The Body: A Guide for Occupants

by Bill Bryson

The vestibular system does everything that a gyroscope does on an airplane, but in an extremely miniaturized form.

When loss of balance is prolonged or severe, the brain doesn’t know quite what to make of it and interprets it as poisoning. That is why loss of balance so generally results in nausea.

It is known as the Valsalva effect, and it arises because the air pressure inside your head fails to keep up with the changing air pressure outside it. Making your ears pop by blowing out while keeping your mouth and nose closed is known as the Valsalva maneuver.

As your mother doubtless told you, you shouldn’t blow too hard. People have ruptured eardrums from doing so.

Smell is, in fact, a lot more important to happiness and fulfillment than most people appreciate.

If the right kind of molecule activates the right kind of receptor, it sends a signal to the brain, which interprets it as a smell. How exactly this happens is where the controversy lies. Many authorities believe the odor molecules fit into the receptors like a key into a lock.

If you combine the fruity odor of ethyl isobutyrate with the caramel-like allure of ethyl maltol and the violet scent of allyl alpha-ionone, you get pineapple, which smells wholly unlike its three principal inputs.

The smell of burned almonds can be produced by seventy-five different chemical combinations that have nothing in common beyond how the human nose perceives them.

An interesting and important curiosity of our sense of smell is that it is the only one of the five basic senses not mediated by the hypothalamus.

When we smell something, the information, for reasons unknown, goes straight to the olfactory cortex, which is nestled close to the hippocampus, where memories are shaped, and it is thought by some neuroscientists that that may explain why certain odors are so powerfully evocative of memories for us.

“I think the single most extraordinary aspect of olfaction is that we all smell...

“It’s a hormone called androsterone,” Beauchamp explained. “About a third of people, like you, can’t smell it. One-third smell something like urine, and one-third smell sandalwood.” His smile broadened. “If you have three people who cannot even agree on whether something is pleasant, revolting, or simply odorless, you begin to see how complicated the science of smell is.”

Smell, in short, is much more important to us than we appreciate.

One of the early symptoms of Alzheimer’s is smell loss.

“People who lose their sense of smell are usually astounded at how much pleasure it takes out of their lives,”

To lengthen thy life, lessen thy meals. —benjamin franklin

Indeed, it can reasonably be said that we are built to choke, which is clearly an odd attribute to go through life with—with

When you swallow, food doesn’t just drop into your stomach by means of gravity, but is pushed down by muscular contractions. That’s why you can eat and drink while upside down if you choose to.

The problem is that, we send our air and food down the same tunnel.

But even using the most cautious estimates, choking is the fourth most common cause of accidental death in America today.

“abdominal thrusts.”

Just recently it was discovered that saliva also contains a powerful painkiller called opiorphin.

Unfortunately for us, bacteria in our mouths like that sweetness, too; they devour the liberated sugars and excrete acids, which drill through our teeth and give us cavities.

We are in the rather strange position that we not only fail to kill the bacteria that give us a lot of trouble but actively nurture them.

We produce very little saliva while we sleep, which is why microbes can proliferate then and give you a foul mouth to wake to.

microbially speaking, your tongue, teeth, and gums are like separate continents, each with its own colonies of microorganisms.

“Bacterial Transfer Associated with Blowing Out Candles on a Birthday Cake,”

enamel.

is the hardest substance in the human body, but forms just a thin layer and can’t be replaced if it is damaged.

Still, when you consider how well you can demolish, say, an ice cube (try doing that with your fists and see how far you get) and how little space the five muscles of the jaw occupy, you can appreciate that human chomping is pretty capable.

The tongue is a muscle, but quite unlike any other.

They are among the most regenerative of all cells in the body and are replaced every ten days.

Altogether we have about ten thousand taste buds, mostly distributed around the tongue, except in the very middle, where there are none at all.

Additional taste buds are found in the roof of the mouth and lower down the throat, which is said to be why some medicines taste bitter as they go down.

As well as the mouth, the body has taste receptors in the gut and throat (to help identify sp...

Taste receptors have also been found in the heart, the lungs, and even the testicles.

It is generally supposed that taste receptors evolved for two deeply practical purposes: to help us find energy-rich foods (like sweet, ripe fruits) and to avoid dangerous ones.

Because they exist side by side on the tongue, we sometimes mix them up. When you describe a chili as hot, you are being more literal than you might suppose. Your brain interprets it as being actually burned.

In the same way, menthol is perceived as being cool even in the heated smoke of a cigarette.

The record holder at the time of writing is the Carolina Reaper at 2.2 million Scovilles.

Incidentally, we have pain detectors not only in the mouth but also in the eyes, anus, and vagina, which is why spicy foods can cause discomfort there.

Smell is said to account for at least 70 percent of flavor, and maybe even as much as 90 percent.

We appreciate this intuitively without often thinking about it. If someone hands you a pot of yogurt and says, “Is this strawberry?” your response will normally be to sniff it, not taste it. That is because strawberry is actually a smell, perceived nasally, not a taste in the mouth.

When you eat, most of the aroma reaches you not through your nostrils but by the back stair...

An easy way to experience the limitations of your taste buds is to close your eyes, pinch shut your nostrils, and eat a flavored jelly bean collected blindly from a bowl. You will instantly apprehend its sweetness, but you almost certainly won’t be able to identify its flavor. But open your eyes and ...

In exactly the same way, if an orange-flavored drink is colored red, you cannot help but taste it as cherry.

The fact is that odors and flavors are created entirely inside our heads.

Speech and its evolution “are perhaps more extensively debated than any other topic in human evolution,”

That’s quite a tall order, to put it mildly. It isn’t just a big brain that allows us to speak but an exquisite arrangement of anatomy.

When air is forced through them, the vocal folds snap and flutter (like flags in a stiff breeze, it has been said), producing a variety of sounds, which are refined by tongue, teeth, and lips working together into the wondrous, resonant, informative exhalations known as speech.