Welcome to The Visible Embryo

Home-- -History-- -Bibliography- -Pregnancy Timeline- --Prescription Drugs in Pregnancy- -- Pregnancy Calculator- --Female Reproductive System- -Contact
 

Welcome to The Visible Embryo, a comprehensive educational resource on human development from conception to birth.

The Visible Embryo provides visual references for changes in fetal development throughout pregnancy and can be navigated via fetal development or maternal changes.

The National Institutes of Child Health and Human Development awarded Phase I and Phase II Small Business Innovative Research Grants to develop The Visible Embryo. Initally designed to evaluate the internet as a teaching tool for first year medical students, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than one million visitors each month.

Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

WHO International Clinical Trials Registry Platform


The World Health Organization (WHO) has created a new Web site to help researchers, doctors and
patients obtain reliable information on high-quality clinical trials. Now you can go to one website and search all registers to identify clinical trial research underway around the world!



Home

History

Bibliography

Pregnancy Timeline

Prescription Drug Effects on Pregnancy

Pregnancy Calculator

Female Reproductive System

Contact The Visible Embryo

News Alerts Archive

Disclaimer: The Visible Embryo web site is provided for your general information only. The information contained on this site should not be treated as a substitute for medical, legal or other professional advice. Neither is The Visible Embryo responsible or liable for the contents of any websites of third parties which are listed on this site.
Content protected under a Creative Commons License.

No dirivative works may be made or used for commercial purposes.

Return To Top Of Page
Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
CLICK ON weeks 0 - 40 and follow along every 2 weeks of fetal development
Google Search artcles published since 2007
 
 

Home | Pregnancy Timeline | News Alerts |News Archive Sep 17, 2013

 

Biologically formed  'cog wheels' connecting the hind legs of the plant hopper, Issus.







Only the nymph stage uses leg "gears" to jump. Moving its gear box
within 30 'microseconds' of each other — equal to a millionth of
a second — rounded corners prevent 'teeth' from shearing off.


WHO Child Growth Charts

 

 

 

'Mechanical gears' seen in hopping insect for the first time

The juvenile Issus - a plant-hopping insect found in gardens across Europe - has hind-leg joints with curved cog-like strips of opposing 'teeth' that mesh, rotating like mechanical gears to synchronise the animal's legs when it launches into a jump.

This finding demonstrates that gear mechanisms previously thought to be solely man-made have an evolutionary precedent. Scientists believe this is the "first observation of mechanical gearing in a biological structure."

Through a combination of anatomical analysis and high-speed video capture of normal Issus movements, scientists from the University of Cambridge have been able to reveal these functioning natural gears for the first time.

Their findings are reported in the latest issue of the journal Science.


The gears in the Issus hind-leg bear a remarkable engineering resemblance to those found on every bicycle, as well as inside every car gear-box.


Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made bike gears – essentially a shock-absorbing mechanism to stop teeth from shearing off.

The gear teeth on the opposing hind-legs lock together like those in a car gear-box, ensuring almost complete synchronicity in leg movement - the legs always move within 30 'microseconds' of each other, with one microsecond equal to a millionth of a second.

This is critical for the powerful jumps that are this insect's primary mode of transport, as even miniscule discrepancies in synchronisation between the velocities of its legs at the point of propulsion would result in "yaw rotation" - causing the Issus to spin hopelessly out of control.


"This precise synchronisation would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required.

"By developing mechanical gears, the Issus can just send nerve signals to its muscles to produce roughly the same amount of force - then if one leg starts to propel the jump the gears will interlock, creating absolute synchronicity.

"In Issus, the skeleton is used to solve a complex problem that the brain and nervous system can't. This emphasises the importance of considering the properties of the skeleton in how movement is produced."

Professor Malcolm Burrows, lead author, Department of Zoology, Cambridge University

 

"We usually think of gears as something that we see in human designed machinery, but we've found that that is only because we didn't look hard enough,

"These gears are not designed; they are evolved - representing high speed and precision machinery evolved for synchronisation in the animal world."

co-author, Gregory Sutton, now at the University of Bristol

 


Interestingly, the mechanistic gears are only found in the insect's juvenile – or 'nymph' – stages, and are lost in the final transition to adulthood. These transitions, called 'molts', are when animals cast off rigid skin at key points in their development in order to grow.

It's not yet known why the Issus loses its hind-leg gears on reaching adulthood. The scientists point out that a problem with any gear system is that if one tooth on the gear breaks, the effectiveness of the whole mechanism is damaged. While gear-teeth breakage in nymphs could be repaired in the next molt, any damage in adulthood remains permanent.

It may also be down to the larger size of adults and consequently their 'trochantera' - the insect equivalent of the femur or thigh bones. The bigger adult trochantera might allow them to can create enough friction to power the enormous leaps from leaf to leaf without the need for intermeshing gear teeth to drive it, say the scientists.

Each gear strip in the juvenile Issus was around 400 micrometres long and had between 10 to 12 teeth, with both sides of the gear in each leg containing the same number – giving a gearing ratio of 1:1.


Unlike man-made gears, each gear tooth is asymmetric, curved towards the point where the cogs interlock.

Man-made gears use a symmetric shape to work in both rotational directions, whereas the Issus gears only power one way to launch the animal — forward.


While there are examples of apparently ornamental cogs in the animal kingdom - such as on the shell of the cog wheel turtle or the back of the wheel bug - gears with a functional role either remain elusive or have been rendered defunct by evolution.

The Issus is the first example of a natural cog mechanism with an observable function, say the scientists.

Abstract
Gears are found rarely in animals and have never been reported to intermesh and rotate functionally like mechanical gears. We now demonstrate functional gears in the ballistic jumping movements of the flightless planthopper insect Issus. The nymphs, but not adults, have a row of cuticular gear (cog) teeth around the curved medial surfaces of their two hindleg trochantera. The gear teeth on one trochanter engaged with and sequentially moved past those on the other trochanter during the preparatory cocking and the propulsive phases of jumping. Close registration between the gears ensured that both hindlegs moved at the same angular velocities to propel the body without yaw rotation. At the final molt to adulthood, this synchronization mechanism is jettisoned.

Original press releas: http://www.cam.ac.uk/research/news/functioning-mechanical-gears-seen-in-nature-for-the-first-time