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The cat's tongue is covered with pointed spines facing the back, called papillae, whose precise function is a mystery. In a study both experimental and theoretical, researchers at the Georgia Institute of Technology have explored how cats care for fur with the help of these fine structures.
Doctors Noel and Hu discover structures on the cat's tongue, hollow thorns that they call cavo papillae, spread over six species of cats. Image credit: Pavel Kessa.
Domestic cats, who sleep an average of 14 hours a day, spend up to a quarter of their waking hours grooming, eliminating fleas, debris and excessive heat from the fur.
The cat's tongue is lined with hundreds of sharp spines, composed of keratin and activating their action during grooming.
"The cat's tongue is best known for its hundreds of sharp, backward-facing keratin spines, called filiform papillae," said Georgia Tech scientists Alexis Noel and David Hu.
"A 1982 study concluded that a cat papilla had the shape of a solid cone, an observation that remained uncontested for two decades."
"In our study, we show that the disc is actually shovel-shaped, which allows it to use surface tension forces to absorb saliva."
Kinematics of cat grooming: (A) a domestic cat makes his toilet; (B) a close-up view of his tongue showing the anisotropic papillae, which point to the left towards the throat; (C) the four phases of cat grooming; (D and E) thermal images of a cat grooming himself; the white colors are the warmest and the dark blue colors are the coldest, as indicated by the legend on the right; during the groom (D), the fur is separated by the movement of the tongue, exposing the skin; the heat of the tongue and skin is indicated by the color white; after the groom (E), evaporation causes a temperature drop of 17 degrees Celsius, as indicated by dark purple. Image credit: Noel & Hu, doi: 10.1073 / pnas.1809544115.
Researchers used high-speed video, CT scans and grooming force measurements to explore how the taste buds make it easier to groom the tongue tissues of six species of cats: domestic cat, bobcat, cougar, leopard snow, tiger and lion.
Experiments revealed that the U-shaped hollows at the top of the papillae evacuated saliva from the mouth, with each absorbing action capturing up to 4.1 μL of saliva, being the equivalent of one. tenth of the drop of a typical pipette.
Each licking of the tongue deposits about 50% of the liquid on the tongue on the coat and can provide a significant fraction of the cooling effect necessary for the regulation of body temperature.
In addition, the ease of grooming depends on the ability of the taste buds to penetrate the fur, which is why some types of domestic cats, such as long-haired Persian cats, are covered with a fur that easily braids and which is notoriously difficult to groom.
With the help of this information, the team has developed a hair brush inspired by the tongue of a cat, easier to clean than human hair brushes.
"A biologically inspired hairbrush could prove to be a handy tool for removing allergens from cat fur and applying cleansing lotions and medications on cat skin," said Dr. Noel and Dr. Dr. Hu.
The study is published in Proceedings of the National Academy of Sciences.
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Alexis C. Noel and David L. Hu. Cats use hollow taste buds to absorb fur saliva. PNAS, published online November 19, 2018; doi: 10.1073 / pnas.1809544115
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