Cats, as we all know from watching the tom next door effortlessly negotiate the length of the garden fence, have a wonderful sense of balance. The main reason for this is the speed of the cat's muscle reaction to remarkably fast messages sent from the eyes and balancing organs in the inner ear by way of the rain. The animal is ultrasensitive to changes in its position, and communicates any alteration to the muscle and joints far faster than a human being.
The Use of The Tail
It is thought that the cat's tail acts as a counter-balance in much the same way that a tightrope walker uses a long pole. The principle is simple: for example, if a cat is walking along a narrow wall or fence and decides to peer over in one direction, thereby shifting its centre of gravity, it will automatically move its tail in the opposite direction, re-establishing its body's centre of gravity and keeping itself from falling off.
The tail also acts as a counter weight when the cat is making quick turns while running at high speed. Watch a cheetah going flat out after a zig-zagging gazelle. At each turn, the tail is swung away from the direction pf the body to give split-second stability on the "cornering". It seems logical that the cheetah, the champion sprinter among cats, should have such a long tail.
When jumping, a cat's tail is often said to act as a sort of rudder, but it is nevertheless true that cats with very short tails like lynxes or manx cats still jump exceedingly well.
The Art of Falling
When a cat falls through the air, its eyes can specialized structures within the inner ear transmit information to the brain on the position of the head in relation to the ground. As the head changes position or is subjected to changes in acceleration, crystals and liquid inside the inner ear and affected, and this movement is detected by sensitive hairs. In milli-seconds, the brain receives the signal and sends ultra-fast nerve commands to the head to put it "square" with the ground. The rest of the body aligns with the head, and the cat ends up in a position perfectly prepared for landing.
A newborn kitten is born with the inner ear mechanism fully developed, but because its eyes haven't yet opened, it can not see. Since perfect balance requires a combination of eye and inner ear messages, a kitten's righting reflex isn't operational until its eyes open.
Recently it has been found that cats that fall from tall buildings don't suffer injuries in exactly the way you might expect. As you would predict, the rate of cat injuries increases steadily the higher the storey from which the animal falls - up to seven storeys in height. But above that height the rate of fractures inflicted actually decreases! The reason for this appears to be that, after falling for a distance of about five storeys, the average-sized cat reaches maximum speed, the so-called terminal velocity of a falling body. At this point the cat's inner ear system is no longer stimulated by acceleration and the speed is constant. The cat therefore relaxes and spreads its legs to that its body and limbs take advantage of maximum air resistance - much in the same way that a freefall parachutist stabilizes his descent.
Relaxed limbs are less likely to fracture so, strange as it may seem, a cat falling from a ten-storey-high window ledge may well fare better than one tumbling a mere three storeys. (Please do not try to prove what I say bu experimenting with your pet!) I well recall incidents of this kind happening when I was a student in Glasgow. In the summer, cats would bask on the narrow window ledges of the old tenements (apartment blocks), until the owners closed the windows and unwittingly launched the cats into space. They would fall distances of two to five storeys, and many of them survived the descent and landed in the correct position . However, because cats have relatively weak neck muscles, they could not hold back their head, so their chins hit the ground with some force. One of my commonest accident cases in those summer days was to treat the midline fractures of the lower jaw that resulted.