a cat sniffing the air with open mouth, using her jacobson's (vomeronasal) organ

Anatomy of the Jacobson’s (vomeronasal) organ

Surely you have seen the stink face on cats before – a snapshot of what they look like when using their Jacobson’s organ. This behavior is called Flehmen or Flehmen response. If you are interested in what that is and how it works, keep reading.

The functional significance of Jacobson’s organ

Pheromone detection with the Flehmen response

Cats use the Flehmen response a lot to check out their surroundings. When they open their mouths, like that, it helps them take in air with pheromones that go to the Jacobson’s organ. This organ picks up on the chemical signals, sending nerve impulses to the brain that can affect behaviors like mating and aggression.

Behavioral influences

  • Reproductive: The organ is instrumental in detecting pheromones that trigger estrus cycles and encourage mating behaviors.
  • Territorial: It plays a role in scent marking and the recognition of territorial boundaries, critical for feline social structure.
  • Social: Jacobson’s organ helps in kitten-mother bonding and establishing group hierarchies by interpreting pheromones and other chemical cues.1
A jaguar with closed eyes and a wide-open mouth.
Bernard Dupont, CC BY-SA 2.0, via Wikimedia Commons

Anatomical overview of Jacobson’s organ

While we cannot see Jacobson’s organ from the outside, we can still see the incisive papilla. This is the primary entry point for chemical sgnals to reach Jacobson’s organ. Once entered through incisive ducts, the scent particles reach Jacobson’s organ which is located above the roof of the mouth in the nasopalatine canal.

A line drawing of the upper cat's mouth in cross-section. The Jacobson's organ is visible directly behind the teeth.
The vomeronasal organ (VNO) or Jacobson’s organ of the cat2

The organ comprises two tubular channels that run side by side, each lined with sensory epithelial cells. These cells detect and transduce the chemical signals into nerve impulses. These impulses are then relayed to the accessory olfactory bulb in the brain, which interprets the signals and can trigger instinctual behaviors related to social interaction, mating, and territoriality.

This process allows cats and other animals with this organ to respond to nuanced environmental cues that are undetectable to the human senses. This user on reddit detected a little round thingy that is actually the incisive papilla.

Maybe now you understand why animals curl back their upper lip and tilt their heads when using this organ. Speaking of them, there are many other creatures in the animal kingdom making use of it.

Which other mammals have Jacobson’s organ?

Jacobson’s organ is found in many other mammals. Ungulates like sheep, goats, buffalo, and bison use it to assess mating readiness and establish social hierarchies. Odd-toed ungulates, including rhinoceroses and tapirs, also exhibit Flehmen for mating and environmental communication. In contrast, canines like dogs have a less pronounced use for it, mainly for scent investigation, while in rodents, it’s crucial for social and reproductive signaling. Humans lack a functional Jacobson’s organ, relying instead on complex social and verbal communication, indicative of an evolutionary shift away from pheromone-based cues.

A red deer holding its head up and pulling its front lip upwards.
Böhringer Friedrich, CC BY-SA 2.5, via Wikimedia Commons

Future research directions

  • Genetic engineering: There’s potential for modifying pheromone detection capabilities to influence behavior profoundly.
  • Pheromone-based treatments: Exploring treatments for behavioral disorders using pheromones is a promising frontier in veterinary medicine.

If you’ve gotten curious about other feline anatomy features, you should check our article about cat anatomy for beginners! Otherwise leave a comment about what you think is the most interesting fact about Jacobson’s organ.

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