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11 Facts About the Thumb

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The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

When it comes to the fingers on your hand, the thumb definitely does its own thing. Thumbs only have two bones, so they're obviously shorter, and they play a very important role that no other finger can claim; thanks to their unique saddle-like joint shape, and a little muscle known as the abductor pollicis brevis, you can bend and stretch your thumbs opposite your fingers to grip things. This is why they're known as "opposable thumbs." To bring you these 11 facts about the thumb, Mental Floss spoke with three experts on this unique digit: Barbara Bergin, an orthopedic surgeon in Houston; Loren Fishman, medical director of Manhattan Physical Medicine and Rehabilitation, in NYC; and Ryan Katz, attending hand surgeon at the Curtis Hand Center, located at the Medstar Union Memorial Hospital in Baltimore.

1. OPPOSABLE THUMBS MAY HAVE FREED UP OUR ANCESTORS' MOUTHS FOR LANGUAGE.

The evolution of a thumb helped our ancestors evolve to be better at defense, allowing for throwing and clubbing activities. Moreover, Fishman says, it may have even contributed to our cognitive function. "Some say this is why we have language," he says, "because we can hold things in our hands and [therefore] use our mouths for something else—such as discussing the functions of the thumb."

2. THUMBS HAVE THEIR OWN PULSE.

You might have noticed that medical professionals take a pulse with the middle and index finger. The reason is because there's a big artery in the thumb, the princeps pollicis artery, and arteries pulse, making it difficult to feel a pulse in a neck if you're using your thumb.

3. THE THUMB SEPARATES US FROM OTHER ANIMALS. MOSTLY.

"The thumb is wonderful. It evolved in such a way that we can use it to do so many amazing things, and it's one of the things that separates us from other animals," Bergin says. A handful of other animals, mostly primates, have opposable thumbs, or toes, as the case may be. These include orangutans, chimpanzees, a phylum of frogs known as phyllomedusa, some lemurs, and giant pandas—although their thumb-like apparatus is really just an extra sesamoid bone that acts like a thumb.

4. TOES CAN BECOME THUMBS.

If you should lose a thumb, fear not, says Katz. "It can be rebuilt by surgeons using your big toe." This specialized surgery uses microvascular surgery techniques to transfer your big toe to your hand, where it will function almost exactly as your thumb did. "The toe is then brought to life by sewing together small arteries and veins under a microscope," Katz says, a complicated surgery that has become vastly more sophisticated over the years. The second toe can be used too, as you can see in this medical journal, but we warn you: It's not for the faint of heart.

5. … BUT IS A THUMB WORTH LOSING A TOE OVER?

It may not seem like a big deal to lose one thumb—after all, you've got another one. But Katz cites the American Medical Association's "Guides to the Evaluation of Permanent Impairment" [PDF], which states your thumb is so important that a complete amputation "will result in a 40 percent impairment to the whole hand." In fact, they claim that it would take "a complete amputation of the middle, ring, and small fingers to equal the impairment of an amputated thumb."

6. IT'S BETTER THAN HAVING YOUR HAND SEWN TO YOUR FOOT.

Katz also points out that "there used to be a common surgical procedure for thumb reconstruction, where the patient's hand was sewn to their foot for a period of time." This procedure was called the Nicoladani procedure, after the German surgical innovator Carol Nicoladoni. "It was a precursor to transplant surgery and plastic or reconstructive surgery as we know it today," he says.

7. YOUR THUMB MAKES AN ASTONISHINGLY WIDE VARIETY OF MOTIONS.

Other than pinching and grasping, Katz points out that the thumb "translates, rotates, and flexes all at once." This coordinated set of motions provides strength and dexterity. "Thus it's the thumb that allows us to easily pen an essay, turn a nut, pick up a coin, or button a shirt."

8. THAT DEXTERITY ALSO MAKES IT FRAGILE.

The thumb may appear to only have two knuckles, but it actually has a third, right above the wrist. This is called the first carpometacarpal joint. If that starts to hurt, or gets big enough to look like a bump or a mass, you may have carpometacarpal joint disorder (CMC), a common condition that is partly genetic and partly from repetitive use, according to Bergin. "You can get arthritis in the other joints, too, but this one is the most debilitating," she says. "First it becomes painful, and then you lose the ability to use it." Surgery can help with the pain, but it won't restore full mobility.

9. PAIN IN YOUR THUMB MAY REQUIRE LIFESTYLE CHANGES.

Bergin suggests small lifestyle changes so you don't need to grip anything too hard can make a huge difference, such as buying milk jugs with handles or using an electric toothbrush. "There are a lot of things we can do [to help] on a daily basis that shouldn't affect our quality of life," she suggests.

10. SWIPING RIGHT MIGHT BE DANGEROUS.

While we generally associate thumb arthritis with older people, Bergin says she now sees it in people in their forties and even thirties. Other studies have suggested that frequent phone use can be damaging. "There must be a genetic component to premature wearing of the thumb," she says. If it runs in your family, it's a good idea to be proactive and try to avoid repetitive gripping activities.

11. WHAT IT MEANS IF YOUR THUMB IS NUMB.

If instead of pain you're experiencing numbness of the thumb that extends to your index and middle fingers, you may be showing early symptoms of carpal tunnel syndrome. Fortunately, this isn't an emergency. "The condition takes a long time to become a big problem" Bergin says. People can sometimes help the condition by wearing wrist braces and getting physical therapy. If you just can't take it, "you can get surgery at any point if you failed to improve with bracing," she says. The surgery can reduce mobility, but it should take away the numbness and pain.

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12 Fantastic Facts About the Immune System
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The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

If it weren't for our immune system, none of us would live very long. Not only does the immune system protect us from external pathogens like viruses, bacteria, and parasites, it also battles cells that have mutated due to illnesses, like cancer, within the body.

Here are 12 fighting facts about the immune system.

1. THE IMMUNE SYSTEM SAVES LIVES.

The immune system is a complex network of tissues and organs that spreads throughout the entire body. In a nutshell, it works like this: A series of "sensors" within the system detects an intruding pathogen, like bacteria or a virus. Then the sensors signal other parts of the system to kill the pathogen and eliminate the infection.

"The immune system is being bombarded by all sorts of microbes all the time," Russell Vance, professor of immunology at University of California, Berkeley and an investigator for the Howard Hughes Medical Institute, tells Mental Floss. "Yet, even though we're not aware of it, it's saving our lives every day, and doing a remarkably good job of it."

2. BEFORE SCIENTISTS UNDERSTOOD THE IMMUNE SYSTEM, ILLNESS WAS CHALKED UP TO UNBALANCED HUMORS.

Long before physicians realized how invisible pathogens interacted with the body's system for fighting them off, doctors diagnosed all ills of the body and the mind according to the balance of "four humors": melancholic, phlegmatic, choleric, or sanguine. These criteria, devised by the Greek philosopher Hippocrates, were divided between the four elements, which were linked to bodily fluids (a.k.a. humors): earth (black bile), air (blood), water (phlegm) and fire (yellow bile), which also carried properties of cold, hot, moist, or dry. Through a combination of guesswork and observation, physicians would diagnose patients' humors and prescribe treatment that most likely did little to support the immune system's ability to resist infection.

3. TWO MEN WHO UNRAVELED THE IMMUNE SYSTEM'S FUNCTIONS WERE BITTER RIVALS.

Two scientists who discovered key functions of the immune system, Louis Pasteur and Robert Koch, should have been able to see their work as complementary, but they wound up rivals. Pasteur, a French microbiologist, was famous for his experiments demonstrating the mechanism of vaccines using weakened versions of the microbes. Koch, a German physician, established four essential conditions under which pathogenic bacteria can infect hosts, and used them to identify the Mycobacterium tuberculosis bacterium that causes tuberculosis. Though both helped establish the germ theory of disease—one of the foundations of modern medicine today—Pasteur and Koch's feud may have been aggravated by nationalism, a language barrier, criticisms of each other's work, and possibly a hint of jealousy.

4. SPECIALIZED BLOOD CELLS ARE YOUR IMMUNE SYSTEM'S GREATEST WEAPON.

The most powerful weapons in your immune system's arsenal are white blood cells, divided into two main types: lymphocytes, which create antigens for specific pathogens and kill them or escort them out of the body; and phagocytes, which ingest harmful bacteria. White blood cells not only attack foreign pathogens, but recognize these interlopers the next time they meet them and respond more quickly. Many of these immune cells are produced in your bone marrow but also in the spleen, lymph nodes, and thymus, and are stored in some of these tissues and other areas of the body. In the lymph nodes, which are located throughout your body but most noticeably in your armpits, throat, and groin, lymphatic fluid containing white blood cells flows through vein-like tubules to escort foreign invaders out.

5. THE SPLEEN HELPS YOUR IMMUNE SYSTEM WORK.

Though you can live without the spleen, an organ that lies between stomach and diaphragm, it's better to hang onto it for your immune function. According to Adriana Medina, a doctor who specializes in hematology and oncology at the Alvin and Lois Lapidus Cancer Institute at Sinai Hospital in Baltimore, your spleen is "one big lymph node" that makes new white blood cells, and cleans out old blood cells from the body.

It's also a place where immune cells congregate. "Because the immune cells are spread out through the body," Vance says, "eventually they need to communicate with each other." They do so in both the spleen and lymph nodes.

6. YOU HAVE IMMUNE CELLS IN ALL OF YOUR TISSUES.

While immune cells may congregate more in lymph nodes than elsewhere, "every tissue in your body has immune cells stationed in it or circulating through it, constantly roving for signs of attack," Vance explains. These cells also circulate through the blood. The reason for their widespread presence is that there are thousands of different pathogens that might infect us, from bacteria to viruses to parasites. "To eliminate each of those different kinds of threats requires specialized detectors," he says.

7. HOW FRIENDLY YOU'RE FEELING COULD BE LINKED TO YOUR IMMUNE SYSTEM.

From an evolutionary perspective, humans' high sociability may have less to do with our bigger brains, and more to do with our immune system's exposure to a greater number of bacteria and other pathogens.

Researchers at the University of Virginia School of Medicine have theorized that interferon gamma (IG), the immune cytokine that helps the immune system fight invaders, was linked to social behavior, which is one of the ways we become exposed to pathogens.

In mice, they found IG acted as a kind of brake to the brain's prefrontal cortex, essentially stopping aberrant hyperactivity that can cause negative changes in social behavior. When they blocked the IG molecule, the mice's prefrontal cortexes became hyperactive, resulting in less sociability. When they restored the function, the mice's brains returned to normal, as did their social behavior.

8. YOUR IMMUNE SYSTEM MIGHT RECRUIT UNLIKELY ORGANS—LIKE THE APPENDIX—INTO ITS SERVICE.

The appendix gets a bad rap as a vestigial organ that does nothing but occasionally go septic and create a need for immediate surgery. But the appendix may help keep your gut in good shape. According to Gabrielle Belz, professor of molecular immunology at the Walter and Eliza Hall Institute of Medical Research in Melbourne, Australia, research by Duke University's Randal Bollinger and Bill Parker suggests the appendix houses symbiotic bacteria that are important for overall gut health—especially after infections wipe out the gut's good microbes. Special immune cells known as innate lymphoid cells (ILCs) in the appendix may help to repopulate the gut with healthy bacteria and put the gut back on track to recovery.

9. GUT BACTERIA HAS BEEN SHOWN TO BOOST IMMUNE SYSTEMS IN MICE.

Researchers at the University of Chicago noticed that one group of mice in their lab had a stronger response to a cancer treatment than other mice. They eventually traced the reason to a strain of bacteria—Bifidobacterium—in the mice's guts that boosted the animals' immune system to such a degree they could compare it to anti-cancer drugs called checkpoint inhibitors, which keep the immune system from overreacting.

To test their theory, they transferred fecal matter from the robust mice to the stomachs of less immune-strengthened mice, with positive results: The treated mice mounted stronger immune responses and tumor growth slowed. When they compared the bacterial transfer effects with the effects of a checkpoint inhibitor drug, they found that the bacteria treatment was just as effective. The researchers believe that, with further study, the same effect could be seen in human cancer patients.

10. SCIENTISTS ARE TRYING TO HARNESS THE IMMUNE SYSTEM'S "PAC-MAN" CELLS TO TREAT CANCER.

Aggressive pediatric tumors are difficult to treat due to the toxicity of chemotherapy, but some researchers are hoping to develop effective treatments without the harmful side effects. Stanford researchers designed a study around a recently discovered molecule known as CD47, a protein expressed on the surface of all cells, and how it interacts with macrophages, white blood cells that kill abnormal cells. "Think of the macrophages as the Pac-Man of the immune system," Samuel Cheshier, lead study author and assistant professor of neurosurgery at Stanford Medicine, tells Mental Floss.

CD47 sends the immune system's macrophages a "don't eat me" signal. Cancer cells fool the immune system into not destroying them by secreting high amounts of CD47. When Cheshier and his team blocked the CD47 signals on cancer cells, the macrophages could identify the cancer cells and eat them, without toxic side effects to healthy cells. The treatment successfully shrank all five of the common pediatric tumors, without the nasty side effects of chemotherapy.

11. A NEW THERAPY FOR TYPE 1 DIABETES TRICKS THE IMMUNE SYSTEM.

In those with type 1 diabetes, the body attacks its own pancreatic cells, interrupting its normal ability to produce insulin in response to glucose. In a 2016 paper, researchers at MIT, in collaboration with Boston's Children's Hospital, successfully designed a new material that allows them to encapsulate and transplant healthy pancreatic "islet" cells into diabetic mice without triggering an immune response. Made from seaweed, the substance is benign enough that the body doesn't react to it, and porous enough to allow the islet cells to be placed in the abdomen of mice, where they restore the pancreatic function. Senior author Daniel Anderson, an associate professor at MIT, said in a statement that this approach "has the potential to provide [human] diabetics with a new pancreas that is protected from the immune system, which would allow them to control their blood sugar without taking drugs. That's the dream."

12. IMMUNOTHERAPY IS ON THE CUTTING EDGE OF IMMUNE SYSTEM RESEARCH.

Over the last few years, research in the field of immunology has focused on developing cancer treatments using immunotherapy. This method engineers the patient's own normal cells to attack the cancer cells. Vance says the technique could be used for many more conditions. "I feel like that could be just the tip of the iceberg," he says. "If we can understand better what the cancer and immunotherapy is showing, maybe we can go in there and manipulate the immune responses and get good outcomes for other diseases, too."

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Why Is Your First Instinct After Hurting Your Finger to Put It in Your Mouth?
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If you close your fingers in a car door or slam your funny bone into a wall, you might find your first reaction is to suck on your fingers or rub your elbow. Not only is this an instinctive self-soothing behavior, it's a pretty effective technique for temporarily calming pain signals to the brain.

But how and why does it work? To understand, you need to know about the dominant theory of how pain is communicated in the body.

In the 17th century, French scientist and philosopher René Descartes proposed that there were specific pain receptors in the body that "rang a bell in the brain" when a stimulus interacted with the body, Lorne Mendell, a professor of neurobiology and behavior at Stony Brook University in New York, tells Mental Floss. However, no study has effectively been able to identify receptors anywhere in the body that only respond to painful stimuli.

"You can activate certain nerve fibers that can lead to pain, but under other circumstances, they don't," Mendell says. In other words, the same nerve fibers that carry pain signals also carry other sensations.

In 1965, two researchers at MIT, Patrick Wall and Ronald Melzack, proposed what they called the gate control theory of pain, which, for the most part, holds up to this day. Mendell, whose research focuses on the neurobiology of pain and who worked with both men on their pain studies, explains that their research showed that feeling pain is more about a balance of stimuli on the different types of nerve fibers.

"The idea was that certain fibers that increased the input were ones that opened the gate, and the ones that reduced the input closed the gate," Mendell says. "So you have this idea of a gate control sitting across the entrance of the spinal cord, and that could either be open and produce pain, or the gate could be shut and reduce pain."

The gate control theory was fleshed out in 1996 when neurophysiologist Edward Perl discovered that cells contain nociceptors, which are neurons that signal the presence of tissue-damaging stimuli or the existence of tissue damage.

Of the two main types of nerve fibers—large and small—the large fibers carry non-nociceptive information (no pain), while small fibers transmit nociceptive information (pain).

Mendell explains that in studies where electric stimulation is applied to nerves, as the current is raised, the first fibers to be stimulated are the largest ones. As the intensity of the stimulus increases, smaller and smaller fibers get recruited in. "When you do this in a patient at low intensity, the patient will recognize the stimulus, but it will not be painful," he says. "But when you increase the intensity of the stimulus, eventually you reach threshold where suddenly the patient will say, 'This is painful.'"

Thus, "the idea was that shutting the gate was something that the large fibers produced, and opening the gate was something that the small fibers produced."

Now back to your pain. When you suck on a jammed finger or rub a banged shin, you're stimulating the large fibers with "counter irritation," Mendell says. The effect is "a decrease in the message, or the magnitude of the barrage of signals being driven across the incoming fiber activation. You basically shut the gate. That is what reduces pain."

This concept has created "a big industry" around treating pain with mild electrical stimulation, Mendell says, with the goal of stimulating those large fibers in the hopes they will shut the gate on the pain signals from the small fibers.

While counter irritation may not help dull the pain of serious injury, it may come in handy the next time you experience a bad bruise or a stubbed toe.

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