Vibrissae

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This article is about vibrissae, often called whiskers. For other uses of the word whisker, see whisker.

Vibrissae (singular: vibrissa) are hairs, usually specialized for tactile sensation, that grow around the nostrils or other parts of the face in most mammals. In addition to the facial area, they can also be found on the wrists of the forelegs of cats. They are usually thicker and stiffer than other types of hair. The term is also used in reference to the stiff feathers near the mouths of some birds.

Vibrissae consist of inert material and contain no nerves. What makes vibrissae different from other hairs is that they are implanted in a special follicle sealed by a capsule of blood, called a blood sinus. Touching a vibrissa causes it to bend and the blood in the sinus is pushed to one side or the other. The blood amplifies the movement and allows the nerves at the base to detect extremely small deflections. In some mammals, the follicles of vibrissae are surrounded by a highly developed sheath of muscle tissue which can be used to move the whiskers. Whiskers can grow extremely long; the whiskers of a chinchilla can be up to a third of its body length.

Vibrissae offer an advantage to animals that do not always have sight to rely on to navigate, or to find food, or when the usefulness of non-tactile senses is limited. Some animals, such as house mice, can detect air movements with their vibrissae. A large part of the brain of many mammals is devoted to processing the nerve impulses from vibrissae because it is important to their survival. Mammals use a great deal of energy to keep the follicles housing their whiskers warm and ready to use.