generates electrical activity at the same (or multiples of) frequency of the visual stimulus. SSVEPs are typically measured using electroencephalography. SSVEPs are useful in research because of the excellent signal-to-noise ratio and relative immunity to artifacts. | https://en.wikipedia.org/wiki/Steady_state_visually_evoked_potential |
SSVEPs also provide a means to characterize preferred frequencies of neocortical dynamic processes. SSVEPs are generated by stationary localized sources and distributed sources that exhibit characteristics of wave phenomena. SSVEPs have been widely used in vision, cognitive neuroscience (e.g., visual attention, binocular rivalry, working memory, alpha range), and clinical neuroscience (e.g., aging and neurodegenerative disorders, schizophrenia, epilepsy) research. They are also used for brain-computer-interfaces. | https://en.wikipedia.org/wiki/Steady_state_visually_evoked_potential |
In neurology, anterograde amnesia is the inability to create new memories after an event that caused amnesia, leading to a partial or complete inability to recall the recent past, while long-term memories from before the event remain intact. This is in contrast to retrograde amnesia, where memories created prior to the event are lost while new memories can still be created. Both can occur together in the same patient. To a large degree, anterograde amnesia remains a mysterious ailment because the precise mechanism of storing memories is not yet well understood, although it is known that the regions of the brain involved are certain sites in the temporal cortex, especially in the hippocampus and nearby subcortical regions. | https://en.wikipedia.org/wiki/Anterograde_amnesia |
In neurology, retrograde amnesia (RA) is the inability to access memories or information from before an injury or disease occurred. RA differs from a similar condition called anterograde amnesia (AA), which is the inability to form new memories following injury or disease onset. Although an individual can have both RA and AA at the same time, RA can also occur on its own; this 'pure' form of RA can be further divided into three types: focal, isolated, and pure RA. RA negatively affects an individual's episodic, autobiographical, and declarative memory, but they can still form new memories because RA leaves procedural memory intact. | https://en.wikipedia.org/wiki/Retrograde_amnesia |
Depending on its severity, RA can result in either temporally graded or more permanent memory loss. However, memory loss usually follows Ribot's law, which states that individuals are more likely to lose recent memories than older memories. Diagnosing RA generally requires using an Autobiographical Memory Interview (AMI) and observing brain structure through magnetic resonance imaging (MRI), a computed tomography scan (CT), or electroencephalography (EEG). | https://en.wikipedia.org/wiki/Retrograde_amnesia |
In neurology, the Bereitschaftspotential or BP (German for "readiness potential"), also called the pre-motor potential or readiness potential (RP), is a measure of activity in the motor cortex and supplementary motor area of the brain leading up to voluntary muscle movement. The BP is a manifestation of cortical contribution to the pre-motor planning of volitional movement. It was first recorded and reported in 1964 by Hans Helmut Kornhuber and Lüder Deecke at the University of Freiburg in Germany. In 1965 the full publication appeared after many control experiments. | https://en.wikipedia.org/wiki/Bereitschaftspotential |
In neurometabolic diseases, distended storage neurons are markedly swollen and pear shaped, with the nucleus and the nissl bodies displaced toward the apical dendrites. Examples of neuron metabolic storage diseases are the sphingolipid storage diseases which typically involve malfunctioning hydrolases in the lysosomes responsible for the degradation of these lipids: type 2 and type 3 Gaucher disease GM1 gangliosidosis and GM2 gangliosidosisThis swelling is shown, for instance, in Tay–Sachs disease, a GM2 accumulation due to defective beta-hexosaminidase. Visible in this disorder are large mega-neurite formations. | https://en.wikipedia.org/wiki/Apical_dendrite |
In neuronal cells, CCAT is generated upon activation of a cryptic promoter in exon 46 of CACNA1C, the gene that encodes the voltage-gated calcium channel Cav1.2. == References == | https://en.wikipedia.org/wiki/Calcium_channel_associated_transcriptional_regulator |
In neuronal exocytosis, the term priming has been used to include all of the molecular rearrangements and ATP-dependent protein and lipid modifications that take place after initial docking of a synaptic vesicle but before exocytosis, such that the influx of calcium ions is all that is needed to trigger nearly instantaneous neurotransmitter release. In other cell types, whose secretion is constitutive (i.e. continuous, calcium ion independent, non-triggered) there is no priming. | https://en.wikipedia.org/wiki/Exocytosis |
In neurons of the human brain, somatic recombination occurs frequently in the gene that encodes APP. Neurons from individuals with sporadic Alzheimer's disease show greater APP gene diversity due to somatic recombination than neurons from healthy individuals. | https://en.wikipedia.org/wiki/Amyloid-beta_precursor_protein |
In neurons that are involved in chemical synaptic transmission, neurotransmitters are synthesized either in the neuronal cell body, or within the presynaptic terminal, depending on the type of neurotransmitter being synthesized and the location of enzymes involved in its synthesis. These neurotransmitters are stored in synaptic vesicles that remain bound near the membrane by calcium-influenced proteins. In order to trigger the process of chemical synaptic transmission, upstream activity causes an action potential to invade the presynaptic terminal. This depolarizing current reaches the presynaptic terminal, and the membrane depolarization that it causes there initiates the opening of voltage-gated calcium channels present on the presynaptic membrane. | https://en.wikipedia.org/wiki/Excitatory_synapse |
There is high concentration of calcium in the synaptic cleft between the two participating neurons (presynaptic and postsynaptic). This difference in calcium concentration between the synaptic cleft and the inside of the presynaptic terminal establishes a strong concentration gradient that drives the calcium into the presynaptic terminal upon opening of these voltage-gated calcium channels. This influx of calcium into the presynaptic terminal is necessary for neurotransmitter release. | https://en.wikipedia.org/wiki/Excitatory_synapse |
After entering the presynaptic terminal, the calcium binds a protein called synaptotagmin, which is located on the membrane of the synaptic vesicles. This protein interacts with other proteins called SNAREs in order to induce vesicle fusion with the presynaptic membrane. As a result of this vesicle fusion, the neurotransmitters that had been packaged into the synaptic vesicle are released into the synapse, where they diffuse across the synaptic cleft. | https://en.wikipedia.org/wiki/Excitatory_synapse |
These neurotransmitters bind to a variety of receptors on the postsynaptic cell membrane. In response to neurotransmitter binding, these postsynaptic receptors can undergo conformational changes that may open a transmembrane channel subunit either directly, or indirectly via a G-Protein signaling pathway. The selective permeability of these channels allow certain ions to move along their electrochemical gradients, inducing a current across the postsynaptic membrane that determines an excitatory or inhibitory response. | https://en.wikipedia.org/wiki/Excitatory_synapse |
In neurons, action potentials induce neurotransmitter release at axon terminals by opening voltage-gated Ca2+ channels, allowing for Ca2+ influx. As a result, GCaMP is commonly used to measure increases in intracellular Ca2+ in neurons as a proxy for neuronal activity in multiple animal models, including Caenorhabditis elegans, zebrafish, Drosophila, and mice. Recently, genetically encoded voltage indicators (GEVIs) have been developed alongside GECIs to more directly probe neuronal activity at the cellular level in these animal models.GCaMP has played a vital role in establishing large-scale neural recordings in animals to investigate how activity patterns in neuronal networks influence behavior. For example, Nguyen et al. (2016) used GCaMP in whole-brain imaging during free movement of C. elegans to identify neurons and groups of neurons whose activity correlated with specific locomotor behaviors.Muto et al. (2003) expressed GCaMP in zebrafish embryos to measure and map the coordinated activity of spinal motor neurons to different parts of the brain during the onset, propagation, and recovery of seizures induced by pentylenetetrazol. | https://en.wikipedia.org/wiki/GCaMP |
GCaMP expression in zebrafish brains has also been used to study activation of neural circuits in cognitive processes like prey capture, impulse control, and attention.Additionally, researchers have used GCaMP to observe neuronal activity in mice by expressing it under control of the Thy1 promoter, which is found in excitatory pyramidal neurons. For instance, integration of neurons into circuits during motor learning has been tracked by using GCaMP to observe synchronized fluctuation patterns in Ca2+ levels. GCaMP has also been used to observe Ca2+ dynamics in subcellular compartments of mouse neurons: Cichon and Gan (2015) used GCaMP to show that neurons in the mouse motor cortex exhibit NMDA-driven increases in Ca2+ that are independent for each dendritic spine, thus showing that individual dendritic spines regulate synaptic plasticity. | https://en.wikipedia.org/wiki/GCaMP |
Finally, GCaMP has been used to identify activity patterns in specific regions of the mouse brain. For instance, Jones et al. (2018) used GCaMP6 in mice to measure neuronal activity in the suprachiasmatic nucleus (SCN), the mammalian circadian pacemaker, and showed that SCN neurons that produced vasoactive intestinal peptide (VIP) exhibited daily activity rhythms in vivo that correlated with VIP release.GCaMP has also been combined with fiber photometry to measure population-level Ca2+ changes within subpopulations of neurons in freely moving animals. For instance, Clarkson et al. (2017) used this method to show that neurons in the arcuate nucleus of the hypothalamus synchronize to increases in Ca2+ immediately prior to pulses of luteinizing hormone (LH). While GCaMP imaging with fiber photometry cannot track changes in Ca2+ levels within individual neurons, it provides greater temporal resolution for large-scale changes. | https://en.wikipedia.org/wiki/GCaMP |
In neurons, autophagosomes are generated at the neurite tip and mature (acidify) as they travel towards the cell body along the axon. This axonal transport is disrupted if huntingtin or its interacting partner HAP1, which colocalize with autophagosomes in neurons, are depleted. == References == | https://en.wikipedia.org/wiki/Autophagosome |
In neurons, concomitant increases in cytosolic and mitochondrial Ca2+ are important for the synchronization of neuronal electrical activity with mitochondrial energy metabolism. Mitochondrial matrix Ca2+ levels can reach the tens of μM levels that are necessary for the activation of isocitrate dehydrogenase, which is one of the key regulatory enzymes of the Krebs cycle.The ER, in neurons, may serve in a network integrating numerous extracellular and intracellular signals in a binary membrane system with the plasma membrane. Such an association with the plasma membrane creates the relatively new perception of the ER and theme of "a neuron within a neuron." The ER's structural characteristics, ability to act as a Ca2+ sink, and specific Ca2+ releasing proteins, serve to create a system that may produce regenerative waves of Ca2+ release. | https://en.wikipedia.org/wiki/Calcium_signalling |
These may communicate both locally and globally in the cell. These Ca2+ signals integrate extracellular and intracellular fluxes, and have been implicated to play roles in synaptic plasticity, memory, neurotransmitter release, neuronal excitability, and long term changes at the gene transcription level. ER stress is also related to Ca2+ signaling and along with the unfolded protein response, can cause ER associated degradation (ERAD) and autophagy.Astrocytes have a direct relationship with neurons through them releasing gliotransmitters. | https://en.wikipedia.org/wiki/Calcium_signalling |
These transmitters allow communication between neurons and are triggered by calcium levels increasing around astrocytes from inside stores. This increase in calcium can also be caused by other neurotransmitters. Some examples of gliotransmitters are ATP and glutamate. Activation of these neurons will lead to an increase in the concentration of calcium in the cytosol from 100 nanomolar to 1 micromolar. | https://en.wikipedia.org/wiki/Calcium_signalling |
In neuropathy associated with diabetes mellitus characterized by alteration in small nerve fibers, a reduction in time domain parameters of HRV seems not only to carry negative prognostic value but also to precede the clinical expression of autonomic neuropathy. In diabetic patients without evidence of autonomic neuropathy, reduction of the absolute power of LF and HF during controlled conditions was also reported. Similarly, diabetic patients can be differentiated from normal controls on the basis of reduction in HRV. | https://en.wikipedia.org/wiki/Heart_rate_variability |
In neurophysiological studies, the motor system is modeled as a distributed, often hierarchical system with the spinal cord controlling the "most automatic" of movements such as stretch reflexes, and the cortex controlling the "most voluntary" actions such as reaching for an object, with the brainstem performing a function somewhere in between the two. Such studies seek to investigate how the primary motor cortex (M1) controls planning and execution of motor tasks. Traditionally, neurophysiological studies have used animal models with electrophysiological recordings and stimulation to better understand human motor control. | https://en.wikipedia.org/wiki/Degrees_of_Freedom_Problem_(Motor_Control) |
In neurophysiology, a dendritic spike refers to an action potential generated in the dendrite of a neuron. Dendrites are branched extensions of a neuron. They receive electrical signals emitted from projecting neurons and transfer these signals to the cell body, or soma. | https://en.wikipedia.org/wiki/Dendritic_spike |
Dendritic signaling has traditionally been viewed as a passive mode of electrical signaling. Unlike its axon counterpart which can generate signals through action potentials, dendrites were believed to only have the ability to propagate electrical signals by physical means: changes in conductance, length, cross sectional area, etc. However, the existence of dendritic spikes was proposed and demonstrated by W. Alden Spencer, Eric Kandel, Rodolfo Llinás and coworkers in the 1960s and a large body of evidence now makes it clear that dendrites are active neuronal structures. Dendrites contain voltage-gated ion channels giving them the ability to generate action potentials. | https://en.wikipedia.org/wiki/Dendritic_spike |
Dendritic spikes have been recorded in numerous types of neurons in the brain and are thought to have great implications in neuronal communication, memory, and learning. They are one of the major factors in long-term potentiation. A dendritic spike is initiated in the same manner as that of an axonal action potential. | https://en.wikipedia.org/wiki/Dendritic_spike |
Depolarization of the dendritic membrane causes sodium and potassium voltage-gated ion channels to open. The influx of sodium ions causes an increase in voltage. If the voltage increases past a certain threshold, the sodium current activates other voltage-gated sodium channels transmitting a current along the dendrite. | https://en.wikipedia.org/wiki/Dendritic_spike |
Dendritic spikes can be generated through both sodium and calcium voltage-gated channels. Dendritic spikes usually transmit signals at a much slower rate than axonal action potentials. Local voltage thresholds for dendritic spike initiation are usually higher than that of action potential initiation in the axon; therefore, spike initiation usually requires a strong input. | https://en.wikipedia.org/wiki/Dendritic_spike |
In neurophysiology, commutation is the process by which the brain's neural circuits exhibit non-commutativity. Physiologist Douglas B. Tweed and coworkers have considered whether certain neural circuits in the brain exhibit noncommutativity and state: In noncommutative algebra, order makes a difference to multiplication, so that a × b ≠ b × a {\displaystyle a\times b\neq b\times a} . This feature is necessary for computing rotary motion, because order makes a difference to the combined effect of two rotations. It has therefore been proposed that there are non-commutative operators in the brain circuits that deal with rotations, including motor system circuits that steer the eyes, head and limbs, and sensory system circuits that handle spatial information. | https://en.wikipedia.org/wiki/Commutative_(neurophysiology) |
This idea is controversial: studies of eye and head control have revealed behaviours that are consistent with non-commutativity in the brain, but none that clearly rules out all commutative models. Tweed goes on to demonstrate non-commutative computation in the vestibulo-ocular reflex by showing that subjects rotated in darkness can hold their gaze points stable in space – correctly computing different final eye-position commands when put through the same two rotations in different orders, in a way that is unattainable by any commutative system. == References == | https://en.wikipedia.org/wiki/Commutative_(neurophysiology) |
In neurophysiology, long-term depression (LTD) is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long patterned stimulus. LTD occurs in many areas of the CNS with varying mechanisms depending upon brain region and developmental progress.As the opposing process to long-term potentiation (LTP), LTD is one of several processes that serves to selectively weaken specific synapses in order to make constructive use of synaptic strengthening caused by LTP. This is necessary because, if allowed to continue increasing in strength, synapses would ultimately reach a ceiling level of efficiency, which would inhibit the encoding of new information. Both LTD and LTP are forms of synaptic plasticity. | https://en.wikipedia.org/wiki/Long_term_depression |
In neurophysiology, peristimulus time histogram and poststimulus time histogram, both abbreviated PSTH or PST histogram, are histograms of the times at which neurons fire. It is also sometimes called pre event time histogram or PETH. These histograms are used to visualize the rate and timing of neuronal spike discharges in relation to an external stimulus or event. The peristimulus time histogram is sometimes called perievent time histogram, and post-stimulus and peri-stimulus are often hyphenated. | https://en.wikipedia.org/wiki/Post_stimulus_time_histogram |
The prefix peri, for through, is typically used in the case of periodic stimuli, in which case the PSTH show neuron firing times wrapped to one cycle of the stimulus. The prefix post is used when the PSTH shows the timing of neuron firings in response to a stimulus event or onset.To make a PSTH, a spike train recorded from a single neuron is aligned with the onset, or a fixed phase point, of an identical stimulus repeatedly presented to an animal. The aligned sequences are superimposed in time, and then used to construct a histogram. | https://en.wikipedia.org/wiki/Post_stimulus_time_histogram |
In neurophysiology, several mathematical models of the action potential have been developed, which fall into two basic types. The first type seeks to model the experimental data quantitatively, i.e., to reproduce the measurements of current and voltage exactly. The renowned Hodgkin–Huxley model of the axon from the Loligo squid exemplifies such models. Although qualitatively correct, the H-H model does not describe every type of excitable membrane accurately, since it considers only two ions (sodium and potassium), each with only one type of voltage-sensitive channel. | https://en.wikipedia.org/wiki/Quantitative_models_of_the_action_potential |
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