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Magnetoception

Magnetoception

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Magnetoception is the ability to detect a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 to perceive direction, altitude or location. This sense
Sense
Senses are physiological capacities of organisms that provide inputs for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception...

 plays a role in the navigational abilities of several animal species and has been postulated as a method for animals to develop regional maps.

Magnetoception is most commonly observed in bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, where sensing of the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

 is important to the navigational abilities during migration
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...

; it has also been observed in bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

, fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

, insects (including fruit flies
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

 and honeybees), and animals such as turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

s, lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...

s, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s and stingray
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...

s.

Mechanisms


The phenomenon is poorly understood, and there exist two main hypotheses to explain magnetoception.

In pigeons and other birds, researchers have identified a small heavily innervated region of the upper beak which contains biological magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

 and is believed to be involved in magnetoception.

Evidence has also been found that the light-sensitive molecule cryptochrome
Cryptochrome
Cryptochromes are a class of blue light-sensitive flavoproteins found in plants and animals. Cryptochromes are involved in the circadian rhythms of plants and animals, and in the sensing of magnetic fields in a number of species...

 in the photoreceptor cells of the eyes is involved in magnetoception.
According to one model, cryptochrome when exposed to blue light becomes activated to form a pair of two radical
Radical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...

s (molecules with a single unpaired electron) where the spin
Spin (physics)
In quantum mechanics and particle physics, spin is a fundamental characteristic property of elementary particles, composite particles , and atomic nuclei.It is worth noting that the intrinsic property of subatomic particles called spin and discussed in this article, is related in some small ways,...

s of the two unpaired electrons are correlated. The surrounding magnetic field affects the kind of this correlation (parallel or anti-parallel), and this in turn affects the length of time cryptochrome stays in its activated state. Activation of cryptochrome may affect the light-sensitivity of retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

l neurons, with the overall result that the bird can "see" the magnetic field. Cryptochromes are also essential for the light-dependent ability of the fruit fly Drosophila melanogaster
Drosophila melanogaster
Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting from Charles W...

to sense magnetic fields.

It is believed that birds use both the magnetite-based and the radical pair-based approach, "with the radical pair mechanism in the right eye providing directional information and a magnetite-based mechanism in the upper beak providing information on position as component of the 'map'".

There are, however, two types of magnetic sensing mechanisms that have been more thoroughly described. The first is the inductive sensing methods used by sharks, stingrays and chimaera
Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...

s (cartilaginous fish). These species possess a unique electroreceptive
Electroreception
Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed only in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation and for electrocommunication.- Overview :Electroreception is...

 organ known as ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...

which can detect a slight variation in electric potential. These organs are made up of mucus-filled canals that connect from the skin's pores to small sacs within the animal's flesh that are also filled with mucus. The sensing method of these organs is based on Faraday's law
Faraday's law of induction
Faraday's law of induction dates from the 1830s, and is a basic law of electromagnetism relating to the operating principles of transformers, inductors, and many types of electrical motors and generators...

; a time-varying magnetic field moving through a conductor creates an electric potential across the ends of the conductor. In this case the conductor is the animal moving through a magnetic field, and the potential induced depends on the time varying rate of flux through the conductor according to
.

These organs detect very small fluctuations in the potential difference between the pore and the base of the electroreceptor sack. An increase in potential results in a decrease in the rate of nerve activity, and a decrease in potential results in an increase in the rate of nerve activity. This is analogous to the behavior of a current carrying conductor; with a fixed channel resistance, an increase in potential would decrease the amount of current detected, and vice versa. These receptors are located along the mouth and nose of sharks and stingrays.

The second known method of magnetic sensing, or magnetoception, is found in a class of bacteria known as magnetotactic bacteria
Magnetotactic bacteria
Magnetotactic bacteria are a polyphyletic group of bacteria discovered by Richard P. Blakemore in 1975, that orient along the magnetic field lines of Earth's magnetic field. To perform this task, these bacteria have organelles called magnetosomes that contain magnetic crystals...

. These bacteria demonstrate a phenomenal behaviorism known as magnetotaxis
Magnetotaxis
Logically, magnetotaxis describes an ability to sense a magnetic field and coordinate movement in response. It was applied to the behavior of certain motile, aquatic bacteria in 1975 by R. P. Blakemore....

, in which the bacteria orients itself and migrates in the direction along the Earth's magnetic field lines. The bacteria contain magnetosome
Magnetosome
Magnetosome chains are membranous prokaryotic organelles present in magnetotactic bacteria. They contain 15 to 20 magnetite crystals that together act like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic...

s, which are particles of magnetite or iron sulfide enclosed within the bacteria cells. Each bacterium cell essentially acts as a magnetic dipole. They form in chains where the moments of each magnetosome align in parallel, giving the bacteria its permanent-magnet characteristics. These chains are formed symmetrically to preserve the crystalline structure of the cells. These bacteria are said to have permanent magnetic sensitivity.

In humans


Magnetic bones have been found in the human nose, specifically the sphenoidal/ethmoid sinus
Ethmoid sinus
The ethmoid sinus is each of the two paranasal sinuses within the ethmoid bone, comprising the ethmoidal air cells and filled with air. These are divided into anterior, middle and posterior group. The ethmoidal air cells consist of numerous thin-walled cavities situated in the ethmoidal labyrinth...

es Beginning in the late 1970s, the group of Robin Baker
Dr Robin Baker
Robin Baker is a British novelist, popular science writer, lecturer and broadcaster. A best-selling author in the field of sexual biology his books have been translated into 27 different languages. These include the international bestseller Sperm Wars which was based on his own lab’s original...

 at the University of Manchester
University of Manchester
The University of Manchester is a public research university located in Manchester, United Kingdom. It is a "red brick" university and a member of the Russell Group of research-intensive British universities and the N8 Group...

 began to conduct experiments that purported to exhibit magnetoception in humans: people were disoriented and then asked about certain directions; their answers were more accurate if there was no magnet attached to their head. Other scientists have maintained they could not reproduce these results though the evidence from both sides remains contentious. A 2007 study found some other evidence for human magnetoception has been put forward: low-frequency magnetic fields can produce an evoked response in the brains of human subjects.

Magnetoception in humans has also been achieved by magnetic implants  and by non-permanently attached artificial sensory "organs".

Additionally, a magnetosensitive protein, cryptochrome-2
Cryptochrome
Cryptochromes are a class of blue light-sensitive flavoproteins found in plants and animals. Cryptochromes are involved in the circadian rhythms of plants and animals, and in the sensing of magnetic fields in a number of species...

, has been found in the human eye.

Other organisms


In bees, it has been observed that magnetite is embedded across the cellular membrane of a small group of neurons; it is thought that when the magnetite aligns with the Earth's magnetic field, induction
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....

 causes a current to cross the membrane which depolarizes
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...

 the cell.

Crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...

s are believed to have magnetoception, which allows them to find their native area even after being moved hundreds of miles away. Some have been strapped with magnets to disorient them and keep them out of residential areas.

In 2008, a research team led by Hynek Burda using Google Earth
Google Earth
Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...

 accidentally discovered that magnetic fields affect the body orientation of cows and deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...

 during grazing
Grazing
Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...

 or resting. In a followup study in 2009, Burda and Sabine Begall observed that magnetic fields generated by power lines disrupted the orientation of cows from the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

.

Certain types of bacteria (magnetotactic bacteria
Magnetotactic bacteria
Magnetotactic bacteria are a polyphyletic group of bacteria discovered by Richard P. Blakemore in 1975, that orient along the magnetic field lines of Earth's magnetic field. To perform this task, these bacteria have organelles called magnetosomes that contain magnetic crystals...

) and fungi are also known to sense the magnetic flux direction; they have organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....

s known as magnetosome
Magnetosome
Magnetosome chains are membranous prokaryotic organelles present in magnetotactic bacteria. They contain 15 to 20 magnetite crystals that together act like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilic...

s containing magnetic crystals for this purpose.

Some migratory bird species, specifically European robins
European Robin
The European Robin , most commonly known in Anglophone Europe simply as the Robin, is a small insectivorous passerine bird that was formerly classed as a member of the thrush family , but is now considered to be an Old World flycatcher...

, have shown behavioral evidence of having a magnetic inclination compass. This was first realized by the unusual behavior of birds in captivity during their natural migratory seasons. The birds tended to position themselves at the location within their cage that corresponded with the direction of their instinctive migration path. Experiments were conducted in which the orientation of the Earth's field was distorted with an applied external field. The applied field was controlled such that only the horizontal or vertical component of the Earth's field was reversed (by applying a field twice as strong and opposite in direction). The intensity and inclination angle of the applied field was kept equal to the Earth's natural field as measured at the location of the experiment. It was found that Robins are sensitive to both the horizontal and vertical components of the Earth's field; reversing either component (individually) resulted in disorientation of the birds. However, when both components were reversed simultaneously, the equivalent of changing the magnetic polarity of the earth, had no effect on their orientation. Thus, the Robins can determine whether they are flying poleward or equator-ward based on the inclination angle of the Earth's field with respect to their normal [to the ground], or vertical direction. However, they cannot determine the difference in the magnetic polarity of the present field. This explains the basis for naming their sensing method an inclination compass as opposed to the standard compass we are used to.

Spiny lobster
Spiny lobster
Spiny lobsters, also known as langouste or rock lobsters, are a family of about 45 species of achelate crustaceans, in the Decapoda Reptantia...

s have shown evidence of having a magnetic polarity compass. They are sensitive only to the horizontal component of the magnetic field, and the vertical component has no effect on their behavior. By sensing the horizontal component only, they can sense the polarity of the magnetic field. This is opposite the effect of the inclination compass found in birds, where reversing the vertical or horizontal component was equally effective in disorientating them.

Some species of sea turtle
Sea turtle
Sea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...

s have utilized the Earth's magnetic field for directional orientation. Loggerhead
Loggerhead Sea Turtle
The loggerhead sea turtle , or loggerhead, is an oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around long when fully grown, although larger specimens of up to have been discovered...

 and leatherback sea turtles have been studied and show orientating abilities based on both lighting clues and the surrounding magnetic field.