vibrissae

Vibrissae, commonly called whiskers, are long, stiff tactile hairs found on many mammals. They are specialized hairs anchored in deeply situated follicles that contain a large blood sinus and dense nerve endings, making them among the most sensitive tactile sensors in the skin.

Location and structure: Vibrissae occur in distinct facial groups, especially the mystacial whiskers on the upper muzzle and the genal whiskers along the cheeks; some species also have supraorbital or chin whiskers. Each hair grows from a follicle-sinus complex, a specialized unit that includes a blood sinus, connective tissue, and rich innervation. The follicles are capable of being moved by small facial muscles, a behavior known as whisking, which actively positions the whiskers for sampling the environment.

Function and processing: Deflection of a vibrissa deforms mechanoreceptors in the follicle-sinus complex and transmits tactile information via the trigeminal nerve to brain regions involved in sensory processing. In many animals, the brain contains a detailed map of vibrissae, exemplified by the barrel cortex in rodents, supporting high-resolution tactile perception.

Role and variation: Vibrissae help detect contact with objects, determine object location and shape, and sense air currents around obstacles, aiding navigation in darkness or clutter. Hydrodynamic sensing is observed in some aquatic mammals. In humans, vibrissae are greatly reduced and have limited tactile function compared with other mammals.

Evolution and study: The vibrissal system is a prominent model in neuroscience for active sensing and somatosensory processing, illustrating how animals use tactile input to guide behavior.