Micron-sized hair cells in the inner ears of animals may function as reliable biological compass needles, suggests recent study published in the European Physical Journal Special Topics. The discovery supports one of the main hypotheses of how animals can use the Earth’s magnetic field as a source of locational information.
The sixth sense, magnetoreception, has remained one of sensory scientists’ greatest mysteries up until now.
One hundred ‘special’ hair cells are required to perceive the Earth’s magnetic field, proving 1 of 2 magnetoreception theories.
Dr. Kirill Kavokin of St. Petersburg State University in Russia used statistical analysis to show that animals use about 100 of these hair cells to sense the Earth’s magnetic field. The intriguing finding may help biologists better comprehend the origins of magnetoreception and finally identify mechanisms underlying this characteristic.
One of the two dominant theories of magnetoreception is supported by the current research. This is the presence of “stereocilia”, which are bundles of hair cells in the inner ear. The scientists propose that the magnetite nanocrystals are attached to the stereocilia. Because this iron-based mineral can be permanently magnetized, it aligns itself with the Earth’s magnetic field. When the animal’s orientation changes, the magnetite forces change the orientation of the attached stereocilia.
That’s not all, either. The notion is also based on how changes in stereocilia orientation are detected by mechanoreceptors, or nerve cells, which can sense mechanical pressure. The animal is given a physical sensation of a magnetic field in this way. It has not been known until now if these nerve cells are sensitive enough to notice such subtle changes.
In the new study, Kavokin employed statistics to used the stereocilia fluctuations and show that these microstructures could actually function as vulnerably sensitive compass needles. The researcher also assigned a number to how many of these structures are required for mechanoreceptors to detect their fluctuations in order to take things a step further (i.e., 100).
The list of animals that use magnetoreception to navigate is vast
There are a large number of creatures that use magnetoreception to navigate, despite the mystery surrounding how they can detect the Earth’s magnetic field. Consider the loggerhead sea turtles as adults, which use their highly developed magnetic sense to return to-their breeding grounds.
There is evidence that homing pigeons navigate themselves home using a variety of biological compasses in coordination with the Earth’s magnetic field.
In a previous article, we talked about a study that claimed that humans also have a biological sense of the Earth’s magnetic field. Human brains were shown to gather and process directional input from magnetic field receptors when subjects were placed in a “faraday cage” with a magnetic field.
That being said, there is still a lot to learn about the processes of magnetoreception, and does not emphasize much about the limitations of the study.
Nevertheless, it will always be interesting to see how sensory biologists explore this incredible evolutionary ability to navigate and survive as they continue to scratch the surface (and their heads!).