It is a common fact that humans possess five senses; however, this notion has changed with the advancement in science and technology. Humans have another sense called proprioception, which can be described as the “awareness” of the limbs and body in space. When the police ask an inebriated person to touch their nose, they are essentially testing their sense of proprioception. It is also responsible for balance and spatial awareness of the body.
Backed by Evidence
Research has shown that a gene, PIEZO2, may play a pivotal role in this sense. This gene is associated with feeling a sense of pressure (Mechanosensation). In other words, if someone were to push down on their skin, they would feel that as pressure. A study that involved two young subjects with mutations to the aforementioned genes was performed. The test required the subjects to reach out for an object in front of them; first with their eyes open and then, with a blindfold. Compared to the people who did not have a mutation of this gene, the subjects had a harder time reaching for the object while blindfolded. Similarly, when the subjects were asked to walk blindfolded, they had found it considerably more difficult than the people who did not have a mutation on this gene.
Organs for Proprioception
The human body comprises many organs, but the functions of most are somewhat obscure. Proprioception is mediated by special receptors and sensory neurons located within the muscles, tendons and joints. These structures encode various information, such as the velocity of the limb, limb load, and limb limits. What is even more impressive is the fact that terrestrial plants (most notably flowering plants) are also known to exhibit this phenomenon.
Sixth Sense in Other Organisms.
Invertebrates have a special fluid-filled organ for perception of gravity. This organ is called the statocyst. This is essentially a fluid-filled chamber that has minute, sensitive hairs lining its walls. It also contains tiny stone-like grains called statoliths. Depending on the animal, these statoliths may be fixed loosely to the sensitive hairs or be free-moving. When the animal changes orientation or position, information about the same is conveyed to the sense-hairs by the statolith’s pressure.
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