Sixth Sense: The Vomeronasal Organ Essay

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Sixth Sense: The Vomeronasal Organ

"We are all more influenced by smell than we know." (Hercule Poirot)
....Murder in Retrospect, Agatha Christie

Biologists have long realized that the noses of most vertebrates actually contain two sensory channels. The first is the familiar olfactory system, which humans possess. The second channel is the vomeronasal complex, a system that has its own separate organs, nerves, and connecting structures in the brain. The function of the vomeronasal system is the detection of pheromones, chemical messengers that carry information between individuals of the same species. It was widely believed (as I found in some of the older texts I examined) that humans had long ago discarded this sensory system
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In a recent experiment, human VNO was reported to respond positively (by emitting electrical signals) to puffs of air laden with substances claimed to be human pheromones (2). If the experiment is valid, it presents strong evidence supporting the hypothesis that the human VNO is functioning, not vestigial. In some respects, however, the proof is lacking. The human VNO lacks the characteristic capsule and large blood vessels of other mammals' VNOs (2). The sensory epithelium, as mentioned earlier, is not well developed. In addition, connections between the presumed VNO receptor neurons and the brain have not yet been confirmed in humans. In other mammals, nerve impulses from the sensory cells of the vomeronasal organ enter brain structures known as the accessory olfactory bulbs and also project to brain structures that regulate sexual behavior and the secretion of gonadotropin, a pituitary hormone regulating the function of the testes (4). The accessory olfactory bulb, the normal termination of vomeronasal receptor-neuron axons (i.e. the doorway to the brain for these signals), cannot be distinguished clearly in the human brain (2). But, the structural inconsistencies (shortcomings?) of the human VNO system do not prove that it is inactive. They merely indicate that it different, and perhaps less fundamental, than in our fellow vertebrates, a notion that is readily apparent from more cursory observations. Recent

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