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Wednesday, June 7, 2023

Utopian socialism

Utopian socialism is the term often used to describe the first current of modern socialism and socialist thought as exemplified by the work of Henri de Saint-Simon, Charles Fourier, Étienne Cabet, and Robert Owen. Utopian socialism is often described as the presentation of visions and outlines for imaginary or futuristic ideal societies, with positive ideals being the main reason for moving society in such a direction. Later socialists and critics of utopian socialism viewed utopian socialism as not being grounded in actual material conditions of existing society. These visions of ideal societies competed with revolutionary and social democratic movements.

As a term or label, utopian socialism is most often applied to, or used to define, those socialists who lived in the first quarter of the 19th century who were ascribed the label utopian by later socialists as a pejorative in order to imply naïveté and to dismiss their ideas as fanciful and unrealistic. A similar school of thought that emerged in the early 20th century which makes the case for socialism on moral grounds is ethical socialism.

One key difference between utopian socialists and other socialists such as most anarchists and Marxists is that utopian socialists generally do not believe any form of class struggle or social revolution is necessary for socialism to emerge. Utopian socialists believe that people of all classes can voluntarily adopt their plan for society if it is presented convincingly. They feel their form of cooperative socialism can be established among like-minded people within the existing society and that their small communities can demonstrate the feasibility of their plan for society. Because of this tendency, utopian socialism was also related to classical radicalism, a left-wing liberal ideology.

Development

The term utopian socialism was introduced by Karl Marx in "For a Ruthless Criticism of Everything" in 1843 and then developed in The Communist Manifesto in 1848. The term was used by later socialist thinkers to describe early socialist or quasi-socialist intellectuals who created hypothetical visions of egalitarian, communal, meritocratic, or other notions of perfect societies without considering how these societies could be created or sustained.

In The Poverty of Philosophy, Marx criticized the economic and philosophical arguments of Proudhon set forth in The System of Economic Contradictions, or The Philosophy of Poverty. Marx accused Proudhon of wanting to rise above the bourgeoisie. In the history of Marx's thought and Marxism, this work is pivotal in the distinction between the concepts of utopian socialism and what Marx and the Marxists claimed as scientific socialism. Although utopian socialists shared few political, social, or economic perspectives, Marx and Engels argued that they shared certain intellectual characteristics. In The Communist Manifesto, Marx and Friedrich Engels wrote:

The undeveloped state of the class struggle, as well as their own surroundings, causes Socialists of this kind to consider themselves far superior to all class antagonisms. They want to improve the condition of every member of society, even that of the most favored. Hence, they habitually appeal to society at large, without distinction of class; nay, by preference, to the ruling class. For how can people, when once they understand their system, fail to see it in the best possible plan of the best possible state of society? Hence, they reject all political, and especially all revolutionary, action; they wish to attain their ends by peaceful means, and endeavor, by small experiments, necessarily doomed to failure, and by the force of example, to pave the way for the new social Gospel.

Marx and Engels associated utopian socialism with communitarian socialism which similarly sees the establishment of small intentional communities as both a strategy for achieving and the final form of a socialist society. Marx and Engels used the term scientific socialism to describe the type of socialism they saw themselves developing. According to Engels, socialism was not "an accidental discovery of this or that ingenious brain, but the necessary outcome of the struggle between two historically developed classes, namely the proletariat and the bourgeoisie. Its task was no longer to manufacture a system of society as perfect as possible, but to examine the historical-economic succession of events from which these classes and their antagonism had of necessity sprung, and to discover in the economic conditions thus created the means of ending the conflict". Critics have argued that utopian socialists who established experimental communities were in fact trying to apply the scientific method to human social organization and were therefore not utopian. On the basis of Karl Popper's definition of science as "the practice of experimentation, of hypothesis and test", Joshua Muravchik argued that "Owen and Fourier and their followers were the real 'scientific socialists.' They hit upon the idea of socialism, and they tested it by attempting to form socialist communities". By contrast, Muravchik further argued that Marx made untestable predictions about the future and that Marx's view that socialism would be created by impersonal historical forces may lead one to conclude that it is unnecessary to strive for socialism because it will happen anyway.

Social unrest between the employee and employer in a society results from the growth of productive forces such as technology and natural resources are the main causes of social and economic development. These productive forces require a mode of production, or an economic system, that’s based around private property rights and institutions that determine the wage for labor.  Additionally, the capitalist rulers control the modes of production. This ideological economic structure allows the bourgeoises to undermine the worker’s sensibility of their place in society, being that the bourgeoises rule the society in their own interests. These rulers of society exploit the relationship between labor and capital, allowing for them to maximize their profit. To Marx and Engels, the profiteering through the exploitation of workers is the core issue of capitalism, explaining their beliefs for the oppression of the working class. Capitalism will reach a certain stage, one of which it cannot progress society forward, resulting in the seeding of socialism. As a socialist, Marx theorized the internal failures of capitalism. He described how the tensions between the productive forces and the modes of production would lead to the downfall of capitalism through a social revolution. Leading the revolution would be the proletariat, being that the preeminence of the bourgeoise would end. Marx’s vision of his society established that there would be no classes, freedom of mankind, and the opportunity of self-interested labor to rid any alienation. In Marx’s view, the socialist society would better the lives of the working class by introducing equality for all.

Since the mid-19th century, Engels overtook utopian socialism in terms of intellectual development and number of adherents. At one time almost half the population of the world lived under regimes that claimed to be Marxist. Currents such as Owenism and Fourierism attracted the interest of numerous later authors but failed to compete with the now dominant Marxist and Anarchist schools on a political level. It has been noted that they exerted a significant influence on the emergence of new religious movements such as spiritualism and occultism.

Utopian socialists were seen as wanting to expand the principles of the French revolution in order to create a more rational society. Despite being labeled as utopian by later socialists, their aims were not always utopian and their values often included rigid support for the scientific method and the creation of a society based upon scientific understanding.

In literature and in practice

Utopian socialist pamphlet of Swiss social medical doctor Rudolf Sutermeister (1802–1868)

Edward Bellamy (1850–1898) published Looking Backward in 1888, a utopian romance novel about a future socialist society. In Bellamy's utopia, property was held in common and money replaced with a system of equal credit for all. Valid for a year and non-transferable between individuals, credit expenditure was to be tracked via "credit-cards" (which bear no resemblance to modern credit cards which are tools of debt-finance). Labour was compulsory from age 21 to 40 and organised via various departments of an Industrial Army to which most citizens belonged. Working hours were to be cut drastically due to technological advances (including organisational). People were expected to be motivated by a Religion of Solidarity and criminal behavior was treated as a form of mental illness or "atavism". The book ranked as second or third best seller of its time (after Uncle Tom's Cabin and Ben Hur). In 1897, Bellamy published a sequel entitled Equality as a reply to his critics and which lacked the Industrial Army and other authoritarian aspects.

William Morris (1834–1896) published News from Nowhere in 1890, partly as a response to Bellamy's Looking Backwards, which he equated with the socialism of Fabians such as Sydney Webb. Morris' vision of the future socialist society was centred around his concept of useful work as opposed to useless toil and the redemption of human labour. Morris believed that all work should be artistic, in the sense that the worker should find it both pleasurable and an outlet for creativity. Morris' conception of labour thus bears strong resemblance to Fourier's, while Bellamy's (the reduction of labour) is more akin to that of Saint-Simon or in aspects Marx.

The Brotherhood Church in Britain and the Life and Labor Commune in Russia were based on the Christian anarchist ideas of Leo Tolstoy (1828–1910). Pierre-Joseph Proudhon (1809–1865) and Peter Kropotkin (1842–1921) wrote about anarchist forms of socialism in their books. Proudhon wrote What is Property? (1840) and The System of Economic Contradictions, or The Philosophy of Poverty (1847). Kropotkin wrote The Conquest of Bread (1892) and Fields, Factories and Workshops (1912). Many of the anarchist collectives formed in Spain, especially in Aragon and Catalonia, during the Spanish Civil War were based on their ideas. While linking to different topics is always useful to maximize exposure, anarchism does not derive itself from utopian socialism and most anarchists would consider the association to essentially be a marxist slur designed to reduce the credibility of anarchism amongst socialists.

Many participants in the historical kibbutz movement in Israel were motivated by utopian socialist ideas. Augustin Souchy (1892–1984) spent most of his life investigating and participating in many kinds of socialist communities. Souchy wrote about his experiences in his autobiography Beware! Anarchist! Behavioral psychologist B. F. Skinner (1904–1990) published Walden Two in 1948. The Twin Oaks Community was originally based on his ideas. Ursula K. Le Guin (1929-2018) wrote about an impoverished anarchist society in her book The Dispossessed, published in 1974, in which the anarchists agree to leave their home planet and colonize a barely habitable moon in order to avoid a bloody revolution.

Related concepts

Some communities of the modern intentional community movement such as kibbutzim could be categorized as utopian socialist. Some religious communities such as the Hutterites are categorized as utopian religious socialists.

Classless modes of production in hunter-gatherer societies are referred to as primitive communism by Marxists to stress their classless nature.

Notable utopian socialists

Notable utopian communities

Utopian communities have existed all over the world. In various forms and locations, they have existed continuously in the United States since the 1730s, beginning with Ephrata Cloister, a religious community in what is now Lancaster County, Pennsylvania.

Owenite communities
Fourierist communities
Icarian communities
Anarchist communities
Others

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Forbidden fruit

From Wikipedia, the free encyclopedia

Depiction of the original sin by Jan Brueghel de Oude and Peter Paul Rubens

Forbidden fruit is a name given to the fruit growing in the Garden of Eden which God commands mankind not to eat. In the biblical story, Adam and Eve eat the fruit from the tree of the knowledge of good and evil and are exiled from Eden.

And the Lord God commanded the man, saying, Of every tree of the garden thou mayest freely eat: But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.

— Genesis 2:16–17

As a metaphor outside of the Abrahamic religions, the phrase typically refers to any indulgence or pleasure that is considered illegal or immoral.

Biblical story

Main articles: Tree of the knowledge of good and evil and Original sin

The story of the Book of Genesis places the first man and woman, Adam and Eve, in the Garden of Eden, where they may eat the fruit of many trees, but are forbidden by God to eat from the tree of knowledge of good and evil.

In Genesis 3, a serpent tempts the woman:

And the serpent said unto the woman, Ye shall not surely die: For God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil.

— Genesis 3:4–5

Desiring this knowledge, the woman eats the forbidden fruit and gives some to the man, who also eats it. They become aware of their "nakedness" and make fig-leaf clothes, and hide themselves when God approaches. When confronted, Adam tells God that Eve gave him the fruit to eat, and Eve tells God that the serpent deceived her into eating it. God then curses the serpent, the woman, then the man, and expels the man and woman from the Garden before they ate of the tree of eternal life.

Quranic story

Further information: Adam in Islam

According to the Quran, Surah Al-A'raf 7:19 describes Adam and his wife in Paradise where they may eat what is provided, except for one Tree they must not eat from, lest they be considered Ẓālimūn (Arabic: ظالمون; wrongdoers).

Surah Al-A'raf 7:20–22 describes Shaitan (Arabic: شيطان), who whispers to Adam and his wife and deceives them. When they taste of the tree, their shame becomes manifest to them and they begin to cover themselves with leaves.

And their Lord called out to them: Did I not forbid you both from that tree and say to you that the Shaitan is your open enemy?

— Quran 7:22

Gnostic story

A Gnostic interpretation of the story proposes that it was the archons who created Adam and attempted to prevent him from eating the forbidden fruit in order to keep him in a state of ignorance, after the spiritual form of Eve entered the Tree of the Knowledge of Good and Evil while leaving a physical version of herself with Adam once she awakened him. But the forces of the heavenly realm (Pleroma) send the serpent as a representative of the divine sphere to reveal to Adam and Eve the evil intentions of their creators. The serpent succeeds in convincing them to eat the fruit and become like gods, capable of distinguishing between good and evil.

Identifications and depictions

The word fruit appears in Hebrew as פֶּ֫רִי (pərî ). As to which fruit may have been the forbidden fruit of the Garden of Eden, possibilities include apple, grape, pomegranate, fig, carob, etrog or citron, pear, quince, and mushrooms. The pseudepigraphic Book of Enoch describes the tree of knowledge: "It was like a species of the Tamarind tree, bearing fruit which resembled grapes extremely fine; and its fragrance extended to a considerable distance. I exclaimed, How beautiful is this tree, and how delightful is its appearance!" (1 Enoch 31:4).

In Islamic tradition, the fruit is commonly either identified with wheat or with grapevine.

Apple

See also: Apple (symbolism)

In Western Europe, the fruit was often depicted as an apple. This was possibly because of a misunderstanding of – or a pun on – two unrelated words mălum, a native Latin noun which means evil (from the adjective malus), and mālum, another Latin noun, borrowed from Greek μῆλον, which means apple. In the Vulgate, Genesis 2:17 describes the tree as de ligno autem scientiae boni et mali : "but of the tree [literally wood ] of knowledge of good and evil" (mali here is the genitive of malum). According to the Bible, there is nothing to show the forbidden fruit of the tree of knowledge was necessarily an apple.

The larynx, specifically the laryngeal prominence that joins the thyroid cartilage, in the human throat is noticeably more prominent in males and was consequently called an Adam's apple, from a notion that it was caused by the forbidden fruit getting stuck in Adam's throat as he swallowed it.

Grape

Rabbi Meir says that the fruit was a grape, made into wine. The Zohar explains similarly that Noah attempted (but failed) to rectify the sin of Adam by using grape wine for holy purposes. The midrash of Bereishit Rabah states that the fruit was grape, or squeezed grapes (perhaps alluding to wine). Chapter 4 of 3 Baruch, also known as the Greek Apocalypse of Baruch, designates the fruit as the grape. 3 Baruch is a first to third century text that is either Christian or Jewish with Christian interpolations.

Fig

See also: Figs in the Bible

The Bible states in the book of Genesis that Adam and Eve had made their own fig leaf clothing: "And the eyes of them both were opened, and they knew that they were naked; and they sewed fig-leaves together, and made themselves girdles". Rabbi Nehemiah Hayyun supports the idea that the fruit was a fig, as it was from fig leaves that God made garments for Adam and Eve upon expelling them from the Garden. "By that with which they were made low were they rectified." Since the fig is a long-standing symbol of female sexuality, it enjoyed a run as a favorite understudy to the apple as the forbidden fruit during the Italian Renaissance, Michelangelo Buonarroti depicting it as such in his masterpiece fresco on the Sistine Chapel ceiling.

Pomegranate

Proponents of the theory that the Garden of Eden was located somewhere in what is now known as the Middle East suggest that the fruit was actually a pomegranate, a plant indigenous from Iran to the Himalayas and cultivated since ancient times. The association of the pomegranate with knowledge of the underworld as provided in the Ancient Greek legend of Persephone may also have given rise to an association with knowledge of the otherworld, tying-in with knowledge that is forbidden to mortals. Also, it is believed Hades offered Persephone a pomegranate to force her to stay with him in the underworld. Hades is the Greek god of the underworld and the Bible states that whoever eats the forbidden fruit shall die.

Wheat

Rabbi Yehuda proposes that the fruit was wheat, because "a baby does not know to call its mother and father until it tastes the taste of grain."

In Hebrew, wheat is "khitah", which has been considered to be a pun on "khet", meaning "sin".

Although commonly confused with a seed, in the study of botany a wheat berry is technically a simple fruit known as a caryopsis, which has the same structure as an apple. Just as an apple is a fleshy fruit that contains seeds, a grain is a dry fruit that absorbs water and contains a seed. The confusion comes from the fact that the fruit of a grass happens to have a form similar to some seeds.

Mushroom

Plaincourault fresco, Garden of Eden.jpg

A fresco in the 13th-century Plaincourault Abbey in France depicts Adam and Eve in the Garden of Eden, flanking a Tree of Knowledge that has the appearance of a gigantic Amanita muscaria, a psychoactive mushroom. Terence McKenna proposed that the forbidden fruit was a reference to psychotropic plants and fungi, specifically psilocybin mushrooms, which he theorized played a central role in the evolution of the human brain. Earlier, in a well-documented but heavily criticized study, John M. Allegro proposed the mushroom as the forbidden fruit.

Banana

Several proponents of the theory exist dating from the thirteenth century. In Nathan HaMe’ati's 13th century translation of Maimonides's work The Medical Aphorisms of Moses, the banana is called the "apple of eden". In the sixteenth century, Menahem Lonzano considered it common knowledge in Syria and Egypt that the banana was the apple of Eden.

Coco de mer

Charles George Gordon identified the forbidden fruit of the tree of knowledge with the coco de mer.

Parallel concepts

Greek mythology

The similarities of the story to the story of Pandora's box were identified by early Christians such as Tertullian, Origen, and Gregory of Nazianzus.

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Tuesday, June 6, 2023

Eradication of suffering

From Wikipedia, the free encyclopedia

The eradication or abolition of suffering is the concept of using biotechnology to create a permanent absence of involuntary pain and suffering in all sentient beings.

Biology and medicine

The discovery of modern anesthesia in the 19th century was an early breakthrough in the elimination of pain during surgery, but acceptance was not universal. Some medical practitioners at the time believed that anesthesia was an artificial and harmful intervention in the body's natural response to injury. Opposition to anesthesia has since dissipated, however the prospect of eradicating pain raises similar concerns about interfering with life's natural functions.

People who are naturally incapable of feeling pain or unpleasant sensations due to rare conditions like pain asymbolia or congenital insensitivity to pain have been studied to discover the biological and genetic reasons for their pain-free lives. A Scottish woman with a previously unreported genetic mutation in a FAAH pseudogene (dubbed FAAH-OUT) with resultant elevated anandamide levels was reported in 2019 to be immune to anxiety, unable to experience fear, and insensitive to pain. The frequent burns and cuts she had due to her full hypoalgesia healed quicker than average.

In 1990, Medical Hypotheses published an article by L. S. Mancini on the "genetic engineering of a world without pain":

A hypothesis is presented to the effect that everything adaptive which is achievable with a mind capable of experiencing varying degrees of both pleasure and pain (the human condition as we know it) could be achieved with a mind capable of experiencing only varying degrees of pleasure.

The development of gene editing techniques like CRISPR has raised the prospect that "scientists can identify the causes of certain unusual people's physical superpowers and use gene editing to grant them to others." Geneticist George Church has commented on the potential future of replacing pain with a painless sensory system:

I imagine what this would be like on another planet and in the future, and... given that imagined future, whether we would be willing to come back to where we are now. Rather than saying whether we're willing to go forward... ask whether you're willing to come back.

Ethics and philosophy

Ethicists and philosophers in the schools of hedonism and utilitarianism, especially negative utilitarianism, have debated the merits of eradicating suffering. Transhumanist philosopher David Pearce, in The Hedonistic Imperative (1995), argues that the abolition of suffering is both technically feasible and an issue of moral urgency, stating that: "It is predicted that the world's last unpleasant experience will be a precisely dateable event."

The philosopher Nick Bostrom, director of the Future of Humanity Institute, advises a more cautious approach due to pain's function in protecting individuals from harm. However, Bostrom supports the core idea of using biotechnology to get rid of "a huge amount of unnecessary and undeserved suffering." It has also been argued that the eradication of suffering through biotechnology may bring about unwanted consequences, and arguments have been made that transhumanism is not the only philosophy worthy of consideration regarding the question of suffering — many people view suffering as one aspect in a dualist understanding of psychological and physical functioning, without which pleasure could not exist.

Animal welfare

In 2009, Adam Shriver suggested replacing animals in factory farming with genetically engineered animals with a reduced or absent capacity to suffer and feel pain. Shriver and McConnachie argued that people who wish to improve animal welfare should support gene editing in addition to plant-based diets and cultured meat.

Katrien Devolder and Matthias Eggel proposed gene editing research animals to remove pain and suffering. This would be an intermediate step towards eventually stopping all experimentation on animals and adopting alternatives.

Concerning wild-animal suffering, CRISPR-based gene drives have been suggested as a cost-effective way of spreading benign alleles in sexually reproducing species. To limit gene drives spreading indefinitely (for test programmes, for example), the Sculpting Evolution group at the MIT Media Lab developed a self-exhausting form of CRISPR-based gene drive called a "daisy-chain drive." For potential adverse effects of a gene drive, "[s]everal genetic mechanisms for limiting or eliminating gene drives have been proposed and/or developed, including synthetic resistance, reversal drives, and immunizing reversal drives."

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Sensory nervous system

From Wikipedia, the free encyclopedia
Sensory nervous system
Gray722.svg
Typical sensory system: the visual system, illustrated by the classic Gray's FIG. 722– This scheme shows the flow of information from the eyes to the central connections of the optic nerves and optic tracts, to the visual cortex. Area V1 is the region of the brain which is engaged in vision.
 
Details
Identifiers
Latinorgana sensuum
TA98A15.0.00.000
TA26729
FMA78499 75259, 78499

The visual system and the somatosensory system are active even during resting state fMRI
 
Activation and response in the sensory nervous system

The sensory nervous system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory neurons (including the sensory receptor cells), neural pathways, and parts of the brain involved in sensory perception and interoception. Commonly recognized sensory systems are those for vision, hearing, touch, taste, smell, balance and visceral sensation. Sense organs are transducers that convert data from the outer physical world to the realm of the mind where people interpret the information, creating their perception of the world around them.

The receptive field is the area of the body or environment to which a receptor organ and receptor cells respond. For instance, the part of the world an eye can see, is its receptive field; the light that each rod or cone can see, is its receptive field. Receptive fields have been identified for the visual system, auditory system and somatosensory system.

Stimulus

Organisms need information to solve at least three kinds of problems: (a) to maintain an appropriate environment, i.e., homeostasis; (b) to time activities (e.g., seasonal changes in behavior) or synchronize activities with those of conspecifics; and (c) to locate and respond to resources or threats (e.g., by moving towards resources or evading or attacking threats). Organisms also need to transmit information in order to influence another's behavior: to identify themselves, warn conspecifics of danger, coordinate activities, or deceive.

Sensory systems code for four aspects of a stimulus; type (modality), intensity, location, and duration. Arrival time of a sound pulse and phase differences of continuous sound are used for sound localization. Certain receptors are sensitive to certain types of stimuli (for example, different mechanoreceptors respond best to different kinds of touch stimuli, like sharp or blunt objects). Receptors send impulses in certain patterns to send information about the intensity of a stimulus (for example, how loud a sound is). The location of the receptor that is stimulated gives the brain information about the location of the stimulus (for example, stimulating a mechanoreceptor in a finger will send information to the brain about that finger). The duration of the stimulus (how long it lasts) is conveyed by firing patterns of receptors. These impulses are transmitted to the brain through afferent neurons.

Quiescent state

Most sensory systems have a quiescent state, that is, the state that a sensory system converges to when there is no input.

This is well-defined for a linear time-invariant system, whose input space is a vector space, and thus by definition has a point of zero. It is also well-defined for any passive sensory system, that is, a system that operates without needing input power. The quiescent state is the state the system converges to when there is no input power.

It is not always well-defined for nonlinear, nonpassive sensory organs, since they can't function without input energy. For example, a cochlea is not a passive organ, but actively vibrates its own sensory hairs to improve its sensitivity. This manifests as otoacoustic emissions in healthy ears, and tinnitus in pathological ears. There is still a quiescent state for the cochlea, since there is a well-defined mode of power input that it receives (vibratory energy on the eardrum), which provides an unambiguous definition of "zero input power".

Some sensory systems can have multiple quiescent states depending on its history, like flip-flops, and magnetic material with hysteresis. It can also adapt to different quiescent states. In complete darkness, the retinal cells become extremely sensitive, and there is noticeable "visual snow" caused by the retinal cells firing randomly without any light input. In brighter light, the retinal cells become a lot less sensitive, and consequently visual noise decreases.

Quiescent state is less well-defined when the sensory organ can be controlled by other systems, like a dog's ears that turn towards the front or the sides as the brain commands. Some spiders can use their nets as a large touch-organ, like weaving a skin for themselves. Even in the absence of anything falling on the net, hungry spiders may increase web thread tension, so as to respond promptly even to usually less noticeable, and less profitable prey, such as small fruit flies, creating two different "quiescent states" for the net.

Things become completely ill-defined for a system which connects its output to its own input, thus ever-moving without any external input. The prime example is the brain, with its default mode network.

Senses and receptors

While debate exists among neurologists as to the specific number of senses due to differing definitions of what constitutes a sense, Gautama Buddha and Aristotle classified five 'traditional' human senses which have become universally accepted: touch, taste, smell, sight, and hearing. Other senses that have been well-accepted in most mammals, including humans, include nociception, equilibrioception, kinaesthesia, and thermoception. Furthermore, some nonhuman animals have been shown to possess alternate senses, including magnetoreception and electroreception.

Receptors

Main article: sensory receptor

The initialization of sensation stems from the response of a specific receptor to a physical stimulus. The receptors which react to the stimulus and initiate the process of sensation are commonly characterized in four distinct categories: chemoreceptors, photoreceptors, mechanoreceptors, and thermoreceptors. All receptors receive distinct physical stimuli and transduce the signal into an electrical action potential. This action potential then travels along afferent neurons to specific brain regions where it is processed and interpreted.

Chemoreceptors

Main article: Chemoreceptor

Chemoreceptors, or chemosensors, detect certain chemical stimuli and transduce that signal into an electrical action potential. The two primary types of chemoreceptors are:

Photoreceptors

Main article: Photoreceptor cell

Photoreceptors are capable of phototransduction, a process which converts light (electromagnetic radiation) into, among other types of energy, a membrane potential. The three primary types of photoreceptors are: Cones are photoreceptors which respond significantly to color. In humans the three different types of cones correspond with a primary response to short wavelength (blue), medium wavelength (green), and long wavelength (yellow/red). Rods are photoreceptors which are very sensitive to the intensity of light, allowing for vision in dim lighting. The concentrations and ratio of rods to cones is strongly correlated with whether an animal is diurnal or nocturnal. In humans rods outnumber cones by approximately 20:1, while in nocturnal animals, such as the tawny owl, the ratio is closer to 1000:1. Ganglion Cells reside in the adrenal medulla and retina where they are involved in the sympathetic response. Of the ~1.3 million ganglion cells present in the retina, 1-2% are believed to be photosensitive ganglia. These photosensitive ganglia play a role in conscious vision for some animals, and are believed to do the same in humans.

Mechanoreceptors

Main article: Mechanoreceptor

Mechanoreceptors are sensory receptors which respond to mechanical forces, such as pressure or distortion. While mechanoreceptors are present in hair cells and play an integral role in the vestibular and auditory systems, the majority of mechanoreceptors are cutaneous and are grouped into four categories:

  • Slowly adapting type 1 receptors have small receptive fields and respond to static stimulation. These receptors are primarily used in the sensations of form and roughness.
  • Slowly adapting type 2 receptors have large receptive fields and respond to stretch. Similarly to type 1, they produce sustained responses to a continued stimuli.
  • Rapidly adapting receptors have small receptive fields and underlie the perception of slip.
  • Pacinian receptors have large receptive fields and are the predominant receptors for high-frequency vibration.

Thermoreceptors

Main article: Thermoreceptor

Thermoreceptors are sensory receptors which respond to varying temperatures. While the mechanisms through which these receptors operate is unclear, recent discoveries have shown that mammals have at least two distinct types of thermoreceptors:

TRPV1 is a heat-activated channel that acts as a small heat detecting thermometer in the membrane which begins the polarization of the neural fiber when exposed to changes in temperature. Ultimately, this allows us to detect ambient temperature in the warm/hot range. Similarly, the molecular cousin to TRPV1, TRPM8, is a cold-activated ion channel that responds to cold. Both cold and hot receptors are segregated by distinct subpopulations of sensory nerve fibers, which shows us that the information coming into the spinal cord is originally separate. Each sensory receptor has its own "labeled line" to convey a simple sensation experienced by the recipient. Ultimately, TRP channels act as thermosensors, channels that help us to detect changes in ambient temperatures.

Nociceptors

Main article: Nociceptor

Nociceptors respond to potentially damaging stimuli by sending signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain. They are found in internal organs, as well as on the surface of the body. Nociceptors detect different kinds of damaging stimuli or actual damage. Those that only respond when tissues are damaged are known as "sleeping" or "silent" nociceptors.

  • Thermal nociceptors are activated by noxious heat or cold at various temperatures.
  • Mechanical nociceptors respond to excess pressure or mechanical deformation.
  • Chemical nociceptors respond to a wide variety of chemicals, some of which are signs of tissue damage. They are involved in the detection of some spices in food.

Sensory cortex

All stimuli received by the receptors listed above are transduced to an action potential, which is carried along one or more afferent neurons towards a specific area of the brain. While the term sensory cortex is often used informally to refer to the somatosensory cortex, the term more accurately refers to the multiple areas of the brain at which senses are received to be processed. For the five traditional senses in humans, this includes the primary and secondary cortices of the different senses: the somatosensory cortex, the visual cortex, the auditory cortex, the primary olfactory cortex, and the gustatory cortex. Other modalities have corresponding sensory cortex areas as well, including the vestibular cortex for the sense of balance.

Somatosensory cortex

Located in the parietal lobe, the primary somatosensory cortex is the primary receptive area for the sense of touch and proprioception in the somatosensory system. This cortex is further divided into Brodmann areas 1, 2, and 3. Brodmann area 3 is considered the primary processing center of the somatosensory cortex as it receives significantly more input from the thalamus, has neurons highly responsive to somatosensory stimuli, and can evoke somatic sensations through electrical stimulation. Areas 1 and 2 receive most of their input from area 3. There are also pathways for proprioception (via the cerebellum), and motor control (via Brodmann area 4). See also: S2 Secondary somatosensory cortex.

The human eye is the first element of a sensory system: in this case, vision, for the visual system.

Visual cortex

The visual cortex refers to the primary visual cortex, labeled V1 or Brodmann area 17, as well as the extrastriate visual cortical areas V2-V5. Located in the occipital lobe, V1 acts as the primary relay station for visual input, transmitting information to two primary pathways labeled the dorsal and ventral streams. The dorsal stream includes areas V2 and V5, and is used in interpreting visual 'where' and 'how.' The ventral stream includes areas V2 and V4, and is used in interpreting 'what.' Increases in Task-negative activity are observed in the ventral attention network, after abrupt changes in sensory stimuli, at the onset and offset of task blocks, and at the end of a completed trial.

Ear

Auditory cortex

Located in the temporal lobe, the auditory cortex is the primary receptive area for sound information. The auditory cortex is composed of Brodmann areas 41 and 42, also known as the anterior transverse temporal area 41 and the posterior transverse temporal area 42, respectively. Both areas act similarly and are integral in receiving and processing the signals transmitted from auditory receptors.

Nose

Primary olfactory cortex

Located in the temporal lobe, the primary olfactory cortex is the primary receptive area for olfaction, or smell. Unique to the olfactory and gustatory systems, at least in mammals, is the implementation of both peripheral and central mechanisms of action. The peripheral mechanisms involve olfactory receptor neurons which transduce a chemical signal along the olfactory nerve, which terminates in the olfactory bulb. The chemoreceptors in the receptor neurons that start the signal cascade are G protein-coupled receptors. The central mechanisms include the convergence of olfactory nerve axons into glomeruli in the olfactory bulb, where the signal is then transmitted to the anterior olfactory nucleus, the piriform cortex, the medial amygdala, and the entorhinal cortex, all of which make up the primary olfactory cortex.

In contrast to vision and hearing, the olfactory bulbs are not cross-hemispheric; the right bulb connects to the right hemisphere and the left bulb connects to the left hemisphere.

Tongue

Gustatory cortex

The gustatory cortex is the primary receptive area for taste. The word taste is used in a technical sense to refer specifically to sensations coming from taste buds on the tongue. The five qualities of taste detected by the tongue include sourness, bitterness, sweetness, saltiness, and the protein taste quality, called umami. In contrast, the term flavor refers to the experience generated through integration of taste with smell and tactile information. The gustatory cortex consists of two primary structures: the anterior insula, located on the insular lobe, and the frontal operculum, located on the frontal lobe. Similarly to the olfactory cortex, the gustatory pathway operates through both peripheral and central mechanisms. Peripheral taste receptors, located on the tongue, soft palate, pharynx, and esophagus, transmit the received signal to primary sensory axons, where the signal is projected to the nucleus of the solitary tract in the medulla, or the gustatory nucleus of the solitary tract complex. The signal is then transmitted to the thalamus, which in turn projects the signal to several regions of the neocortex, including the gustatory cortex.

The neural processing of taste is affected at nearly every stage of processing by concurrent somatosensory information from the tongue, that is, mouthfeel. Scent, in contrast, is not combined with taste to create flavor until higher cortical processing regions, such as the insula and orbitofrontal cortex.

Human sensory system

The human sensory system consists of the following subsystems:

Diseases

Disability-adjusted life year for sense organ diseases per 100,000 inhabitants in 2002.
  no data
  less than 200
  200-400
  400-600
  600-800
  800-1000
  1000-1200
  1200-1400
  1400-1600
  1600-1800
  1800-2000
  2000-2300
  more than 2300
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