banner link to Perelman School of Medicine Biochemistry and Biophysics
biochemistry and biophysics

TRIVIA ARCHIVE: 2012 - 2013 - 2014


What is the only remaining wonder of the ancient world that is still standing?

The Great Pyramid at Giza

Unlike the list of natural wonders, the seven wonders of the ancient world are man-made structures that serve as a testament to the ingenuity, imagination, and hard work of which human beings are capable. At its inception, the sites were not “wonders” but “theamata” or “things to be seen”. The collection was more like a Greek travel guide’s idea of places not to be missed. The definitive set of wonders is believed to have been finalized during the Middle Ages.

Of the seven, just one remains to this day: the Great Pyramid at Giza. The last wonder of the ancient world in existence was also the first one built. The pyramid was built as a tomb for Egyptian Pharaoh Khufu around 2560 B.C. It took 20 years to construct. When finished, it stood 480 feet high and remained the tallest building in the world for the next four thousand years.

The Great Pyramid at Giza and the others standing with it have stood for four and a half thousand years and counting.

What wonder of the ancient world stood the least amount of time?

The Colossus at Rhodes

The Colossus at Rhodes was an enormous looming 100-foot bronze statue that was built on the island of Rhodes around 280 B.C. It depicts the island’s patron god, Greek sun god Helios.

No drawings of the statue survive but it has been described as an upright figure with face mostly likely modeled after Alexander the Great, holding a torch not unlike the Statue of Liberty.

It was long believed that the statue straddled the harbor entrance with ships passing in and out between its legs. Modern archeologists say this would have not been possible with the bronze casting techniques available at the time.

The statue was destroyed in 226 B.C., after a mere 54 years.

How was the Colossus of Rhodes destroyed?

An earthquake

The Colossus was built between 292 and 280 B.C. and was placed at the entrance to the harbor of the Greek Island of Rhodes. The statue stood 98 feet tall and was erected to honor their patron god, Helios.

Rhodes experienced an earthquake in 224 B.C. that broke the Colossus at the knees and toppled the top portion to the ground. People believed Helios was angered by the statue and did not rebuild it.

Even broken, the pieces were impressive. For the next 900 years, the ruins lay on the ground attracting visitors from all over the world. Few people could wrap their arms around the fallen thumb and each of its fingers was larger than most statues.

In 654 A.D., Arabs conquered Rhodes, transported the remains to Syria, and most likely melted them down and sold them for scrap metal.

What wonder of the ancient world may never have existed at all?

The Hanging Gardens of Babylon

The Hanging Gardens were said to have been built ~600 B.C. in the Babylon province of Iraq, south of Bagdad. There is no existing Babylonian text that mentions the gardens and no definitive archeological evidence has been found for them.

According to the legend, King Nebuchadnezzar built the gardens for his wife because she missed the green hills and valleys of her homeland. He built a man-made mountain with lush vegetation and cascading waterfalls. Plants high above the ground on multi-stone terraces gave the appearance of hanging. Stone pillars supported high walkways.

The Hanging Gardens would certainly have been a marvel of engineering and construction, but did they exist?

A researcher at Oxford University says yes! Dr. Stephanie Dalley believes that we had the location wrong. The Hanging Gardens may never have been in Babylon but instead 300 miles to the north outside the city of Nineveh. Ancient texts describe the life of the great Assyrian ruler, Sennacherib, with detailed descriptions of his palace and his garden with trees hanging in air.

The location proposed by Dr. Dalley as the correct site of the Hanging Gardens is near Mosul in Iraq. Because it is at this time the site of continuing violence, it is unsafe for archeological work. The destruction during the current wars and the pillaging over the years may erase any trace of an ancient hanging garden.

What ancient wonder was built in honor of the Olympic games?

The Statue of Zeus

A massive gold statue honoring the king of all Greek gods, Zeus, was built around 432 BC in Olympia, the site of the first Olympic games. The figure sat on a jewel-encrusted throne inside a temple overlooking the city.

In 391 AD, the Olympics were banned as a pagan practice and the temple was closed after Christianity had become the official religion of the Roman Empire.

The statue was eventually destroyed but historians debate whether it perished with the temple or was moved to Constantinople and burned in a fire.

The complete list of ancient wonders is: The Great Pyramid at Giza, Statue of Zeus at Olympia, Colossus of Rhodes, Lighthouse at Alexandra, Mausoleum at Halicarnassus, Temple of Artemis at Ephesus, and the Hanging Gardens at Babylon

What is an organism’s complete set of DNA called?


A genome is an organism’s complete set of DNA including all its genes. Each genome contains all the information needed to build and maintain that organism.

In humans, a copy of the entire genome is contained in all cells that have a nucleus.

The typical human body has an estimated 25,000 genes and has an enormous amount of DNA that does not code for RNA or protein. Managing so much DNA requires that the genome be elaborately organized and compact.

DNA wraps around proteins called histones, and together they make chromatin.

Why doesn’t chromatin fall apart?

Electrostatic interactions

The attraction between the negatively-charged DNA and the positively-charged histones binds them tightly together.

Every cell in a human body has the exact same DNA and yet they make different organs. The protein coding part of the genome, called genes, do not make proteins all the time in all of the cells. Sections of DNA are marked, signaling which genes to ignore and which to use.

Chromatin can open and close. If a region is open, that area is turned “on” and protein can be made. If a region is closed, that area is being prevented from being turned on.

What do we call the collection of chemical compounds that modify, or mark, the genome that tells it what to do, where to do it, and when to do it?

The epigenome

Our genome is something we are born with and cannot modify. Our epigenome contains "instructions" on how to use the genome. “Epi” comes from the Greek word “above”.

These are small chemical modifications on histones or DNA that give instructions on how to "read" and "use" our genes. Like traffic lights.

A gene that is turned "on" is producing protein so we call it an “active gene". One that is turned "off" is not producing protein and is called a "silent gene".

Some genes are always active (housekeeping genes), some genes are active only at certain times in the development of an organism (developmental genes), some genes are active only in certain tissues like the heart or eye (tissue-specific genes), while some genes are being turned on and off many times.

The pattern of activity of certain genes (the epigenome) is inherited from your parents (just like the genome), but it is also very susceptible to influences from the environment.

Who proposed the Law of Inheritance of Acquired Characteristics?

Jean-Baptiste Lamarck

Throughout the years, the French naturalist Lamarck has gone in and out of favor. Lamarck understood that all species are descended from a common ancestor and he was the first person to propose a cohesive evolutionary theory of how a species mutated over time, a theory that paralleled Charles Darwin’s.

He believed that an organism could pass on characteristics that it acquired during its lifetime to its offspring.
During Lamarck’s life (1744-1829), his ideas were not respected. He died in obscurity and poverty.

In the mid-19th century, his Law of Inheritance of Acquired Characteristics was rediscovered but fell out of favor in the early 20th century when Mendel’s work with genes was finally understood.

Interest in Lamarck’s ideas has resurfaced as studies in the epigenetic field have highlighted the possible inheritance of behavioral traits acquired by the previous generation.

What is that part of the cell cycle when the nucleus divides?


The continuity of life is based on cell division. After an organism is completely grown, cell division continues to function in renewal and repair.

In preparation for cell division, DNA duplicates itself. After duplication, the chromatin fibers coil, fold, and are packed into chromosomes. Each chromosome has two sister chromatids.

During mitosis, the cytoskeleton disappears and the nuclear envelope breaks down. Chromosomes move to the equator and line up. Proteins holding the chromosomes together break down and each chromosome is pulled to opposite ends of the cell.

The chromosomes disassemble and the nuclear envelope reforms. The division of the cytoplasm usually follows immediately after mitosis, and cell division is complete.

In its condensed form, a chromosome has a narrow “waist” where the sister chromatids are closely attached.  What is this area called?


The centromere is a constricted area to which specialized molecules called spindle fibers attach and help pull daughter cells apart during cell division.

Investigators have known for many years that cell division is controlled by epigenetic processes rather than encoded in the DNA itself. Epigenetics mark the place where spindle fibers attach to the chromosome independent of the underlying DNA sequence. Researchers have suspected the crucial epigenetic marker protein is the CENP-A molecule, which defines part of the centromere.

Ben Black and his lab have described the structure of CENP-A. The Black lab gave the first high-resolution view of the CENP-A molecule and described the structural features that confer the CENP-A the ability to mark centromere location.

The understanding of CENP-A and the epigenetics associated with cell division help advance the science of human inheritance.

How many chromosomes are in a single cell in the human body?


Each somatic cell in the human body has 22 pairs of chromosomes plus a pair of so-called sex chromosomes: two Xs for a female and an X and a Y for a male.

When chromosomes condense, they are visible under a light microscope. They are easily distinguished from one another because they differ in size, centromere location, and patterns produced when stained.

What is the name given to the mutation of chromosome 22 when it has swapped parts with chromosome 9?

Philadelphia chromosome

The relationship between chromosome alterations and cancer had been debated for many years until 1960. That year, the first direct link between chromosomal abnormalities to any malignancy came with the discovery of the Philadelphia chromosome.

Pieces of chromosome 9 were shown to have transferred to chromosome 22 and vice versa. 9 becomes exceptionally long and 22 is truncated. 

Peter Nowell in the School of Medicine here at Penn, along with his collaborator David Hungerford at the Fox Chase Cancer Center, established that certain forms of leukemia had cells with an abnormally small chromosome. This mutation of chromosome 22 was named after the city in which both researchers worked.

This discovery of the Philadelphia chromosome established that cancers can indeed be caused by genetic mutation.

Discoveries may be named after the cities in which they are identified. So can disease outbreaks. How did the Ebola virus disease get its name?

From the Ebola River

The first appearance of Ebola virus disease in humans occurred in 1976 in two simultaneous outbreaks in Africa. One happened in southern Sudan and the other in northern Zaire (now the Democratic Republic of Congo).

The outbreak in Zaire occurred in a village called Yambuku. When doctors and scientists realized this virus was unlike any they had seen before, it needed a name. They ruled out the name Yambuku so as not to stigmatize the village. They chose instead a landmark close by, the Ebola River.

Ebola is one of the deadliest viruses known to medical science with no specific cure and mortality rates of up to 90%.

The virus is transmitted to people from wild animals and spreads through human-to-human transmission.

The Ebola virus lives in:

  1. a) air
  2. b) bodily fluids
  3. c) water
  4. d) all of the above

b) bodily fluids

Ebola is a virus and a virus needs a host. Viruses are ribonucleic acid wrapped in a protein shell. They find a host cell, inject their genes into it, and hijack its replication machinery to produce more viruses. The Ebola virus is filament-like in structure, with large surface area giving the potential to  attack a number of cells.

Ebola cannot survive for long in air or water. Bodily fluids, on the other hand, make perfect hosts for viruses.

To catch Ebola, one would need to have direct physical contact with an infected person or animal, their body fluids, or with something they have touched.

It has been said that Ebola is highly infectious but not very contagious.

What type of animal is thought to be responsible for infecting humans in Africa?

The bat

It is thought that the fruit bats of the Pteropodidae family are the natural Ebola virus host, but the recent epidemic may have originated from an insectivorous bat. The clearcutting of forests in Africa have forced bats and other wildlife from their habitat and closer to people. The first outbreaks occurred in remote villages near tropical rainforests. Bats, particularly fruit bats, are often hunted and eaten.

Ebola is introduced to the human population through close contact with blood, secretions, organs, or other bodily fluids of infected animals.

It is believed that the current outbreak started when a child, not yet two years old, came in contact with an infected insectiverous bat. He then passed it on to his family. Eventually it spread throughout the village and then the region.

Monkeys and apes are also known to harbor the Ebola virus.

True or False: Once the host is dead, the virus is dead too.


The Ebola virus cannot live long in air or water for but it can survive in bodily fluids, blood especially, for days and even weeks if the conditions are right. People are infectious as long as their blood contains the virus – even after death. Virus particles can last for days or weeks in a drop of blood. Inside the body of a deceased person, the virus can probably remain alive for several months.

Funeral rituals in Africa often have mourners in direct contact with the body of the deceased person that spreads the disease even further.

Major steps to stop the spread of the disease are to avoid infectious bodily fluids and to bury the dead quickly.

Once infected with the Ebola virus, how long does it take before the symptoms start to show?

2 – 21 days

The incubation time – the interval from infection to the onset of symptoms – for Ebola virus disease (EVD) is two to twenty-one days. First symptoms include sudden onset of fever, feeling weak, muscle pain, headache, and sore throat. As the disease progresses, the patient will experience vomiting, rash, diarrhea, and may have internal and external bleeding. The disease is not contagious until symptoms start to show.

Diagnosing Ebola is difficult because the early symptoms are common to many illnesses. Laboratory testing is the only way of definitively diagnosing Ebola. There is no specific treatment approved for Ebola. At the moment, Ebola is treated with isolation, quarantine, and supportive care.

An infected patient is separated from the rest of the population and given liquids to replace what is being lost. In addition to hydration, oxygen status and blood pressure are carefully maintained. This supportive therapy helps stabilize the patient until his or her own immune system is strong enough to take over.

What is the type of protein produced by the body to fight off infections?


When faced with a virus like Ebola, the body’s immune system will produce antibodies, large Y-shaped proteins, to identify and neutralize the pathogen. Antibodies target the virus for destruction by the immune system and remain in the blood, on constant guard against another attack.

As a possible preventative therapy against Ebola, the medical community looked to infection-fighting antibodies, isolated initially by immunizing mice with Ebola proteins but ultimately made in tobacco plants. A mixture of antibodies, an ‘antibody cocktail’, has been effective in protecting monkeys against Ebola in trial experiments, but has not been fully tested in humans.

With no other specific treatment available to them, doctors gave this experimental antibody cocktail to two American missionaries who contracted Ebola last summer in Africa. The results were promising, both patients survived.

This antibody therapy has not been approved for human use and still needs to go through clinical trials to prove its safety and effectiveness, but it is a promising step forward in fighting Ebola.

Last fall, an American healthcare worker infected with the Ebola virus was declared disease free until, months later, he was found to have Ebola in one of his organs. Which organ was it?

His eye

In September 2014, American doctor Ian Crozier contracted the Ebola virus while working for World Health Organization in Sierra Leone. Dr. Crozier was treated in an American hospital, declared disease free, and released.

Not long after his release, he experienced mild burning and light sensitivity in his eyes. Later his left eye lost its blue hue and became green and within two months he was readmitted.The Ebola virus was found to be active and replicating in Dr. Crozier’s eye.

The eye has protective biological properties that shield it from the immune system, but Ebola breeched that barrier. The virus damaged the pigmented cells thus changing his eye color.

Despite the presence of the virus in his eye, his tears and outer membrane tested negative for the virus. He was not at risk of infecting others around him. After treatment with anti-viral medication and steroids, eventually his eye returned to normal, and the Ebola virus was eradicated.

Which west African country has declared itself “Ebola free”?


The Ebola virus disease caused a deadly epidemic over the past year that frustrated a medical community determined to stop it. As of June 1, 2015, there have been over 11,000 deaths since the start of this recent epidemic but the true figure is believed to be much higher.

Finally, good news is beginning to surface: Liberia, the country hardest hit, was declared Ebola-free on May 9, 2015. It had been 42 days (twice the incubation time) since the last confirmed case was buried. The combination of a massive international response with Liberians changing their behavior slowed and eventually stopped the spread of Ebola.

Widespread funding given to efforts to help understand how Ebola works and is transmitted helped the world community learn to combat the disease.

Preliminary analyses suggested that in the recent outbreak, the virus changed at a faster rate than it had during previous outbreaks, which could make it more difficult to detect the virus, and to design effective specific therapies. However, new findings published in Science* report that the Ebola virus is not mutating as quickly as previously feared and that observed changes are unlikely to affect current diagnosis or vaccine efforts.

Several different vaccine strategies have shown success in non-human primates and some have started being tested in clinical trials with humans.

And now that the Ebola outbreak is over, the Confederation of African Football has cleared Liberia to host football games once again.

*Hoenen, T, el (2015) Mutation rate and genotype variation of Ebola virus from Mali case sequences. Science 348(6230):117-119

Which organ in the body is the least developed at birth?

The brain

Among all the organs in the human body, the brain is the most incomplete structure at birth. It is about 40% of the size it will be in adulthood.

At birth, cranium bones protecting the skull have spaces between them. These loosely attached bones help the baby slide more easily through its mother’s birth canal. Massive brain growth occurs in the first year of life.  These “soft spots” close during the first year as the bones fuse together.

In the evolutionary history of humans, brain size increased around the same time that the female reproductive system went through major changes.

What is the reason for the evolutionary shift in the size of the female pelvis?

Walking upright

Changes in human brain evolution may have been shaped by changes in the female reproductive system.

When our ancestors switched from walking on four legs to just two, the female body adapted to walking upright, altering the structure of the pelvis and making the birth canal significantly narrower.

Babies need to be born before they get too big for the birth canal. The skull of the brain evolved to be loosely fitting. At birth, the two frontal cranium bones can slide past one another compressing the head. The soft spot between them is called the anterior fontanelle,

Because the skull is not fully formed at birth, it allows for the massive increase in brain size, which occurs mostly in the first two years after birth. In contrast, chimpanzee brain growth occurs in the womb. Their anterior fontelles close around the time of birth.

During the course of human evolution, brain size has more than tripled and the structure of the skull is one of the reasons why.

Is a human baby altricial or precocial?


A human baby is altricial, meaning it is helpless at birth. Humans are born in an undeveloped state and require care and feeding by their parents.

Species that are active at birth are described as precocial (related to the word “precocious”). Precocial offspring can function semi-independently just after birth. Think of baby horses standing shortly after being born, dolphins swimming immediately after birth, and two-day old birds leaving the nest.

Animal species have evolved differently due to environmental pressures. When resources are plentiful, parents have time to nurture their young. When resources are scarce and predators are present, it is imperative that offspring quickly fend for themselves.

There are benefits and drawbacks to altricial and precocial births. Aided by the care and attention of their parents, the brains of altricial babies continue to grow as they mature. Precocial offspring, while having larger brains at birth, end up having smaller brains in relation to their body size.

What is the name for the nerve cells found in the brain?


Nerve cells, called neurons, are a core component of the nervous system and are housed mostly in our gray matter.

Neurons have an electrical field across their membrane that are used to transmit and process information. A typical neuron has a cell body with nucleus, dendrites, and an axon. Dendrites receive signals and axons transmit signals.

Neurons are responsible for thought, perception, motion, and control of bodily functions.

At what point in our lives do we have the most neurons?

  1. a) at birth
  2. b) during childhood and teenage years
  3. c) during adulthood

a, at birth

At birth, our brain is overflowing with neurons, more so than at any other point in our lives.  A baby brain is not just an adult brain that is small. It needs to be internally wired.

Neurons in the gray matter connect directly to nearby neurons, but to connect to neurons in another part of the brain or body, they send signals through the white matter. At birth only a very small percentage of neurons are connected to each other. As infants, information goes in and is absorbed by neurons, but doesn’t know where to go next.

Dramatic pruning of gray matter occurs in the last trimester and first year of life. As the brain grows, many neurons are lost when networks of connections are developed and refined.

How many neurons does the average adult brain have?

  1. a) 1 million
  2. b) 100 million
  3. c) 1 billion
  4. d) 100 billion

100,000 billion

Brain size is no reflection of intelligence. What matters is the number of neuron connections and maybe the way they connect. There are about 100,000 billion neurons in the human brain. Each neuron has to make connections with thousands of others.

Signals are sent through the axons of one cell and received through the dendrites of another. Information is passed in the form of electrical signals or by chemicals produced by the cell called neurotransmitters.

Many axons are coated in a fatty insulator-like substance called myelin to ensure the rapid acceleration of the signal. Messages take the most efficient route. As more signals are sent, patterns (memories) are established and organized into circuits.

What are the specialized points of contact between neurons where signals are transmitted and received?


There are specialized types of neurons. Some neurons detect external stimuli (light, sound, touch) or internal conditions (blood pressure, heart beat). Some interpret and analyze the incoming information. Others produce the physical response.

There is one axon on each neuron, but it may divide into many branches before ending at nerve terminals. Dendrites are covered with places for the axon to attach. The site of communication between the axon and the receiving cell is called a synapse.

As messages are continuously relayed throughout the brain and spinal cord, they create a regular predictable wiring plan. Repeated use strengthens synapse connections.

Only about half the neurons generated during development survive into adulthood. Initially, neurons are assigned specific characteristics. As they mature, they connect and work out specific routes that receive, analyze, and react to stimuli. Eventually these connections are adjusted and refined. Connections that are active and generating electrical currents survive. Those with little or no activity are pruned by the brain.

What do we call brain's ability to shape itself?


Plasticity (from the Greek word "plastos", meaning molded) is an organism’s ability to modify and adapt itself in response to its environment. Our brains are self-built. They are not static. They can change over the course of a lifetime and are shaped by one’s own particular experiences.

Brain plasticity underlies normal brain function such as our ability to learn and modify our behavior. Thinking, planning, and acting all influence the brain’s physical structure and functional organization.

Plasticity is strongest during childhood but continues to be a fundamental and significant lifelong property of the brain. Scientists studying brain plasticity explore the possibility that molding and rewiring brain circuitry could effectively treat addiction, learning disabilities, brain damage, and neurodegenerative diseases.

All animals have a nervous system with the exception of one. What animal has no nervous system?

A Sponge

Sponges are so sedentary they could be mistaken for plants. They spend most of their lives anchored to sediment or rocks. They have no nervous system and lack true tissues. They also have no digestive or circulatory systems.

But, like other animals, they are multicellular, heterotrophic, lack cell walls, and produce eggs and sperm cells. Sponges make specialized cells that generate water current and trap food particles. The constant flow of water through their porous bodies helps them to obtain food and oxygen and to remove waste.

Some types of sponges manufacture tough skeletal fibers while others produce more flexible filaments. Humans have used sponges as cleaning tools for thousands of years. In response to overfishing in the 1950s, most sponge-like materials these days are synthetic.

As the brain develops, how does it wire itself? From front to back? Or from back to front?

From back to front

When we are born, we have an overabundance of neurons. As we develop, neurons make connections to other neurons and to the brain stem. The brain begins to wire itself starting in the back with the structures that mediate our interaction with our environment: balance and coordination, vision, hearing, touch, and sense of space.

Connectivity slowly moves forward. The very last place to connect is the front lobe. The frontal lobe is responsible for higher cognitive skills such as problem solving, thinking, planning, organizing, behavior, and personality.

At what age is the brain considered to be fully mature?

Mid-twenties, around age 25.

Although many rights and privileges of adulthood are given by the age of 18, there is a growing body of science showing it takes several more years for the brain to fully mature.

Connectivity to and from the frontal lobe is the most complex and the last to fully develop. The frontal lobe manages judgment, insight, and impulse control. It continues to connect into the mid-twenties and perhaps even later.

The teenage brain is only about 80% of the way to maturity. The not-quite-finished frontal lobe helps explain mood swings, impulsiveness, risky behavior, and inability to concentrate that sometimes defines teenage behavior. Teenage years are a particularly vulnerable time for young brains that can last through college and beyond.

What do we call the act of switching between two or more cognitively complex things at the same time?


Multitasking is the practice of doing more than one task simultaneously. In this age of communication, some people think they can get more done by working on several projects at the same time.

Researchers believe that multitasking is a myth. It is virtually impossible for the brain to focus on more than one complex task at a time.

A person working on two things at once will actually take more time to complete them than if they had done them sequentially. Plus, due to lack of concentration, the work is prone to error. With gadgets continuously bombarding us with information, it has become harder to filter out distractions.*

Instead of working on two tasks at the same time, our brain switches back and forth very rapidly from task to task.

*Ophir, Nass, and Wagner (2009) Cognitive control in media multitaskers. PNAS USA 106(37):15583-15587.

Where did the term “multitasking” originate?

From computers

It is believed that the first time the word “multitask” appeared was in 1965 in a paper describing the capabilities of the IBM System/360.

In the computer engineering industry, multitasking refers to the ability of a computer to process several tasks at once. Computer multitasking in single-CPU processors involves time-sharing the processor. Only one task can be active at a time, but partial work on each task is rotated through many times a second. With multi-core computers, each CPU can perform a separate task simultaneously.

In addition to the skull, what else helps to protect the brain and spine from injury?

Cerebrospinal fluid

Cerebrospinal fluid (CSF) is a clear colorless liquid that bathes the brain and spinal cord.

The primary function of CSF is to cushion the brain within the skull and serve as a shock absorber for the central nervous system. It also circulates nutrients and chemicals filtered from the blood and removes waste products from the brain.

What type of cell is considered the “glue” for maintaining the structural integrity of the nervous system?

Glia cells

Glia (from the Greek word meaning “glue”) are the supporting cells for the central nervous system.

There are several different types of glia in the brain and spinal cord, including astrocytes, radial glia, oligodendrocytes, and Schwann cells. Each has a particular function but ultimately glia cells create an enclosed protected environment to help neurons perform their functions. They block toxic chemicals from blood, remove cellular waste from neurons, wrap around and insulate nerves, and help brain cells repair cellular damage.

Human brains have many more glia cells than neurons. In fact, it has been reported that humans have nine glia cells for every neuron.

Studies on Albert Einstein’s brain have shown that while it was surprisingly smaller and lighter than an average brain, it had a higher concentration of glia cells, particularly in the areas of the brain that control spatial and mathematical skills. Einstein worked at his highest efficiency because his brain was so well cared for by his glia cells.

What is the system of organs, nodes, ducts, and vessels that guards the body against infection and filters out cellular waste?

The lymphatic system

The main function of the immune system is to destroy invading pathogens and any toxic molecules they produce.The lymphatic system is a collection of tissues and organs, which together serve to drain the body of excess fluids and combat infections. Lymph is a colorless interstitial fluid that when in blood circulation is called plasma.

Once blood has delivered nutrients to cells, most of the fluid returns to the venous circulation through blood vessels.  The lymphatic system drains tissue spaces and cavities of fluid and ions that have not been recovered by the capillaries.

Lymph travels to the lymph nodes where disease organisms and cancer cells are filtered out and destroyed by the immune system. It is then returned to the blood.

What is the main type of cell found in the lymphatic system?


Lymphocytes are white blood cells found in the lymphatic system. Lymphocytes that complete their development in the bone marrow are called B cells, and those that mature in the thymus are called T cells.

Lymphocytes produce two types of immune response. They can either directly destroy infected body cells, cancer cells, or foreign tissue, or they can secrete defensive proteins called antibodies that bind to microbes to mark them for elimination.

Blood pumps through the cardiovascular system carrying nutrients and oxygen to tissues. The lymphatic system acts like a sewage system to whisk away waste.

What activity helps your brain to consolidate memories, and to form and repair neural connections?


It has long been known that sleep is essential for forming and consolidating memories. Additionally, it plays a central role in forming and pruning neural connections.

Sleep is also crucial to our brain’s physiological maintenance. Since the brain is outside the reach of the body’s lymphatic system, it was unclear how toxins were removed.

In an article published in 2013 in Science*, the authors contend that the brain has its own version of the lymphatic system. Since it relies on the glial cells in the brain, the authors proposed the name “glympathic” system for the networks of channels that clear out toxins with the watery cerebrospinal fluid.

Senior author, Maiken Nedergaard, and her team at the University of Rochester found that when they injected small fluorescent tracers into the cerebrospinal fluid (CSF) in mice, they entered the brain quickly and exited via specific predictable routes. In the awake state, CSF would flow only along the surface of the brain but as mice slept CSF could reach further into the brain. This process is too energy-expensive and the brain waits until bedtime so it can focus on it.

Sleep has a basic function. If not, something as dangerous as spending one-third of our life completely unaware and defenseless would have eliminated by evolution. It keeps our brain functioning well, and current research suggests that during sleep, our brain cleans itself.

*Xie, L, et al (2013) Sleep Drives Metabolite Clearance from the Adult Brain (2013) Science 342(6156):373-377.

How many hours of sleep is recommended for adults?

7-9 hours

Earlier this year, experts in the field of sleep reviewed current scientific literature and issued a public health statement. For the average adult, they recommend seven to nine hours of sleep per night.

Researchers found that sleeping less than seven hours per night, on a regular basis, is associated with health problems, including weight gain, hypertension, depression, and decreased longevity.  Individuals lacking proper sleep risk impaired immune function, increased errors, and had a greater risk of accidents behind the wheel and on the job.

The sleep panel also made it clear that behavioral, health, environmental, and genetic factors may affect how much sleep an individual may need.

How many hours does the average American adult sleep?

6.8 hours

In 2013, a Gallup Poll reported 59% of US adults met the recommendation of seven to nine hours of sleep per night.  The length of time Americans sleep is down more than one hour from 1942.

Even though Americans sleep less now than they ideally should, 56% say they get as much sleep as they need. Gallup also reported that 43% said they would feel better with more sleep.

The Center for Disease Control and Prevention has called insufficient sleep a public health epidemic.

A recent study in Current Biology reported on the sleeping habits of the world’s last remaining hunter-gatherers who live outside the reach of the modern world. How many hours per night do they sleep?

6 ½ hours

A recent article in Current Biology* reported the sleeping habits of three different tribes of hunter-gatherers in Tanzania, Namibia, and Bolivia. Because they have no electricity and their lifestyles have remained largely unchanged for thousands of years, it was thought they live as our ancestors lived before the advent of electric lighting.

The prevailing notion in sleep medicine is that humans evolved to go to bed as the sun went down. Dr. Jerome Siegel and his colleagues found no evidence of this. The hunter-gatherers, who slept outside or in crudes huts, stayed awake several hours past the setting of the sun. In a typical night, they slept just six and one half hours – less that the average American.

This paper has the ability to transform modern sleep medicine. Western society is thought to be sleep deprived due to modern distractions and pressing schedules, yet our sleep patterns are not so different from people living outside the technological age.

*Yetish, G, et al (2015) Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology 25(21):2862-2868.

Dr. Siegel reported that something other than the setting sun is prompting these hunter-gatherers to fall asleep. What is it?

Falling temperatures

In the same study*, Dr. Siegel reported that the three hunter-gatherer tribes almost always fell asleep as temperatures began to fall at night and would wake as the temperatures would rise again.

This phenomenon suggests that humans evolved to sleep during the coldest hours of the day, perhaps to conserve energy. The carefully modulated temperature of our homes is just another part of technological age, which is outside our ancestors’ experience.

*Yetish, G, et al (2015) Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology 25(21):2862-2868.

This week's answer:

What medical intervention mimics sleep?


The introduction of anesthetics has allowed both major and minor surgeries to be performed without pain that previously would have caused the patient severe or intolerable suffering.

Anesthesia causes a temporary state of relief from pain, either through a local intervention that targets one area of the body, or general that suppresses central nervous system activity.

General anesthesia is often thought of as putting the patient “to sleep” for the duration of the operation but researchers argue that this is not an accurate description of the process. They believe that under general anesthesia, the brain is in a drug-induced coma. A sleeping brain can be aroused and awakened, but the anesthetized brain is unresponsive, and requires careful monitoring.

Brown, Lydic, and Schiff (2010) General anesthesia, sleep, and coma. N Engl J Med 236:2638-2650.

Next week's question:

When was general anesthesia first used for surgeries?


Past questions and answers are in the trivia archives: 2012 / 2013 / 2014

Questions? Comments? Corrections? Contact Mary Leonard,

2015 The Trustees of the University of Pennsylvania