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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.

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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
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Home | Pregnancy Timeline | News Alerts |News Archive Oct 23, 2014

The Jonah crab (Cancer borealis) and other invertebrates are useful in neuroscience research
because their neurons are similar enough to our own that research results can be “scaled up”
to apply to higher organisms like ourselves.

 







CDC Growth Standards 0 to 2 Years of Age

 

 

 

Neurons “fine tune” themselves at gene level

A new study provides the first biological evidence that neurons continually “tune” their molecular machinery to regulate the flow of ions and the electrical charge neurons carry.

Neurons are electrically charged cells that interpret and transmit information by electro-chemical signals. The amount of a neuron’s electrical charge is determined by the flow of charged ions in and out of its' cell wall through ion channel pores. When the cell wall pores open, ions rush in. When those pores close the neuron is said to be "charged".

David Schulz is associate professor of Biological Sciences at the University of Missouri-Columbia, in Columbia, Missouri, USA. He led the research — which appears on the August cover of Current Biology. His research found that individual neurons maintain levels of messenger RNA (mRNA are  the molecules that carry instructions from genes to the protein-making machinery of the cell) to ensure a consistent ratio of open and closed ion channels.


“We used to think a neuron’s electrical output was determined by a fixed number of ion channels in the cell wall. Now, we realize the number of ion channels can be totally different as long as it balances out.”

David Schulz PhD, associate professor, division of biological sciences, College of Arts and Science, in the Interdisciplinary Neuroscience Program at Missouri University.


Therefore, the relative ratio of ion channels opening and closing and not the underlying number of channels, is what is important in generating each neuron’s spark. Thus, the activity of a neuron with 20 open channels and 30 closed channels is functionally the same as a neuron with 80 open channels and 120 closed channels.

Recent computer models had predicted that mRNA levels could directly regulate, or correlate, ion passage in and out of a neuron, but this had never been demonstrated in living neurons. Schulz tested this hypothesis on the stomatogastric ganglion (the center of a network of nerves and muscles that helps the crab process food) in the Jonah crab or Cancer borealis. Crabs and other invertebrates are useful in neuroscience research because their neurons are similar enough to our own that the research can be “scaled up” to apply to higher organisms.

Using a mix of molecular and electrophysiological approaches, Schulz and colleagues established ion channel correlations in six different types of nerve cells — each with specific outputs. To determine how mRNA maintains a balance of ion transfer through the cell wall, researchers decoupled the nerve cell’s electrical activity in every possible type of neuron and its' configuration.

“When we finally got through whittling down neural activity, we found the molecular level at which channels trigger control over ratios. There is a constant detection process of "in-out" channel activity which is signalled back to whatever controls the mRNA level keepping ion activity on a balanced track.” Schulz believes nerve cells are constantly fine “tuning” themselves to maintain this consistent electrical output.

Schulz hopes these results might someday be useful in developing therapeutics for neurological disorders.


“Genetic mutations often found in neurological disorders create imbalances in the "in and out" flow of electrical current through cells. The variability of these imbalances, even between multiple cells of the same kind within the brain, is one of the major problems scientists face when trying to design therapeutics for disorders like epilepsy. 

"Because seizures in individuals can be initiated by an imbalance in regulation of the ionic charge of neurons, getting to the root of how neurons stabilize ion exchange is essential to future treatment.”


David Schulz PhD


Highlights
•Channel mRNAs are present in distinct cell-specific relationships
•Correlations among channel mRNAs are dynamically maintained
•Disrupted activity results in the loss of all mRNA correlations within 8 hr
•Artificially maintained activity rescues the loss of correlated mRNAs

Summary
Neurons generate cell-specific outputs via interactions of conductances carried by ion channel proteins that are homeostatically regulated to maintain key quantitative relationships among subsets of conductances [ 1–3 ]. Given the challenges of both normal channel protein turnover and short-term plasticity, how is the balance of membrane conductances maintained over long-term timescales to ensure stable electrophysiological phenotype? One possible mechanism is to dynamically regulate production of channel protein via feedback that constrains relationships at the channel mRNA level. Recent modeling work has postulated that such mRNA relationships could emerge as a result of activity-dependent homeostatic tuning rules that ensure an appropriate ratio of mRNA for key ion channels is maintained to preserve robust cellular output [ 4, 5 ]. Yet, this has never been demonstrated in biological neurons. In this study, we quantified multiple ion channel mRNAs from single identified motor neurons of the stomatogastric ganglion to determine whether correlations among channel mRNAs are actively maintained, and, if so, by what form of feedback. In these neurons, we identified correlations among mRNAs for voltage-gated calcium and potassium channels. By performing experiments that decoupled activity, synaptic connectivity, and neuromodulatory state, we determined that correlated channel mRNAs are maintained by an activity-dependent process. This is the first study to demonstrate that distinct relationships across channel mRNAs are dynamically maintained in an activity-dependent manner. This feedback from cellular activity to coordinated transcriptome-level interactions represents a novel aspect of regulation of neuronal output with implications for long-term stability of neuron function.

Coauthors of the study include former graduate student Simone Temporal, Ph.D. 13, and current graduate student Kawasi Lett.
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