We'll see. I'm getting a late start, coming in on the 5th of August, but I think that's not going to be a problem. As she said, there are no blog police enforcing this goal.
Can I keep those blog posts to less than 350 words?
No, I can't--asked and answered. What I will aim for is to stay on point, and provide valuable information, rather than just indulging my long-windedness.
You'll be the ones to let me know how well--or not--I have succeeded at that task.
The Renaissance artist Leonardo da Vinci is famous for, among other things, his sketches in which his eye for detail and his technical proficiency are immediately evident.
In the reproductive biology e-Book, Richard Bowen has a post called "Leonardo's Error", demonstrating how even an artist as meticulous as Leonardo da Vinci can make a mistake--in his case, one that continues to this day, since he's no longer in any position to correct it.
No blame, no shame: we all make errors, and if we are fortunate, then we get an opportunity to correct those errors. The most important thing is to learn from the errors we make, and use them to do better in the future.
To understand Leonardo's error in his embryological drawings, we'll first talk a little bit about the placenta, and then go back to see how and why he got that confused.
In mammals, including humans, the placenta is an organ shared by a pregnant female and the developing fetuses.
The shared blood supply between the mother and the fetuses permits food, other nutrients, and oxygen to be delivered from the mother, and it also takes waste products away from the fetuses to be disposed of.
Classification Based on Placental Shape and Contact Points
Examination of placentae from different species reveals striking differences in their shape and the area of contact between fetal and maternal tissue:
Diffuse: Almost the entire surface of the allantochorion [the membranes between the mother and fetuses] is involved in formation of the placenta. Seen in horses and pigs.
Cotyledonary: Multiple, discrete areas of attachment called cotyledons are formed by interaction of patches of allantochorion with endometrium. The fetal portions of this type of placenta are called cotyledons, the maternal contact sites (caruncles), and the cotyledon-caruncle complex a placentome. This type of placentation is observed in ruminants.
Zonary: The placenta takes the form of a complete or incomplete band of tissue surrounding the fetus. Seen in carnivores like dogs and cats, seals, bears, and elephants.
Discoid: A single placenta is formed and is discoid in shape. Seen in primates and rodents.
The discoid placenta--the kind we humans have--is one discrete organ, and looks kind of like a single disk, which is where the name comes from. You can see it in the previous drawing of the mother and child--it's drawn in a uniform red color.
By contrast, a cotyledonary placenta, like sheep and other similar animals have, looks like this:
And now, you can see Leonardo's error. He drew the human fetus like this:
Clearly, he envisioned it having a cotyledonary placenta. He confused it with the kind of placenta cows, sheep, and other similar animals have--probably because he had access to dissections of those animals, but opportunities to observe autopsies of pregnant women were relatively rare or non-existent for him.
There are, I think, 2 lessons for us here. The first is:
Consult the final authority, the human body itself.
--Stephen W. Carmichael
Even more than that, though, don't be afraid to make mistakes.
Errors happen to the best of us, even to famous artists like Leonardo da Vinci.
We can't hope to never make a mistake--they're unavoidable, simply by nature of our being human.
What we can do is to approach learning with a certain amount of humility in the face of that fact, and to hope that, when we inevitably do make errors, that we get an opportunity to correct them and to continue learning.
terrestrial nests: nests dug in holes in the ground
68C = 154.4 degrees Fahrenheit
(b) Egg collection
funnel traps: this is the basic idea of a trap where the turtle enters through a funnel, and then can't get out, but don't take this too literally as being the actual trap they used, as I couldn't find a picture of that
subcutaneous intramuscular injection: I think they just mean "intramuscular" here; "subcutaneous intramuscular" doesn't make much sense, as they're two different types of injection.
subcutaneous injections are administered just under the skin, as in
By contrast, intramuscular injections are administered into the muscle, as in this image that shows both kinds of injections (ignore the intradermal injection, as that doesn't concern us here):
oxytocin: a hormone that has many effects, from inducing labor in humans and other mammals to promoting bonding. There's way too much knowledge about oxytocin to go into here, but it's interesting that it has analogous effects (inducing labor, stimulating egg-laying) in animals that appear so different as humans and turtles
oviposition: laying eggs
clutch: all the eggs laid at the same time by one animal
developmental asynchrony = developmental "not-same-time" = development at different times from each other
Experimental treatments were designed to test whether less advanced embryos were either hatching prematurely or potentially adjusting developmental rates throughout the incubation period.
They were investigating whether the less advanced embryos sped up development to match the stage where the more advanced ones already were, or whether they kept going at their normal rate and just ran out of time at the end before finishing development.
26C: 78.8 degrees Fahrenheit
30C: 86 degrees Fahrenheit
31C: 87.8 degrees Fahrenheit
two-tailed t-tests: a statistical test to determine whether to reject the null hypothesis and consider the study's alternative hypothesis to be confirmed
VCO2: volume of carbon dioxide
(d) Metabolic and heart rates
closed system respirometry: respirometry is the measurement of metabolic rates, and here, they used carbon dioxide breathed out over time as a marker of metabolic rate. Because the system was closed, they knew no carbon dioxide was coming in from outside, so any increase in CO2 had to come from the turtles' breathing it out. Measuring that increase in CO2 over time gave them the rate at which the turtles were producing it, thus, their metabolism.
A Qubit (S500) respirometer (Kingston, ON, Canada) was used to measure carbon dioxide production
Heart rates were recorded using the Buddy digital egg monitor system (Avian Biotech, UK), which is a non-intrusive method for measuring heart rates of embryos in eggs.
Incubation period was measured as the number of days from initial egg collection until pipping. Pipping (when the eggshell is first slit) is better than hatching as an index of the end of the incubation period, because it shows less variability than hatching [28].
Another example of trying to cut down on confounds--since pipping is less variable than hatching, there is less opportunity for those variations to create confounds.
Righting trials--I think this means they flipped them, and timed how long it took the turtles to right themselves to a standing position, but don't take my word for this. I will look it up when I get to the university and can get behind the paywall to read the Colbert article, and will update at that point.
straight carapace: the carapace is the dorsal (back) shell of the turtle, composed of the spine and rib fused with dermal plates. This image shows the components of the carapace.
These notes are intended to serve as a guide to reading the article by Guzzetta et al. There is a great deal of scientific jargon in the article, and the style is telegraphic--factors which make the article less accessible to people who might otherwise like to read the research for themselves.
This post is intended to accompany a reading of that article, to demystify the jargon for a non-specialist reading audience, to expand the telegraphic style, and to make explicit the implicit knowledge contained within.
The article under study is:
Guzzetta A, Baldini S, Bancale A, Baroncelli L, Ciucci F, Ghirri P, Putignano E, Sale A, Viegi A, Berardi N, Boldrini A, Cioni G, Maffei L. Massage accelerates brain development and the maturation of visual function. Journal of Neuroscience. 2009 May 6;29(18):6042-51. PMID: 19420271Free fulltext PDF of article available here.
Abstract: Environmental enrichment (EE) was shown recently to accelerate brain development in rodents. Increased levels of maternal care, and particularly tactile stimulation through licking and grooming, may represent a key component in the early phases of EE. We hypothesized that enriching the environment in terms of body massage may thus accelerate brain development in infants. We explored the effects of body massage in preterm infants and found that massage accelerates the maturation of electroencephalographic activity and of visual function, in particular visual acuity. In massaged infants, we found higher levels of blood IGF-1. Massage accelerated the maturation of visual function also in rat pups and increased the level of IGF-1 in the cortex. Antagonizing IGF-1 action by means of systemic injections of the IGF-1 antagonist JB1 blocked the effects of massage in rat pups. These results demonstrate that massage has an influence on brain development and in particular on visual development and suggest that its effects are mediated by specific endogenous factors such as IGF-1.
The first paragraph is pretty straightforward and relatively easily readable, although there are a few points worth remarking upon.
When you read their sentence "EE has remarkable effects on adult brain function in several species", this is a good opportunity to remember that we used to think the adult brain was far less plastic than it turns out to be in reality.
Here, I am using the word "plastic" as in "plastic surgery", meaning that it lends itself to being molded or shaped or formed. The fact that the adult brain is somewhat plastic means that negative experiences in the past that influenced the brain have at least a hope of being recovered from.
Let's review how the visual system works, to ensure that we're all on the same page.
Action item (AI) 1/Raven: review of the visual system: I'll post it in this discussion, and in the human systems e-Book, when it is finished--most likely, by end of day (EOD) Monday.
"Appreciable" means empirically detectable, measurable.
AI 2/Raven: put definition of "appreciable" in the wiki.
For many of us--not all, since massage education in the United States is so variable--one of the first things we learned in anatomy and physiology class was the various levels of analysis that we could look at in an anatomical structure and its physiological function. Even so, those we learned did not represent all possible levels, but just the ones most useful at the beginning, such as the gross anatomical level or the systems level.
Question 1: Can you give an example of a structure and its function at the behavioral level, at the electrophysiological level, and at the molecular level?
There is a lot of technical language in the 2nd paragraph, but it really refers to only a few foundational concepts. Once you know how, for example, a BDNF receptor works, you will understand how an NMDA receptor works when you come across it, because it's the same general idea--the specific molecule involved is the only change.
So don't let a skim of this paragraph discourage you--it's not nearly as hard as it looks at first glance.
Question 2: What seems to be the cause-and-effect connection between EE and improved function and behavior in pups?
Question 3: Can you think of an analogy in human behavior? Remember, we are not claiming that we know that this is true, but that it could possibly serve as a testable hypothesis for further study.
"[L]icking and grooming provided by the mother has been shown to influence [here, positive influence is implied]:
Although there remains a lot that we don't know about what the hippocampus does, it is fairly well-established that it plays a major role both in memory and in spatial coding (mental representations of the spatial relations between objects). [1]
Guzzetta also states that the level of licking and grooming provided by the mother affects molecules crucial for plasticity, meaning the brain's ability to be shaped or formed in new ways and to form new connections, rather than being frozen and relatively unable to change.
In this context of the brain, this refers to proteins and other molecules that promote the growth and development of brain cells (a process called neurogenesis), since the dynamics governing that growth and development is where plasticity comes from.
BDNF, short for Brain-Derived Neurotrophic Factor, is:
is a protein expressed by the BDNF gene;
is a growth factor;
is involved in neurogenesis;
is suppressed in cases of depression;
increased by the neurotransmitter glutamate, exercise, caloric restriction, intellectual stimulation
active and present in high concentrations in brain areas vital to learning, memory, and higher thinking, such as the hippocampus and cortex. [2]
NMDA, short for N-Methyl-D-aspartic acid, is a molecule that mimics the action of the neurotransmitter glutamate, so it can stand in for glutamate when investigating the neurotransmitter's action under certain circumstances.
novelty reaction
exploratory behavior
Exploration is the act of making the unknown known and is a fundamental adaptive behavior across many species. A related adaptive behavior is novelty seeking, defined as a proclivity to approach unfamiliar situations. Abnormal exploratory behavior and novelty seeking are characteristic of many neuropsychiatric conditions, including excessive activity observed in bipolar mania, increased novelty seeking in substance use disorders, and prominent inactivity and withdrawal as observed in schizophrenia. For several decades, numerous animal paradigms of neuropsychiatric illness have assessed the multiple dimensions of exploratory behavior and novelty seeking. These models have been useful in elucidating underlying neurobiological mechanisms and testing novel psychotropic treatments. [3]
spatial learning and memory
level of glucocorticosteroid receptors in the hippocampus
Glucocorticoids are steroid hormones that play a role in reducing inflammation and in normal brain development. [4]
feedback control on hypothalamus-pituitary-adrenal axis
The hypothalamic–pituitary–adrenal (HPA) axis is a major system of hormonal control over many functions in the body. Much like a thermostat uses surrounding heat to tell if it needs to continue heating or to turn off the heat, the HPA axis checks blood levels of circulating hormones to determine whether to stimulate or stop stimulating hormone production in the glands in the system.
spine density and synaptic plasticity in hippocampus
This refers to the structure and plasticity of neurons in the hippocampus.
negative effects produced by maternal separation/deprivation or prenatal stress on:
pup growth
growth hormone (GH) secretion
Growth hormone, secreted by the anterior pituitary gland, plays a major role in structure growth and regulation of other hormonal systems in the body, such as the production of IGF-1.
HPA axis
BDNF expression
synaptophysin expression
Synaptophysin is a protein expressed by the SYP gene. The exact function of the protein is unknown...Recent research has shown, however, that elimination of synaptophysin in mice creates behavioral changes such as increased exploratory behavior, impaired object novelty recognition, and reduced spatial learning. [5]
"rescued": here it means "mitigated", or "alleviated"
"Working in preterm infants, Schanberg and Field (1987) found evidence that massage promoted a faster weight gain and a lower level of cortisol in massaged infants."
Question 4: What's wrong with this sentence?
Paragraph 3 is relatively straightforward and easy to understand.
Paragraph 4
Visual evoked potentials (VEPs) are measurements of electrical activity in the nervous system after some source of visual stimulation has occurred. For example, an investigator might use VEPs to trace the activity in the brain to see what happens when the subject is watching a flashing light.
Visual acuity is the sharpness or clearness of someone's vision--how clearly they can see.
Source: http://upload.wikimedia.org/wikipedia/commons/9/9f/Snellen_chart.svg accessed 4 December 2011
Electroencephalography (EEG) is the measurement of the brain's electrical activity
In paragraph 5, Guzzetta states that "IGF-1 mediates EE effects on visual cortical development". To "mediate" means to be in the middle of other things. Let's say the independent variable (roughly, the "cause") in the following figure is EE, and the dependent variable (roughly, the "effect") is visual cortical development.
Path C shows a connection where EE directly causes visual cortical effects. But here, Guzzetta is saying that that is not the case--instead, EE has an effect on IGF-1 (path A), and IGF-1 then has an effect on visual cortical effects (path B). IGF-1, then, mediates (is a mediator variable between) EE effects and visual cortical development.
So now that we've established the role that Guzzetta's team proposes it plays in mediating the effects of EE into visual cortex development, let's talk about what IGF-1 is.
IGF-1:
is a protein molecule, encoded by the IGF1 gene, that functions as a hormone;
is named Insulin-like Growth Factor 1:
"Insulin-like" because of its structural similarity to insulin;
"Growth Factor" because of its lifelong anabolic role;
"1" because it is a member of a family of structurally-related proteins, such as IGF-2;
is produced mostly by the liver;
is a primary mediator of Growth Hormone (GH);
appears to play a major role in biological aging and cancer, as well as in normal growth. [6]
the anterior pituitary in the brain produces GH, and releases it into the blood;
GH goes to the liver, and stimulates it to produce IGF-1, and release it into the blood;
IGF-1 causes growth in many different kinds of cells in the body, including the ones we're interested in here: the visual cortical cells in the occipital lobe.
Guzzetta also states that EE increases the number of IGF-1-positive neurons in the visual cortex; this is an example of neurogenesis.
They describe how increasing IGF-1 in the visual cortex of non-EE rats by means of osmotic minipumps mimics EE effects, accelerating visual acuity development.
An osmotic minipump is a tiny implantable device that delivers IGF-1, which the rat's cells then take up by osmosis.
AI 3/Raven: finish demonstration of diffusion, use that to lead into osmosis
The visual cortex is the part of the brain that processes information delivered from the eyes. This is the brain of a person whose hair, skin, and skull have been digitally removed from the image.
The person is facing away from you, so you are looking at the back of their head: the occipital lobe.
A funny thing is that--although the eyes are in the front of the head, the information they deliver has to travel all the way to the back to be processed, and then is projected all the way back up front to the eyes again, which gives the perception that vision is in our eyes.
The name "visual cortex" tells us that it's in the cortex, or outer layer of the cerebrum--the darker purple in this picture of a slice of brain tissue; the gray matter of the brain, as opposed to the inner layer of white matter.
Guzzetta observes that blocking IGF-1 action in the visual cortex of EE rats by means of the IGF-1 receptor antagonist JB1 blocks EE action on visual acuity development. JB-I blocks IGF-I signaling; in the following discussion of antagonists, we'll discuss in more detail how it does so.
They also observe that massage led to increased levels of blood IGF-1 and IGF1BP3 in human infants. IGFBP-3 is a carrier or a binding protein for IGF-1, preventing the kidney from quickly clearing it from the blood, as it normally would. [6]
Guzzetta states that massage led to increased number of IGF-1 positive neurons in the cortex in rat pups.
Question 5: Why didn't they test this in human infants?
Guzzetta also observes that antagonizing IGF-1 action blocked the effects of massage in rat pups. You can think of an antagonist at a molecular level as being both similar to and different from an antagonist at the muscular level.
Like a muscular antagonist, a molecular antagonist works against, or opposes, another molecule. But the way in which it opposes that other molecule is not like how an antagonist muscle works.
A molecular antagonist is similar enough to the other molecule that it can slip into the "lock-and-key" receptor, and block it off, so that when the other molecule arrives, it cannot find a receptor to take it up.
So Guzzetta is saying that they hypothesize that the effects of massage are mediated by IGF-1, and the fact that an IGF-1 antagonist blocked the effects of massage reinforces the hypothesis that massage affects the visual cortical neurons in a way that is mediated by IGF-1.
Question 6: Why didn't they test this in human infants?
Question 7: What is the purpose of Guzzetta's study?
Imagine you're explaining it to someone you just met at a party, or on the bus, not in the lab or clinic--use that level of language, rather than Guzzetta's jargon.
Question 8: What did they say about their results in this paragraph?
[3] Minassian A, Henry BL, Young JW, Masten V, Geyer MA, Perry W. Repeated assessment of exploration and novelty seeking in the human behavioral pattern monitor in bipolar disorder patients and healthy individuals. PLoS One. 2011;6(8):e24185. PMID: 21912623
Anatomy is a foundational discipline in massage therapy, and the embryology/developmental biology of those structures is key to understanding anatomy;
You care about the natural world, the environment, and the animals in it, and you want to better understand the threats they face, so that you can take more effective action to protect them from those threats;
You want to better understand science in order to be a well-informed citizen, to participate in policy debates and decisions from a position of knowledge and effectiveness.
These are my notes on the Introduction to the following article:
Embryonic communication in the nest: metabolic responses of reptilian embryos to developmental rates of siblings
Jessica K. McGlashan, Ricky-John Spencer and Julie M. Old, Water and Wildlife Ecology Group, Native and Pest Animal Unit, School of Natural Sciences, University of Western Sydney, Locked Bag 1797, Penrith South DC, New South Wales 1797, Australia. Proc Biol Sci. 2011 Nov 30. Free fulltext PDF of article available here.
Incubation temperature affects developmental rates and defines many phenotypes and fitness characteristics of reptilian embryos. In turtles, eggs are deposited in layers within the nest, such that thermal gradients create independent developmental conditions for each egg. Despite differences in developmental rate, several studies have revealed unexpected synchronicity in hatching, however, the mechanisms through which synchrony are achieved may be different between species. Here, we examine the phenomenon of synchronous hatching in turtles by assessing proximate mechanisms in an Australian freshwater turtle (Emydura macquarii). We tested whether embryos hatch prematurely or developmentally compensate in response to more advanced embryos in a clutch. We established developmental asynchrony within a clutch of turtle eggs and assessed both metabolic and heart rates throughout incubation in constant and fluctuating temperatures. Turtles appeared to hatch at similar developmental stages, with less-developed embryos in experimental groups responding to the presence of more developed eggs in a clutch by increasing both metabolic and heart rates. Early hatching did not appear to reduce neuromuscular ability at hatching. These results support developmental adjustment mechanisms of the ‘catch-up hypothesis’ for synchronous hatching in E. macquarii and implies some level of embryo–embryo communication. The group environment of a nest strongly supports the development of adaptive communication mechanisms between siblings and the evolution of environmentally cued hatching.
→ what makes young in same clutch (set of eggs) vary in timing? Order of ovulation, thermal micro-environments of eggs can have effect
→ despite these differences, many egg-laying animals (including invertebrates, fishes, amphibians, crocodilians, snakes, turtles, and birds) are able to synchronize hatching
→ Freshwater turtles: give us a chance to see how this process actually works
→ Eggs ovulated simultaneously, then fertilized, then begin dividing (1 cell → 2, 2 → 4, 4 → 8, ...). At first, the divisions are exactly like each other (“undifferentiated”), but when enough cells have built up into a mass, it begins to differentiate (specialize) into layers (3 in animals like us, and turtles are not that different from us, relatively speaking). The stage at which 3 layers (ectoderm, mesoderm, endoderm) are present, but have not yet begun to form distinct organs, is called “gastrulation”, and the cells themselves form the gastrula.
→ At this point, mama turtle hits the pause button (not literally; the process occurs all by itself--she doesn't have to actively do it), and the embryos are halted at gastrulation until they are safely in the nest, and can pick up developing where they left off
→ mama comes out of the water and digs hole in ground to build nest. eggs are deposited in the nest in layers, and even though the nest is shallow, there is still room for detectable environmental variation in it. For this reason, we expect the eggs to respond to that temperature variation, and hatch at different speeds in different layers from top to bottom.
→ eggs in the top layers can experience temperatures up to 68C higher than eggs in the bottom layers. To know what that means, you can use the exact formula for converting Celsius/Centigrade temperatures to Fahrenheit, but since we don't need to be that exact just to discuss it, we can use the quick and dirty conversion of doubling the C temperature, and then adding 30. So if the temperature can be up to 68C higher in the upper layers than in the lower layers, then that means it can be up to (68 times 2 = 136 degrees Fahrenheit + 30 = ) 166 degrees Fahrenheit hotter in the upper layers. That's quite a big difference, so we expect—as previously discussed—that the eggs exposed to those higher temperatures will hatch quite a bit faster than those in the lower layers. Is what we predict actually what happens in the natural world?
→ Surprisingly, no, it isn't. The temperature difference does not produce the difference in hatching times that we would expect. Both in Australian and North American freshwater turtles, we observe less-developed siblings “catch up” to the more-developed ones in the upper layers. In some cases, they just hatch earlier; in other cases, they actually increase their rates of development in response to biochemical cues from their siblings, regardless of their own actual temperature.
→ What would explain this difference between what we predict and what actually happens? Ultimate (“big-picture”) explanation: avoiding predators is a selection pressure (a strong influence) that drives the evolution of synchronous hatching. This is a mindliess process; no one actually “decides” to do something differently to avoid predators. Instead, in a big enough population of turtles, you'll have some that randomly happen to hatch at the same rates, and others that hatch at different rates. If hatching at the same rate gives those turtles a survival advantage compared to the other turtles, then more of them will survive. Surviving longer means they have more chance to pass that trait to their offspring, which means more of those offspring will survive to reproduce, and the cycle continues.
→ If avoiding predators is a possible explanation of what we observe, then what might be the actual mechanism of that process?
→ Ever seen a bicycle race where cyclists “draft” in the wake of other cyclists to gain a slight advantage of speed without having to spend as much energy on it, or been in a crowd trying to push its way into a concert? There is an analogous energy advantage to being pushed along with the group as everyone leaves the nest at once, rather than having to spend all the energy to dig and pull yourself out individually from the bottom layer.
–> If a predator is waiting by the nest, one turtle coming out all by itself is a nice snack. A large group of turtles, on the other hand, may “swamp” and confuse the predator. Even if it doesn't, and the predator does get a turtle or ten, then in a group, any given individual's chances of escaping the predator are better in a crowd than if the individual is totally alone in coming out of the nest.
→ These are potential scenarios where group simultaneous hatching and emergence can reduce the amount of energy an individual spends, and increase an individual's chances of survival. What are the costs required to produce these advantages?
→ remember, the predator scenario was the “ultimate” or big-picture cause. Proximate, or “near-by” or “immediate” causes would include detecting sibling hatching or developmental cues, and responding to those cues by changing your own developmental rate (not consciously, but biochemically)
→ perhaps the less-developed siblings have poorer motor sklls, so they are at more risk from predators than the more-developed turtles are
→ perhaps being less-developed makes those turtles more likely to die from natural causes
→ what are the possible ways to link hatching times among siblings? The slower ones can speed up, or the faster ones can slow down
→ Hatching out of the eggs can be tightly linked to emergence from the nest, or it can be not tightly linked—the young turtles hang out in the nest for a while before emerging and heading to the water
→ One species of freshwater turtle, Chrysemys picta: the slower ones hatch prematurely rather than the faster ones slowing down, but hatching and emergence are not closely linked. This gives the slower ones a little time after hatching to continue developing before finally emerging.
"Hi! I'm what's called a 'painted turtle', Chrysemys picta. We hang around the nest for a little while after hatching and before emerging into the world."
→ A different species, Emydura macquarii, emerges very soon after hatching—no hanging around in the nest time for continued development in these turtles. What this means is that the slower ones, in catching up, kind of skimp on the secondary period of development. The primary period (where organs and tissues develop) is pretty much on track, but the speeding up to catch up to their warmer/faster siblings takes a toll during the secondary period (where the neuromuscular system matures).
"Hi! We're Emydura macquarii, the Murray River Turtle. We pretty much hit the road once we hatch."
→ Figure 1: metabolic profile for freshwater turtle eggs during incubation, based on E. macquarii eggs.
→ The plotted lines (black solid, gray solid, black dotted, and gray dashed) begin when incubation begins—remember, we said previously that the embryo is paused at the gastrula stage until mom digs a nest and lays the eggs in it.
→ 0 on the horizontal line (x-axis) represents the moment she lays them in the nest and incubation starts/the embryo resumes developing. They end when hatching occurs, about 52-67 days later for this species.
→ 0 on the vertical line (y-axis) represents 0% of the peak (top) metabolic rate—the gastrula is not carrying out metabolic processes. Once incubation begins, metabolism also starts, and increases continuously until it reaches peak metabolic rate. Then something interesting happens—notice the lines dropping off when they come into contact with the gray bars. We'll talk about what that is, and what it means, when we talk about those bars.
Source: Figure 1 from article
→ The solid black line shows the process that normally-developing eggs follow. This tells us the natural baseline against which we are comparing all the other eggs that have had interventions (some kind of stimulus to promote development).
→ The solid gray line shows eggs that were incubated separately at warmer temperatures for the first week of development before being reunited with the normally-developing eggs. So the line is the same shape, because it follows the same process—it is just shifted left (lower number of days of incubation) because the temperature caused everything to happen faster. So at 5 days, the gray line is already as high (increased percentage of peak metabolic rate) as the black line is normally at 20 days. This tells us about the speed-up effect caused by temperature alone. This group of eggs is called the “stimulus eggs”.
→ At about 12 days of incubation, the gray dashed line—which was previously invisible, because it was exactly following the solid black line--breaks away from the black line and starts showing a faster increase in its percentage of peak metabolic rate than it had been showing to that point. That's because it had previously been permitted to develop normally, and then, in early development, they had been stimulated to develop faster. Notice that the gray dashed line eventually joined the gray solid line—it caught up to the “stimulus eggs”, even though it got its own stimulation about 12 days later.
→ At about 35 days of incubation, much later in development, the eggs represented by the black dotted line also received a stimulus. Notice how fast they shot up to also catch up to the “stimulus eggs”. The line is quite steep, because they had a lot of ground to make up before hitting the peak metabolic rate in such a short time, but they succeeded at doing so.
→ What this tells us is that all the stimulated eggs—whether from the beginning, or from 10 days into incubation, or from 35 days into incubation—reached peak metabolic rate at just about the same time. So the eggs that were stimulated later all managed to catch up to the eggs that were stimulated at the very beginning.
→ The plain white area of the graph before the bars where the plotted lines hit peak metabolic rate represent the primary developmental period—the period where the organs and tissues are formed in the embryos.
→ The gray bars represent the secondary developmental period, where neuromuscular development takes place. As you would expect, the light gray bar—which represents the secondary developmental period in the stimulated eggs—is shifted left, or occurs about a week before, the dark gray bar, which represents the secondary developmental period in normally-developing eggs.
→ Although the light gray bar is time-shifted from the dark gray bar, they each show a similar interaction with their corresponding plotted line. The line hits about 100% peak metabolic rate just as the secondary developmental period starts, and then drops off sharply, going back to about 75% of peak metabolic rate. The article explains what is happening: “Respiration rates in reptiles and precocial birds generally drop by up to 25 per cent before hatching occurs, but hatching can occur at any time after peak metabolism. The fall in metabolism prior to hatching in some species is associated with the secondary development period, which is variable in length.”
→ “Reptiles” here refers to turtles, which seem to many people as though they ought to be amphibians, but they're not. They're really reptiles, based on evolutionary heritage, who enjoy an amphibian (two-life) lifestyle, in the water and out of it.
→ If you've ever heard a child referred to as “precocious”, then you've already got a mnemonic (memory aid) for remembering the difference between precocial species and altricial species. A precocious child is one who is able to carry out activities more advanced than you would expect someone at the child's developmental stage to do—maybe he read early, or she's a math whiz, or they' were able to program computers before even starting school. Similarly, precocial birds are birds whose young hatch at a relatively advanced and independent developmental stage, compared with altricial birds, whose young hatch helpless. Imagine a baby chick, pecking its way out of the egg, and looking about itself with open eyes before taking its first—if hesitating—steps. That's a precocial bird. Now visualize a songbird, whose babies come out of the egg with their eyes closed, and require a great deal of parental care before they develop to a stage where they can begin to leave the nest. That's an example of an altricial bird.
→ So like in precocial birds, the (reptilian) turtles hit peak metabolic rate, and then the secondary developmental stage starts, and their peak metabolic rate drops until they hatch. That's what the upward-sloping lines suddenly beginning to slope downwards means.
→ Once the lines begin to slope downward (the peak metabolic rate falls), then the eggs are in the secondary stage of development.
→ Bonus question here: what is cause and what is effect? Does the drop in peak metabolic rate cause the secondary developmental stage to start, or does the onset of the secondary developmental stage cause the peak metabolic rate to drop? Or are there any other possibilities? What does the graph tell us about cause and effect?
→ You see the two vertical arrows, one at the right end (final day) of each secondary developmental period. Those arrows indicate the normal hatching times for each group of eggs. These guys pretty much hatch immediately when the secondary developmental period is completed.
–> The horizontal dashed arrow in the secondary developmental period of the normally-developing eggs indicates that this is the only place left at this point in the process where the normal eggs can catch up to the “stimulus eggs”. The other eggs that started out normal, but were then stimulated, had more time to make up ground, but this is, literally, their last chance to get caught up. The only way to catch up is to shorten the time spent on neuromuscular development. And that skimping can have short- and long-term costs, and because they did not spend the full time in that stage, they may be at more risk not to survive later on when they leave the nest. But there is no other way to make up the time difference.
–> This study is intended to test the two competing proximate (“immediate”) mechanisms of the catch-up hypothesis, underlying simultaneous or early hatching in freshwater turtles. They will look at how these mechanisms can be linked to environmental temperature changes.
→ They found a reference to earlier work by Booth, where Booth's team tried transferring freshwater turtle eggs among lower- and higher-temperature environments, but failed to show any linked developmental catching up. They think that perhaps Booth missed subtle changes in temperatures during the day that could have large effects. To avoid falling into this trap that they perceive might have led Booth astray, they will evaluate mechanisms for their hypothesis both in environments with constant temperatures, and in environments where temperatures fluctuate.
This is a very nice visualization of embryological developmental processes. Alexander Tsiaras is a scientific artist and programmer who creates anatomical visualizations, based on data from CAT and MRI scans and extended with computer graphics techniques. He has taken these sources and created a lovely visualization from fertilization to birth.
From his choice of words on several occasions, he appears to be an Intelligent Design creationist. That's no reason not to enjoy and appreciate his visualizations, of course. It does mean, however, that you should take his accompanying explanations of biological processes as being too complex for mathematics or beyond human understanding with a massive grain of salt, as those claims are statements of unique religious belief rather than of universal scientific fact.
Points of interest in the talk and video
The scanning technology that these images are based on appear to be all from micro MRI (magnetic resonance imaging), if I understand him correctly. MRI, unlike CAT scans using ionizing radiation (X-rays), uses magnetic fields, and is considered non-invasive and harmless.
Later in the video, he mentions that children's brains will be scanned every six months to track their development. MRI is considered safe enough that this study got institutional approval; probably a study that exposed children to X-rays that often through CAT scans would not get that same approval. It's unclear whether MRI has no effect at all on the brain and other parts of the body--after all, strong magnetic fields are used for treating depression, OCD, and cognitive changes in Alzheimers disease--but the effect is considered at present to be minimal.
When he says that at 12 weeks, the embryo has an "indifferent penis" and that it is yet to be determined whether the fetus is a girl or a boy, he means from the standpoint of the outside observer. The fetus, of course, has a genotype of XX or XY ever since fertilization, and--assuming that all goes right--that genotype determines whether the indifferent penis will develop into a penis or a clitoris.
He depicts the baby rotating during delivery, although you should take the baby's position as art, not as literal scientific fact. Naturally, the same is true for the baby swimming away, which is also artistic interpretation rather than actual data.
The trophoblast is the outer layer of the blastocyst, both of which are structures in stages of the dividing fertilized egg. The blastocyst contains the embryoblast, a group of cells that will become the embryo. The trophoblast nourishes the blastocyst, and will eventually form part of the placenta.
At 6:39, he refers to the "trilinear fetus". He misspeaks here; he actually means "trilaminar embryo", or an embryo in the stage where it is made up of 3 layers of embryonic tissues, all of which have different cell fates in the process of development.
The three germ layers are endoderm ( ενδό/endo: "inside" + δέρμα/derma: "skin" ), mesoderm ( μέσος/mesos: "middle" + δέρμα/derma: "skin" ), and ectoderm ( ἐκτός/ektos: "outside" + δέρμα/derma: "skin" ), all three of which are visible in this slice of tissue from a teratoma, or tumor of developmental tissue.
These layers, and the structures that come out of them, are the referent, or empirical physical reality, behind some of the most lively debates and knowledge discovery in massage anatomy and physiology right now.
Do trigger points exist in the muscle, as the mesodermists assert, or in the nervous system, as the ectodermists claim?
(UPDATE, 11:53 AM PT: After discussing it with Seth Will over on the POEM Facebook page about this post (http://tinyurl.com/8xs8ku2), I'm convinced my previous sentence is overly simplistic. Since I don't want to start the embryology discussion, and later trigger point discussions, out on the wrong track, I'll change it to this, which is more accurate:)
They inform, for example, the theoretical basis behind the real-life observation of trigger points. This theoretical basis, currently under development and refinement, continues to underlie our understanding and effectiveness in addressing the needs of our clients.
What do we need to know and to do in order to figure these issues out?
What is dermoneuromodulation?
The answers to many of the most fascinating questions about the body lie in the stages that Tsiaras depicts in this video.
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