A cat usually lands on its feet regardless of the position from which it is dropped. A slow-motion film of a cat falling shows that the upper half of its body twists in one direction while the lower half twists in the opposite direction. (See figure below.) Why does this type of rotation occur?
The rotation of the cat's body during a fall is a result of a phenomenon called the "righting reflex." This reflex is a combination of the cat's flexible spine, inner ear balance organs, and specialized muscles. It allows the cat to adjust its body position in mid-air to land on its feet.
To understand this rotation, let's break it down step by step:
1. Initial Orientation: When a cat is dropped or falls, it initially extends its front and hind legs outward, spreading them apart. This helps create a larger surface area to help control its descent. At this stage, the cat's body is aligned in a more parallel position to the ground.
2. Twisting Motion: As the cat starts to fall, its flexible spine comes into play. The cat begins to twist its upper body in one direction while simultaneously twisting its lower body in the opposite direction. This twisting motion is known as the "righting reflex."
3. Counter-rotation: The cat's inner ear balance organs, specifically the semicircular canals, detect the change in the orientation of the body. In response, the cat's brain sends signals to its muscles to counter-rotate the body segments. The upper body rotates in one direction, while the lower body rotates in the opposite direction, creating the twisting motion.
4. Alignment: By twisting its body segments in opposite directions, the cat creates a torque force that allows it to reorient itself in mid-air. As the upper body twists in one direction, the hind limbs follow, aligning with it. Simultaneously, the lower body twists in the opposite direction, causing the front limbs to rotate and align with it. This realignment helps the cat to land on its feet.
The righting reflex is instinctual and enables cats to land safely in most situations. However, it's important to note that the righting reflex requires a certain minimum height in order for the cat to have enough time to adjust its body position. Additionally, factors like the surface on which the cat lands, the cat's health and age, and other variables can affect the cat's ability to land safely.