What is the vomeronasal organ (also known as Jacobson’s Organ) in cats?

Also known as the Jacobson’s organ, the vomeronasal organ (VNO) is a chemosensory tubular organ located between the hard palate of the mouth and the soft tissue of the nasal septum.

The vomeronasal organ is an accessory olfactory system, best described as a taste-smell organ. It is used to identify non-volatile chemicals known as pheromones primarily from other cats but also from prey and predators. Pheromones in glandular secretions and urine advertise important information such as territorial boundaries, dominance and reproductive status. Scent glands on the head and face of cats produce feline facial pheromones which induce a sense of calm. Urine spraying marks a cat’s territory and is most common in entire male cats.

Danish anatomist Ludwig Levin Jacobson discovered the vomeronasal organ in 1811.

Flehmen response

The flehmen response (also referred to as stink face by cat lovers) occurs when a cat encounters a pheromone. Curling the upper lip and exposing the teeth transfers the pheromones into the mouth. Once inside, the tongue flicks the scent upwards to the incisive papilla (often mislabelled as the vomeronasal organ), a small fleshy structure located above the upper incisors. The incisive papilla connects the oral cavity with the vomeronasal organ via the incisive duct which contains fluid-filled incisive (nasopalatine) canals (NPC).

Specialised sensory receptor neurons with axons (a long slender projection) travel to the accessory olfactory bulb (also known as the vomeronasal bulb). Sensory receptor neurons contain microvilli with sensory receptors (also known as pheromone receptors) which bind to incoming pheromones. Sensory receptor neurons recognise pheromones involved in initiating a behavioural response. VNO signalling leads to activation of the hypothalamus by the way of the accessory olfactory bulb and amygdala thereby contributing to the regulation of reproductive, defensive, and ingestive behaviour, and neuroendocrine secretion.

Do humans have a vomeronasal organ?

Humans used to have a vomeronasal organ, however, it is no longer operational. Dogs, horses, pigs, goats, giraffes, elephants, amphibians, rodents, possums, and new world monkeys. Humans rely on sight more than other senses.