>> YOUR SKELETON IS THE STRUCTURE THAT PROTECTS AND DEFINES WHO YOU ARE.

IT'S A COMPLEX SYSTEM THAT HELPS YOU MOVE AND KEEPS YOU ALIVE.

WANT TO LEARN MORE ABOUT THE SKELETON?

SCIENTISTS ARE STANDING BY TO ANSWER YOUR QUESTIONS.

STAY TUNED.

"D4K" IS NEXT.

>> HI, I'M JOAN CARTAN-HANSEN.

WELCOME TO "D4K."

>>> TODAY WE'RE TALKING ABOUT SKELETONS.

BEFORE WE GO TO THE STUDIO TO ANSWER YOUR QUESTIONS, LET'S LEARN MORE.

YOUR BODY IS MADE UP OF 206 DIFFERENT BONES.

THE SMALLEST ARE THE BONES IN YOUR MIDDLE EAR.

AND THE LARGEST IS YOUR FEMUR, THE LONG BONE IN YOUR UPPER LEG.

PUT ALL THE BONES TOGETHER AND THEY MAKE UP THE SKELETAL SYSTEM.

>> THE SKELETON GIVES YOU STRUCTURE.

JUST LIKE THE WALLS OF A BOX.

>> HEY!

LET ME OUT!

>> IT PROTECTS YOUR INTERNAL ORGANS LIKE YOUR HEART AND LUNGS.

>> YOUR BONES ACT AS LEVERS FOR YOUR MUSCLES SO YOU CAN MOVE.

>> BONES AREN'T JUST DRY AND HARD.

THEY'RE LIVING TISSUE WITH DIFFERENT LAYERS.

THE OUTER SURFACE IS CALLED THE PERIOSTEUM.

IT'S A THIN MEMBRANE THAT CONTAINS NERVES AND BLOOD VESSELS THAT NOURISH THE BONE.

THE NEXT LAYER IS COMPACT BONE.

IT'S SMOOTH AND HARD LIKE AN ELEPHANT'S TUSK.

BUT IT HAS TINY CANALS THAT HAVE ARTERIES AND VEINS RUNNING THROUGH IT.

INSIDE THAT ARE MANY LAYERS OF CANCELLOUS BONE, WHICH LOOK LIKE A SPONGE.

AND IN THE MIDDLE IS THE BONE MARROW.

ITS JOB IS TO MAKE BLOOD CELLS.

ALL TOGETHER YOUR BONES WEIGH ABOUT 20 POUNDS, BUT THIS MULTILAYERED STRUCTURE GIVES THEM STRENGTH, WHILE KEEPING THEM LIGHT.

>> HOW STRONG ARE YOUR BONES?

A BONE IS SIX TIMES AS STRONG AS A STEEL BAR OF THE SAME WEIGHT.

BUT IF YOU FALL OR GET HIT JUST RIGHT YOU CAN STILL BREAK A BONE, SO BE CAREFUL.

>> THERE ARE SEVERAL DIFFERENT KINDS OF BONES.

LONG BONES, LIKE THE ONES IN YOUR LEGS, AND SHORT BONES, LIKE THE ONES IN YOUR HANDS, ACT AS LEVERS TO HELP YOU MOVE.

FLAT BONES, LIKE YOUR RIBS OR YOUR SKULL, ARE REALLY DESIGNED TO PROTECT INTERNAL ORGANS OR YOUR BRAIN.

SESAMOID BONES LIKE YOUR KNEE CAPS GET THEIR NAMES FROM THEIR SHAPE, AND IRREGULAR BONES LIKE YOUR VERTEBRAE DON'T IF IT IN OTHER CATEGORIES AND THEY TEND TO HAVE STRANGE PARTS JUTTING OUT THAT ALLOWS THEM TO CONNECT WITH MUSCLES AND OTHER BONES.

THE PLACE WHERE TWO BONES MEET IS CALLED A JOINT.

JOINTS ARE HELD TOGETHER BY LIGAMENTS, TISSUE LIKE A STRONG RUBBER BAND AND PROTECTED BY CARTILAGE, TISSUE THAT ACTS LIKE A CONSTITUTION, ABSORBING SHOCK.

MUSCLES ATTACH TO YOUR BONE AND ALL THE PIECES WORK TOGETHER TO HE YOU MOVE.

BUT NOT ALL JOINTS MOVE.

LIKE THE JOINTS IN YOUR SKULL.

>> 70% OF BONE MATERIAL IS ARE MADE UP OF DIFFERENT MINERALS LIKE CALCIUM, SO YOU HAVE TO EAT FOODS RICH IN MINERALS TO KEEP YOUR BONES HEALTHY.

>> SO YOUR SKELETON IS THE STRUCTURE OF YOUR BODY.

IT PROTECTS YOUR INTERNAL ORGANS, WORKS WITH YOUR MUSCLES TO HELP YOU MOVE, AND THE BONES ARE WHERE YOUR BLOOD CELLS ARE PRODUCED.

TAKE CARE OF YOUR SKELETON AND ALL YOUR BONES, AND THEY'LL TAKE CARE OF YOU.

AND JOINING ME NOW TO ANSWER YOUR QUESTIONS ABOUT SKELETONS AND THE SKELETAL SYSTEM ARE THREE GUESTS.

IN BOISE IS DR.

JEFFREY SHILT, DIRECTOR OF PEDIATRIC ORTHOPEDICS, THANK YOU FOR JOINING US.

ALSO JOINING US IS BENJAMIN DAVIS, MICROIMRAFT RESEARCHER.

AND JOINING US IN OUR MOSCOW STUDIO IS PROFESSOR JEFF SEEGMILLER, PROFESSOR OF MOVEMENT SCIENCE.

THANK YOU SIR, I APPRECIATE IT.

>> THANKS.

>> AND OF COURSE WE WANT TO HEAR FROM YOU.

CALL US HERE TOLL-FREE AT 1-800-973-9800, OR I'M US AT D4K@IDAHOPTV.ORG, OR TWEET US AT @D4KONIDAHOPTV.

AND REMEMBER, WHEN YOU SEND IN A QUESTION, YOU AND YOUR CLASS WILL HAVE A CHANCE TO WIN DVDs AND OTHER PRIZES.

LET'S GO TO OUR FIRST QUESTION, IT COMES FROM MRS.

SCHWEITZER'S FOURTH GRADE CLASS AT RIVERSIDE ELEMENTARY.

HOW LONG DOES IT TAKE FOR A LEG BONE TO BE REPAIRED?

DOCTOR, YOU BREAK YOUR BONE, HOW LONG DOES IT TAKE TO REPAIR?

>> FOR MOST OF US IT TAKES ABOUT SIX TO EIGHT WEEKS FOR THE BONES TO HEAL.

>> A SIMPLE BREAK, IF IT'S MORE COMPLICATED IT TAKES LONGER?

>> IT CAN, IF THERE'S MORE PIECES TO THE FRACTURE OR MORE BONE PIECES TO HE'LL, IT CAN TAKE LONGER.

AND AS YOU GET OLDER IT TAKES LONGER TO HEAL.

>> LET'S GO TO OUR FIRST VIDEO QUESTION.

THAT COMES FROM ADAM.

>> HI, MY NAME IS ADAM, MY QUESTION IS, WHY DOES BONES POP OUT OF THEIR SOCKETS.

>> WHY DO BONES -- PROFESSOR?

DO YOU WANT TO TAKE THAT ONE?

>> SURE.

USUALLY IT'S BECAUSE YOU'VE EXPERIENCED SOME FORCE THAT IS BEYOND THE CAPABILITIES OF THAT JOINT.

AND SO WHEN THAT HAPPENS, IT POPS OUT.

IT CAN'T HANDLE IT ANYMORE, AND WE SEE THAT SOMETIMES IN SPORTS INJURIES, AND THINGS LIKE THAT.

>> BUT IT DOESN'T JUST HAPPEN JUST OUT OF THE BLUE.

>> NO.

IT'S REALLY RARE.

>> OK.

LET'S GO TO OUR FIRST PHONE CALLER.

I THINK WE'VE GOT JUSTICE IN BOISE.

WHAT'S YOUR QUESTION?

>> Caller: MY QUESTION IS, WHAT IS THE STRONGEST BONE IN THE HUMAN BODY?

>> THAT'S A REALLY -- WE'VE BEEN TALKING ABOUT THAT.

THERE'S A DIFFERENCE OF OPINION ON THAT.

WE'LL ASK EVERYBODY AT THE TABLE WHAT THEY THINK.

DOCTOR, WHAT DO YOU THINK IS THE STRONGEST BONE IN THE BODY?

>> THERE'S NO SPECIFIC ANSWER TO THAT.

IT ACTUALLY DIFFERS AS YOU AGE, AND HOW MUCH STRESS IS FORMED ON EACH PART OF THE BODY.

SO I DON'T KNOW THAT THERE'S A SPECIFIC ANSWER FOR EVERYONE.

>> PROFESSOR, WHAT DO YOU THINK?

>> I HAVE MY BIASES.

I STUDY THE LOWER EXTREMITY, AND SO I LIKE TO THINK OF THE TALUS JUST BETWEEN THE FOOT AND THE LEG, AND IT'S ALWAYS HOLDING THINGS UP, AND HAS A LOT OF PRESSURE ON IT.

IT'S GOT TO RESIST A LOT OF FORCES.

BUT I THINK THE DOCTOR IS RIGHT, NOBODY HAS REALLY MEASURED WHICH ONE IS TRULY THE STRONGEST.

>> DO YOU HAVE AN OPINION?

>> I DON'T HAVE AN ANSWER, UNFORTUNATELY, LIKE EVERYBODY ELSE, BUT I THINK THAT YOU CAN KIND OF IMAGINE WHAT BONES ARE DOING THE MOST WORK IN YOUR BODY, AND THEN THAT'S ALSO GOING TO BE A QUESTION OF THE KIND OF WORK.

SO AS DR.

SEEGMILLER POINTED OUT, CERTAIN BONES WILL BAER A LOT OF WAIT -- BARE A LOT OF WEIGHT OR BEAR TENSION.

THE INTERESTING THING I THINK IS A LOT OF BONES ARE SORT OF JUST STRONG ENOUGH FOR THE AMOUNT OF WORK THEY'RE DOING, AND THEY'RE OFTEN BREAKING AND BEING REPAIRED CONSTANTLY BY THE CELLS IN YOUR BODY, AND IT ALSO IS GOING TO CHANGE HOW STRONG BONES ARE.

SO OVER TIME YOU CAN ACTUALLY MAKE CERTAIN BONES STRONGER, AND SO THAT WOULD PROBABLY DEPEND A LITTLE BIT ON A PARTICULAR PERSON'S BODY AND THE THINGS THEY'RE DOING, WHICH BONES IN THEM HAVE BEEN MADE STRONGER THAN MAYBE THEY HAVE IN OTHER PEOPLE.

>> WE DON'T -- WE THINK OF BONES AS BEING STATIC, BUT THEY'RE NOT.

BONES ARE LIVING, GROWING THINGS, AND YOU CAN STRENGTHEN YOUR BONES.

>> ABSOLUTELY.

THEY'RE VERY DYNAMIC.

A VERY IMPORTANT COMPONENT, WHEN YOU TALK ABOUT HOW STRONG A BONE IS, IT'S REALLY IN REFERENCE TO WHERE THE TRAUMA OR ENERGY IS DIRECTED TO THE BONE.

FOR INSTANCE, IF YOU TRY TO CRUSH A BONE, CERTAIN BONES ARE STRONGER IN THAT PARTICULAR INSTANCE, WHEREAS IF YOU TRIED TO BEND IT RIGHT IN THE MIDDLE IT DEMONSTRATES A DIFFERENT STRENGTH.

SO IT'S REALLY DEPENDENT UPON HOW YOU'RE TESTING HOW STRONG A BONE IS.

DEPENDING UPON WHERE YOU APPLY THAT PRESSURE.

>> PROFESSOR, YOU WANT TO JUMP IN?

>> YEAH, I JUST THINK THAT -- THEY HIT ON ALL OF THE DIFFERENT POINTS.

KIDS HAVE, YOU KNOW, ALL THESE CAPABILITIES TO STRENGTHEN THEIR BONES, AND IT DEPENDS ON THE BONE THAT YOU WANT TO STRENGTHEN, IF YOU WANT TO STRENGTHEN YOUR LOWER EXTREMITIES IN YOUR BACK, YOU WANT TO DO SOME TYPE OF EXERCISE THAT'S GOING TO STRENGTHEN THOSE SPECIFIC AREAS.

>> LET'S GO TO OUR NEXT PHONE CALL, THIS IS CASPER IN BOISE.

CASPER?

OR COOPER?

COOPER.

GO AHEAD.

>> Caller: WHY DO WE HAVE MARROW IN OUR BONES?

>> THE BONE MARROW PROVIDES THE SOURCE FOR ALL THE CELLS IN YOUR BODY THAT GO ON AND HELP PRODUCE OTHER TISSUES.

SO IT GIVES YOU ALL THE IMPORTANT CELLS IN YOUR BLOODSTREAM, BUT IT ALSO PROVIDES THE BASIS FOR CELLS THAT HELP PRODUCE THE TISSUES, ALL THE MUSCULOSKELETAL TISSUES YOU HAVE.

SO THE BONE MARROW IS SUPER IMPORTANT FOR ALL THOSE DIFFERENT REASONS.

>> LET'S GO TO OUR NEXT VIDEO QUESTION.

CASEY IS OUR NEXT VIDEO QUESTION.

>> HI, MY NAME IS CASEY, AND I GO TO DALTON ELEMENTARY.

MY QUESTION IS, WHAT IS BONE TISSUE MADE OF?

>> WE'VE TALKED ABOUT BONE MARROW.

IS THERE A DIFFERENCE BETWEEN MARROW AND TISSUE?

>> SURE.

ABSOLUTELY.

THE BONE MARROW WE THINK OF AS THE CELLS THAT ARE LITERALLY IN THE CENTER OF THE BONE.

AND THE BONE TISSUE MAY BE -- WE MAYBE REFERRING TO ACTUALLY THE OUTER SHELL OF THE BONE.

AND THAT'S DIFFERENT IN JUST AS WE WERE TALKING EARLIER ABOUT THE MINERALS AND THE CONSTITUENTS OF THAT, THE COLLAGEN IS THE MOST PREVALENT PROTEIN THAT MAKES UP BONE.

SO THE DIFFERENCE IN BETWEEN WHAT'S IN THE CENTER OF THE BONE AND THE OUTSIDE OF THE BONE IS QUITE VARIABLE AND DIFFERENT FOR SURE.

>> OK.

SYDNEY IS OUR NEXT VIDEO QUESTION.

LET'S TAKE A LOOK AND SEE WHAT SYDNEY HAS TO SAY.

>> MY NAME IS SYDNEY AND I GO TO DALTON ELEMENTARY.

HOW DO KIDS LIKE ME SPRAIN THEIR ANKLES?

>> PROFESSOR, LET'S TOSS THAT ONE YOUR WAY.

>> WELL, ANKLES, YOU KNOW, WHEN THEY GET SPRAINED, YOU END UP HURTING A LIGAMENT.

AND LIGAMENTS ARE WHAT HOLD THE BONES TOGETHER.

WHAT HAPPENS IS SOMETIMES YOU LAND ON SOMETHING AND YOU'RE NOT EXPECTING IT, AND SO THAT JOINT ROLLS FARTHER THAN IT WAS EXPECTED TO ROLL, AND IT PUTS TOO MUCH STRESS ON THAT LIGAMENT.

AND THEN THAT LIGAMENT GETS HURT.

AND SO THAT'S USUALLY HOW WE END UP DOING IT, WE'RE NOT EXPECTING IT.

AND IT ROLLS TOO FAR.

>> KATHERINE IN MRS.

SCHWEITZER'S FOURTH GRADE CLASS WOULD LIKE TO KNOW, WHICH BONE IN YOUR BODY IS THE MOST IMPORTANT?

THAT'S ANOTHER KIND OF UP FOR DEBATE, WE'LL ASK ALL THREE OF YOU.

WE'LL START WITH YOU, PROFESSOR, WHAT'S THE MOST IMPORTANT BONE?

>> WELL, I LIKE TO HEAR, SO I REALLY LIKE MY OSSICLES, THE REALLY SMALL BONES THAT HAVE SUCH A MAJOR IMPACT.

BUT I GUESS THAT WOULD BE DEBATABLE.

YOU NEED TO LIVE TOO, SO -- >> I THINK THAT'S A REALLY GOOD QUESTION.

SOMETHING WITH A LOT OF POTENTIAL ANSWERS.

THE CASE COULD PROBABLY BE MADE THAT CERTAIN PROTECTIVE BONES, PARTICULARLY THOSE LIKE YOUR SKULL AND YOUR VERTEBRAL COLUMN, PROTECTING YOUR CENTRAL NERVOUS SYSTEM ARE VERY IMPORTANT, BECAUSE THEY ALLOW TO YOU DO ALL THE COMPLICATED THINGS MANY OF US DO FROM THE STANDPOINT OF YOUR NERVOUS SYSTEM, KEEPING THOSE INTACT.

BUT AT THE SAME TIME, ALL OF THOSE OTHER BONES ACTING AS LEVERS ALOCAL -- ALLOW TO YOU MOVE AND DO OTHER COMPLICATED THINGS.

SO I GUESS IT'S REALLY JUST A QUESTION OF PRIORITIES.

WHAT DO YOU LIKE TO DO THE MOST?

IF YOU LIKE TO DANCE, YOU MIGHT BE A BIG FAN OF THE FEMUR AND THE HIP SOCKET.

IF YOU'RE SOMEBODY WHO IS MORE INTERESTED IN THE SPELLING BEE, YOU MIGHT BE APPRECIATIVE OF YOUR SKULL FOR KEEPING YOUR BRAIN INTACT.

>> DOCTOR, DO YOU HAVE A FAVORITE BONE?

>> I CAN'T IMPROVE UPON THAT ANSWER.

THAT'S REALLY FANTASTIC.

IT REALLY DEPENDS UPON WHAT FUNCTION YOU'RE TALKING ABOUT.

I COULDN'T SAY IT ANY BETTER.

IF MOVEMENT IS IMPORTANT TO YOU, OBVIOUSLY ALL THE BONES THAT ACT AS LEVERS FOR THOSE MUSCLES ARE SUPER IMPORTANT.

BUT YOU'RE PARALYZED IF THE SPINAL CORD IS INJURED, AND WHAT PROTECTS THE SPINAL CORD IS THE VERTEBRAL COLUMN.

CERTAINLY A LOT OF PEOPLE WOULD THINK -- >> CERTAIN BRAYS ARE IMPORTANT.

>> ABSOLUTELY.

>> AND OUR DENTIST WOULDN'T WANT YOU TO FORGET YOUR TEETH ARE BONES TOO, AND THEY'RE VERY IMPORTANT.

>> THERE YOU GO.

SEE, THERE'S LOTS OF CHOICES ON THE MOST IMPORTANT BONE.

LET'S GO TO A QUESTION FROM MRS.

HUNT'S FOURTH GRADE CLASS AT CYNTHIA MANN ELEMENTARY.

GABE WOULD LIKE TO KNOW, HOW DOES THE SKULL MOVE?

WE TALKED ABOUT THE SKULL HAS JOINTS, BUT IT DOESN'T MOVE A GREAT DEAL.

CAN YOU TELL US ABOUT THE SKULL?

>> SURE.

SO THE SKULL BONES THEMSELVES MOVE VERY LITTLE.

AND WE CALL THE JOINTS ON THE SKULL SUTURES, AND THEY'LL MOVE JUST -- THEY MOVE IN RESPONSE TO PERHAPS TRAUMA, OR TO SWELLING IN THE BRAIN, BUT IT'S A VERY, VERY SMALL AMOUNT OF MOTION.

BUT IF YOU'RE REFERRING TO HOW DOES THE HEAD MOVE IN RELATION TO THE REST OF YOUR BODY, THE TWO MOST -- THE TWO BONES CLOSEST TO THE SKULL ON TOP OF THE SPINE ALLOW FOR ALL THE ROTATION, AND THE FLEX AND EXTENSION THAT WE SEE, OR THE UP AND DOWN MOVEMENT.

SO THAT'S REALLY WHAT ALLOWS US -- IT'S A SPECIAL RELATIONSHIP BETWEEN THOSE TOP TWO SPINAL BONES AND THE SKULL TO ALLOW FOR ALL THE MOVEMENT THAT WE'RE ABLE TO ACHIEVE.

>> THE BODY IS A PRETTY MAG MAGNIFICENT -- THE STRUCTURE OF THE SKELETON IS AMAZING.

ALL THE THE PARTS WORK TOGETHER IN DIFFERENT WAYS TO CREATE THE WHOLE YOU.

I THINK IT'S COOL.

I WANT TO ASK YOU ABOUT YOUR RESEARCH IN MICROGRAVITY.

YOU WORKED WITH NASA, WHY WOULD YOU -- WHY WOULD WE WANT TO THINK ABOUT BONES OF ASTRONAUTS IN SPACE?

>> A LITTLE BIT EARLIER WE TALKED ABOUT HOW BONES ARE DYNAMIC AND HOW THEY CAN CHANGE DURING THE COURSE OF YOUR LIFE.

AND A LOT OF TIME THAT'S -- THE VAST MAJORITY OF THE TIME THAT'S A GOOD THING, IT ALLOWS US TO HAVE BONES THAT ARE VERY STRONG AND SHAPED VERY WELL TO DO THE THINGS THEY NEED TO DO WITHOUT BEING OVERLY HEAVY.

SO THEY DON'T NEED TO BE JUST COMPLETELY SOLID MINERAL, BECAUSE THEN WE'D HAVE TO HAVE MORE MUSS TOL CARRY THEM AROUND.

THEY'RE THAT THE PERFECT POINT, AND THAT HAPPENS BECAUSE CELL TYPES IN YOUR BONES, SOME OF THEM EAT UP THE BONE AND SOME OF THEM MAKE NEW BONE.

AND THEY DO THAT IN RESPONSE TO CUES FROM THEIR ENVIRONMENT.

THEY TAKE THAT INFORMATION THAT DETERMINES WHERE THEY'RE GOING TO PUT DOUBT MINERALIZED BONE.

THE PROBLEM IS THAT WHEN ASTRONAUTS GO INTO MICROGRAVITY, THE INFORMATION THAT THEIR BONE CELLS ARE RECEIVING IS VERY DIFFERENT FROM THE INFORMATION THAT THOSE BONE CELLS WOULD BE RECEIVING ON EARTH, BECAUSE IN MICROGRAVITY AS THE NAME IMPLIES, THERE'S MUCH LESS GRAVITY, AND IT REALLY CHANGES THE WAY THAT THE BONES EXPERIENCES THE FORCES ON THE BODY.

AND WHAT TENDS TO HAPPEN IS THAT WHEN YOU HAVE INCREASED AMOUNTS OF FORCES YOU TEND TO GET MORE BONE AND THE OPPOSITE BEING WHEN YOU DECREASE AMOUNTS OF FORCES, YOU TONED LOSE BONE.

AND WHAT HAS HAPPENED IN ASTRONAUTS IS THAT THEY TEND TO LOSE BONE, AND THAT'S DANGEROUS FOR THEM FOR A NUMBER OF REASONS.

ONE IS THAT UPON RETURNING TO EARTH WHERE THEY'RE THEN GOING TO BE EXPOSED TO MORE FORCES THAN THEY -- THEIR BODY WAS ADAPTING TO, SAY OTS INTERNATIONAL SPACE STATION, THEY MIGHT BE AN IN-- AT AN INCREASED RISK FOR FRACTURE.

ALSO THE WORK THEY'RE DOING IN SPACE IS OFTEN QUITE ACTIVE AND QUITE DANGEROUS, AND IF THEY'RE INJURED VERY FAR AWAY FROM HOME IT'S DIFFICULT TO HELP THEM.

SO THE RESEARCH THAT WE DO IS TO TRY AND UNDERSTAND A LITTLE BIT ABOUT HOW THE CELLS IN BONE SENSE THE INFORMATION AND HOW THEY CHANGE -- TURN THAT INFORMATION INTO THE ACTIVITIES OF BUILDING OR BREAKING DOWN BONES.

SO THAT MAYBE WE CAN BY UNDERSTANDING THAT DO THINGS LIKE PREPARE BETTER EXERCISES FOR THEM, OR FOR EXAMPLE GIVE THEM CERTAIN PHARMACEUTICALS THAT CAN INFLUENCE THE BEHAVIOR SO THAT MAYBE IN ONE SENSE YOU CAN IMAGINE WE MIGHT WANT TO TRICK THEIR BONES INTO NOT RECOGNIZING THAT THEY'RE IN A REDUCED GRAVITY ENVIRONMENT SO THAT THEY DON'T LOSE BONE IN THAT TIME, SO, FOR EXAMPLE, IF THEY'RE ON A MISSION TO MARS, THEY CAN GO INTO MICROGRAVITY, GO THROUGH THAT LONG VOYAGE, AND ARRIVE ON THE PLANET AGAIN THAT HAS GRAVITY AND NOT BE IN DANGER OF BEING INJURED.

>> OK.

SOUNDS LIKE GREAT RESEARCH.

>> IT'S A LOT OF FUN.

>> LET'S GET BACK TO SOME MORE QUESTIONS FROM EMAIL, FROM McDONALD ELEMENTARY, THE QUESTION, WHAT'S THE SMALLEST BONE IN THE HUMAN BODY IN MICHAEL WOULD LIKE TO KNOW THAT.

>> THE SMALLEST BONE IN THE BODY IS ONE IN THE EAR CALLED THE STAPES.

IT'S CONNECTED TO THE REST OF THE BODY THROUGH THE SMALLEST MUSCLE.

>> NITS YOUR EAR.

THERE YOU GO.

HOW MANY BONES ARE THERE IN AN AVERAGE 10-YEAR-OLD GIRL'S BODY?

>> WELL, WE HAVE 206 BONES, BUT BEFORE WE'VE FULLY MATURED, SOME OF THOSE BONES ARE ACTUALLY IN PARTS, HELD TOGETHER BY CARTILAGE.

SO SOMETIMES THEY MIGHT EVEN COUNT IT AS MORE BONES.

SO YOUNGER CHILDREN MAY HAVE MORE BONES THAN ADULTS.

>> JAKE IN MRS.

CHILDRESS'S CLASS WOULD LIKE TO KNOW, DO TEETH HAVE MORE CALCIUM THAN OTHER BONES?

>> I WISH I KNEW THE ANSWER TO THAT.

>> WE'LL HAVE TO FIND THAT ONE OUT FOR YOU.

JAKE, WE'LL -- I'LL CALL MY DENTIST AND ASK MY DENTIST.

LET'S GO TO OUR NEXT VIDEO QUESTION.

I BELIEVE IT COMES FROM KATY.

>> MY NAME IS KATY, AND I GO TO DALTON ELEMENTARY SCHOOL.

MY QUESTION IS, WHY DO PEOPLE GET A CONCUSSION WHEN THEY GET HIT ON THE HEAD?

>> PROFESSOR, HOW DO YOU GET A CONCUSSION, AND WHAT IS A CONCUSSION?

>> WELL, A CONCUSSION USUALLY HAS TO DEAL WITH SOME TYPE OF TRAUMA TO THE BRAIN THAT'S INSIDE OF THE BONE.

IT'S BEING PROTECTED BY THE BONES.

AND SO USUALLY WHAT HAPPENS IS THAT FORCE GOES ALL THE WAY IN AND THE BRAIN KIND OF SMASHES UP AGAINST THE BONE SOMETIMES.

AND SO GETTING THAT BRAIN SHAKEN AROUND INSIDE OF THAT PROTECTIVE CAVITY IS USUALLY HOW WE GET TRAUMA THAT WE UNDERSTAND EVER END UP CALLING A CONCUSSION.

>> ROB FROM GRACE JORDAN ELEMENTARY WOULD LIKE TO KNOW, WHY ARE SKELETONS I HOLD MUCH BIGGER THAN YOUR ACTUAL EYES?

THE EYE SOCKET, WHY ARE THEY SO MUCH BIGGER THAN YOUR EYES?

>> THEY'RE PROBABLY NOT ACTUALLY LARGER, BUT WHAT YOU SEE OF THEM APPEARS LARGER.

THE EYES THEMSELVES IF IT NICELY IN THE SOCKET, AND THERE'S OTHER TISSUE THAT FITS THERE AS WELL.

IN A SKELETON YOU'RE SEEING THE EYE SOCKET, AND WE'RE COVERING ALL THAT EYE SOCKET UP BY ALL THE SOFT TISSUE AND EVERYTHING ELSE WE HAVE.

SO IT MAY APPEAR IT'S LARGER IN A SKELETON, BUT IN FACT THEY'RE EXACTLY THE SAME AS THEY ARE IN LIFE, PEOPLE AS WELL.

THEY'RE JUST COVERED WITH TISSUE.

>> YOUR EYES ARE REALLY -- MAYBE THE EYEBALLS ARE BIGGER THAN YOU THINK?

>> THEY'RE A LOT BIGGER.

>> JOSH WOULD LIKE TO KNOW, DO -- WHEN DO KIDS' BONES STOP GROWING?

>> GOOD QUESTION.

IT'S DIFFERENT FOR EVERY CHILD.

MOST GIRLS TEND TO GROW AND GROW MORE QUICKLY, AND THEN THEY TEND TO STOP GROWING ALSO EARLIER THAN BOYS DO.

MOST GIRLS WE THINK STOP GROWING AROUND 14 YEARS OF AGE, AND BOYS AROUND 16 YEARS OF AGE.

BUT THOSE ARE APPROXIMATES, AND EVERYONE, YOU HAVE KIDS THAT GROW QUICKLY AND KIDS THAT GROW LATER, SOMETIMES WE CALL THEM LATE BLOOMERS.

AND IT'S SIMPLY A DIFFERENCE IN THE VARIATION OF EACH INDIVIDUAL.

>> I GREW A COUPLE INCHES IN HIGH SCHOOL, SO THAT WAS A LATE FOR A GIRL?

>> IT IS A LITTLE LATER FOR A GIRL.

>> I HAD TO GET TALLER THAN MY BROTHER.

LET'S GO TO OUR NEXT VIDEO QUESTION, THAT'S DYLAN.

>> HI, MY NAME IS DYLAN.

I GO TO DALTON ELEMENTARY AND MY QUESTION IS, HOW DOES THE KNEE STAY TOGETHER?

>> SO PROFESSOR, HOW DOES -- WHEN YOU LOOK AT YOUR KNEE, HOW IS IT STAYING TOGETHER?

>> YEAH.

WELL, THIS IS A GOOD ONE, BECAUSE IT DOESN'T HAVE THE -- THE BONES DON'T HAVE A REALLY BIG SOCK THEAT THEY SIT TOGETHER N SO THIS REALLY RELIES ON TENDONS, AND LIGAMENTS, AND A JOINT CAPSULE THAT ARE ALL PART OF THIS SYNOVIAL JOINT, THE DISWHRIENT HAS FLUID INSIDE OF IT.

THAT'S ALL HELD TOGETHER BY THOSE OTHER STRUCTURES.

>> OK.

AND LET'S GO TO A CALLER, WE HAVE COLE.

>> Caller: HOW DOES THE BONE GROW?

>> HOW DOES THE BONE GROW?

WE'VE TALKED ABOUT HOW TO HELP THE BONES GROW, BUT HOW DO BONES ACTUALLY GROW?

>> SURE.

I THINK THE PROFESSOR WAS SAYING EARLIER THAT IN MOST BONES THEY HAVE A GROWTH PLATE, AND THAT GROWTH PLATE IS COMPOSED OF DIFFERENT CELLS CALLED CARTILAGE, AND THE CARTILAGE AS IT MULTNOMAH PULITZER PRIZE OR DIVIDES, WIDENS, AND AS IT'S WIDENING IT SLOWLY BECOMES CALCIFIED AT ITS ENDS, AND THAT'S -- IT ADDS ADDITIONAL BONE, AND THAT'S HOW THE BONE ESSENTIALLY GROWS, BY ADDING CALCIUM TO THE CARTILAGE CELLS.

>> A GOOD REASON TO DRINK YOUR MILK.

>> DRINK YOUR MILK.

>> LET'S GO TO OUR NEXT VIDEO QUESTION FROM MORGAN.

>> HI, MY NAME IS MORGAN, I GO TO DALTON ELEMENTARY.

MY QUESTION IS, ARE THERE ANY BONES THAT CAN'T BE HEALED WHEN YOU BREAK THEM?

>> DOCTOR, ANY BONES THAT CAN'T HEAL?

>> MOST BONES CAN HAVE THE ABILITY TO HEAL.

BUT CERTAINLY SOME OF THEM ARE LESS LIKELY OR MORE LIKELY NOT TO HEAL.

THERE'S CERTAIN BONES IN YOUR WRIST, SIMILAR SUCH AS THE SCAFFOID, IT DOESN'T LIKE TO HEAL SOMETIMES.

DIFFERENT BONES IN YOUR HIP, FOR INSTANCE, THE FEMORAL NECK DOESN'T LIKE TO HEAL SOMETIMES AS YOU GET OLDER.

THERE ARE MANY BONES THAT HAVE A TENDENCY NOT TO HEAL AS OTHERS, BUT MOST BONES HAVE THE POTENTIAL TO HEAL.

>> HOW ABOUT THE BONES IN YOUR EAR?

>> AN UNCOMMON THING I'VE EVER RUN ACROSS, BUT ALL BONE MATERIAL HAS THE ABILITY -- IT'S ONE OF THE FEW TISSUES IN OUR BODY THAT WILL HEAL WITHOUT SCAR TISSUE.

SO, FOR INSTANCE, YOU HAVE A MUSCLE AND YOU HAVE A TEAR OR BRUISE, IT FORMS SCAR TISSUE, WHEREAS THE BONE WILL HEAL AND HEAL WITHOUT SCARRING.

ALMOST ALL BONES CAN HEAL, OR POTENTIALLY HEAL.

>> LET'S GO TO OUR NEXT QUESTION, IT COMES I BELIEVE FROM BRADY.

>> HI, MY NAME IS BRADY.

I GO TO DALTON ELEMENTARY, AND MY QUESTION IS, HOW DOES BLOOD GET IN YOUR BONE?

>> THAT'S PART OF THE BONE WE DON'T THINK ABOUT, THAT THAT'S WHERE THE BLOOD COMES FROM.

PROFESSOR, DO YOU WANT TO TALK A LITTLE BIT ABOUT THAT?

>> SURE.

WE HAVE ALL THESE BLOOD VESSELS THAT ARE ACTUALLY GOING TO THE BONES, AND THEN THAT BRANCHES OFF AND ACTUALLY GOES THROUGH ALL PARTS OF THE BONE.

AND SO THAT'S THAT CONTRIBUTING FACTOR THAT REALLY HELPS BONE TO HEAL WHEN IT GETS INJURED.

IF THE BLOOD VESSELS GET INJURED, THEN IT MAKES IT DIFFICULT FOR THAT BONE TO HEAL SOMETIMES.

BUT YEAH, WE HAVE BLOOD VESSELS GOING EVERYWHERE.

>> BRADY SENT AN EMAIL IN, WHY DO WE NEED BONES?

WHY DO YOU THINK YOU NEED BONES?

>> WELL, JUST START WITH ONE, I THINK WE TALKED ABOUT IN THE LAST QUESTION, YOU NEED A PLACE TO MAKE ALL OF THE CELLS WE NEED THE BONE MARROW.

>> PROFESSOR Y. DO YOU NEED BONE?

>> I LIKE TO MOVE.

SO WE NEED BONES TO MOVE.

>> DOCTOR?

>> CERTAINLY THE OTHER IMPORTANT ONE IS THE PROTECTIVE MECHANISM IT PROVIDES FOR YOUR BRAIN AND OTHER TISH EXPIEWS SPINAL CORD.

>> LOTS OF GOOD REASONS TO TAKE CARE OF YOUR BONE.

I WANT TO ASK YOU WHY YOU DECIDED TO STUDY BONES AS A JOB.

DOCTOR, WHY DID YOU WANT TO BECOME AN ORTHOPEDIST AND TAKE CARE OF KIDS' BONES?

>> IT'S A VERY SATISFYING FIELD.

WE REALLY GET TO TAKE CARE OF PEOPLE WHO HAVE A VERY DISTINCT PROBLEM, AND THEN WE FIX AND IT MAKE THEM BETTER.

IT HAPPENS OVER A RELATIVELY SHORT PERIOD OF TIME.

SO IT'S A VERY SATISFYING, GRATIFYING FIELD TO GO INTO.

>> PROFESSOR, HOW ABOUT YOU?

WHY DID YOU WANT TO STUDY MOVEMENT IN SIGH ?ENS.

>> WHEN I WAS IN FOURTH GRADE, I FLEW OUT OF A SWING SET BACKWARDS AND BROKE MY ARM.

AND EVER SINCE THEN, I WAS CURIOUS ABOUT BONES.

AND AS AN ATHLETIC TRAINER I SAW A LOT OF PEOPLE GET INJURED, AND I WANTED TO UNDERSTAND HOW TO PREVENT INJURIES AND UNDERSTAND THIS MUSS SCHAL SKELETAL SYSTEM.

THAT HELPED SHAPE MY DIRECTION, MY CAREER.

>> HOW ABOUT YOU?

WHY DID YOU WANT TO STUDY BONE?

>> I THINK I REALLY BECAME INTERESTED IN BONES WHEN I STARTED TO REALIZE, AS YOU POINTED OUT EARLIER, THAT THE BONES ARE VERY DYNAMIC, AND I THINK I ALWAYS THOUGHT, UNLIKE A LOT OF YOUR STUDENTS, I THOUGHT IT -- I THOUGHT THAT BONES WERE LIKE ROCKS IN YOUR BODY, THAT THEY WERE VERY STATIC AND BORING, AND WHEN I CAME TO UNDERSTAND ALL OF THE DIFFERENT KINDS OF BIOLOGY THAT ARE GOING ON WITHIN BONES, AND THINGS LIKE WITH THEM PROCESSING INFORMATION, IN A SIMILAR WAY TO THE WAY PEOPLE THINK ABOUT MAYBE THE NERVOUS SYSTEM, IT JUST BECAME A REALLY INTERESTING THING TO ME AND I WANTED TO LEARN MORE ABOUT IT.

>> AND IF YOU SOMEDAY WANT TO BE A SCIENTIST WHO WORKS WITH BONES, WHAT SORT OF THINGS SHOULD YOU STUDY IN SCHOOL?

>> OH, ALL THE BIOLOGY COURSES ARE REAL IMPORTANT, ANATOMY.

THOSE ARE TWO REAL IMPORTANT AREAS TO STUDY.

>> PROFESSOR?

>> YEAH, WOULD I AGREE WITH THAT.

GET A GOOD ANATOMY CLASS, BECAUSE THAT WILL TEACH YOU A LOT ABOUT IT, AND THE BIOLOGY WILL HELP YOU GET -- GAIN THE UNDERSTAND OF WHAT IT'S ALL MADE OF.

>> I WOULD SAY IT'S PROBABLY GOOD FOR PEOPLE'S INTEREST IN UNDERSTANDING A PRACTICAL WAY TO KEEP PLAYING GAMES AND PLAYING SPORTS AND THINK ABOUT THEIR BODY, IN THOSE CONTEXTS, AND ALSO THEN TO GO DOWN TO THE TINY LEVEL AND THINK ABOUT MOLECULES.

PAY ATTENTION IN CHEMISTRY AND PHYSICS AS WELL.

>> WE HAVE RUN OUT OF TIME.

I'D LIKE TO THANK OUR GUESTS, PROFESSOR JEFF SEEGMILLER, DR.

JEFFREY SHILT AND BENJAMIN DAVIS.

THANK YOU FOR JOINING US.

JOIN US NEXT TIME, GO TO OUR WEBSITE TO LEARN MORE ABOUT SKELETONS.

CHECK IT ALL OUT AT IDAHOPTV.ORG IDAHOPTV.ORG.

LAST MONTH'S WINNER WAS EMMA FROM JENNIFER HUNT'S CLASS AT CYNTHIA MANN ELEMENTARY AND HARRISON FROM HELEN SCHWEITZER'S CLASS AT RIVERSIDE ELEMENTARY.

WHEN YOU SEND IN A QUESTION YOU AND YOUR CLASS ARE ELIGIBLE FOR OUR CONTEST.

WIN DVDs, LOTS OF OTHER PRIZES JUST BY SENDING IN A QUESTION.

NEXT MONTH WE'LL TALK ABOUT THE MOON.

SO SEND YOUR QUESTIONS IN NOW.

Captioning performed by LNS Captioning www.LNScaptioning.com