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CHEMICAL SPIN. “These properties of the avian magnetic compass remained enigmatic until the Radical Pair Model provided a possible explanation. The model, described in detail by Ritz et al. proposes that the avian magnetic compass is based on spin-chemical processes in specialized photopigments.” http://rsif.royalsocietypublishing.org/content/12/103/20141103.full View in LinkedIn

STELLAR VS COMPASS. “The brain region Cluster N is necessary for magnetic compass orientation behavior, but not for star and Sun compass orientation. The trigeminal nerve is neither necessary nor sufficient for magnetic compass orientation in European robins.” https://lnkd.in/eUbuD-a View in LinkedIn

TWO MECHANISMS. “On the basis of current scientific evidence, iron-mineral-based magnetoreception and radical-pair-based magnetoreception mechanisms seem to exist in birds, but they seem to be used for different purposes.” https://lnkd.in/eUbuD-a View in LinkedIn

QUANTUM CHEMISTRY. “A light-sensitive molecule (D) absorbs light and uses the light energy to transfer an electron to an acceptor (A); thereby, a radical pair is produced. If this radical pair is long-lived (>1 μs), then it can, depending on the spin of the electrons, exist in one of two states—a singlet state (spins antiparallel) or a triplet state (spins parallel). It is known from chemistry that singlet and triplet states have different chemical properties; thus, they often result in different chemical end products. Earth-strength magnetic fields can theoretically affect this statistical equilibrium and thereby modulate a presently unknown biochemical pathway.” https://lnkd.in/eUbuD-a View in LinkedIn

WEAK SIGNAL. “It is very challenging to sense magnetic fields as weak as that of the Earth using only biologically available materials. Only two basic mechanisms are considered theoretically viable in terrestrial animals: iron-mineral-based magnetoreception and radical-pair based magnetoreception.” https://lnkd.in/eUbuD-a View in LinkedIn

STRUCTURAL COMPASS. “The magnetic compass behavior of newts and birds is dependent on the wavelengths of light being available during behavioral tests; theoretical considerations led Klaus Schulten to suggest that chemical reactions in photosensitive molecules could form the basis of a magnetic compass sense.” https://lnkd.in/eUbuD-a View in LinkedIn

FUNCTIONAL TEST. “Light-dependent magnetic compass information is transmitted from the retina through the optic nerve to the visual thalamus and from there to Cluster N in the forebrain via the thalamofugal visual pathway. If Cluster N is destroyed, European robins can no longer use their magnetic compass.” https://lnkd.in/eUbuD-a View in LinkedIn

RADICAL PAIRS. “The reference direction provided by the Earth’s magnetic field is detected in the birds’ eyes, where cryptochrome proteins are the most likely light-dependent magnetic sensory molecules. Light absorption is thought to generate long-lived flavin-tryptophan radical pairs within cryptochromes in the retina, the reaction yields of which are determined by the orientation of the molecule with respect to the geomagnetic field vector.” https://lnkd.in/eUbuD-a View in LinkedIn

BIRD STRUCTURE. “These findings have since sparked a search for putative magnetoreceptors in the inner ear of birds. Using correlative light and electron microscopy, a previously undescribed iron-rich organelle has been discovered in the cuticular plate of avian hair cells. The organelle ranges from 300 to 600 nm in size and is comprised of ferritin-like granules. The structure is conspicuous given that almost 100% of hair cells contain only a single iron-rich organelle and seems to be limited to birds.” http://rsif.royalsocietypublishing.org/content/12/110/20150499.full View in LinkedIn

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