英语听力在线学习:英语听力文章学习：狗狗嗅觉灵敏的原因

Watch a dog greeting the world with its nose, or following invisible trails of scent, and you might wonder what you’re missing. In one study, dogs were able to smell a particular test scent a thousand times better than humans! What makes dogs such stupendous sniffers?

Smell Receptors

Like humans, dogs have special smell receptor cells lining their noses. But dogs have about 20 times more of these cells than we do–and the differences don’t stop there!

From the receptor cells, information about smell travels along nerves to the olfactory bulbs, the parts of the brain where information about smell is processed. Relative to the size of its brain, a dog’s olfactory bulbs are much bigger than most other animals. If the animal kingdom held a sniffing Olympics, dogs and rats would probably battle for the gold, leaving the rest of us in the dust.

Tongue Transportation

Another advantage dogs have is that the schnoz isn’t the only tool they use for smelling. When a dog licks your hand, or something less savory found in the street, its tongue transports molecules from that surface into its mouth. Just above the roof of the dog’s mouth is the vomeronasal organ, which gathers information on smell from the molecules the tongue delivers. Humans have vomeronasal organs, too, but compared to dogs, ours are very rudimentary.

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