Sixth Sense: What Is the Jacobson's Organ?

Posted by Stacey Venzel
Jacobson's organ

Some animals have an extra sensory receptor called the Jacobson's Organ for detecting special smells.

If you ever thought snakes, lizards, horses, cats, and dogs had superpowers, you're technically correct.

Initially discovered by Frederick Ruysch in the 1700s and then brought to the spotlight again by Ludwig Jacobson in the 1800s, the Jacobson's organ, located on the roof of the mouth, is an extension of the olfactory system, allowing certain animals to detect scents typically outside the nasal range.

VNO
Henry Gray/Wikipedia

Also known as the vomeronasal organ (VNO), the organ is stimulated by moisture-borne scent particles as they pass through the nasal cavity and over the olfactory bulbs. While typical odor is picked up through the air, the Jacobson's organ detects chemical smells essentially through humidity.

Animals known to have a great sense of smell likely have this adaptation. Many, but not all, types of reptiles, amphibians, and mammals have vomeronasal sensory neurons. Humans also have a nasal fold that resembles the Jacobson's organ but it is thought to be vestigial--meaning, like the appendix, the human vomeronasal organ no longer serves a functional purpose.

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Snakes, known for flicking their tongues to gather scent, actually touch their tongue inside their mouth to the vomeronasal receptor in order to process the odor and comprehend different chemical messages left by other animals.

Many animals, like goats and horses, even expose their VNO, or vomeronasal openings, during what is called the flehmen response. During this process, the animal curls back its upper lip so that the teeth show. Then, they inhale deeply often with the nostrils closed so that the Jacobson's organ picks up on most of the scent through the sensory cells. Animals often remain in the flehmen reaction for a few seconds in order for the vomeronasal system to read the chemical stimuli.

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The flehmen response is often observed near excrement, such as urine or feces, to pick up on pheromone receptors, which are a form of chemical communication between animals. Male dogs, for example, use scent marking by urinating to establish their territory through chemical signals, whereas cats will rub their scent glands against objects to make their mark.

Can you take at guess at some other animals that have a Jacobson's organ?

What animals have you seen do the flehmen response? Tell us in the comments below!

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Sixth Sense: What Is the Jacobson's Organ?