Happy Atheist Forum

Recent Posts

Pages: [1] 2 3 ... 10
1
Politics / Re: Dominionists in the United States
« Last post by No one on Today at 03:56:42 AM »
President Pot has just met Senator Kettle.
2
Science / Re: They Don't Swim the Way We Thought
« Last post by Dark Lightning on Today at 12:41:26 AM »
Starts with a screw, ends with a screw. (Sorry, couldn't resist).

 >:( Damn! Ninja'd!  ;D
3
Science / Re: They Don't Swim the Way We Thought
« Last post by Ecurb Noselrub on August 06, 2020, 11:03:52 PM »
Starts with a screw, ends with a screw. (Sorry, couldn't resist).
4
Politics / Re: Dominionists in the United States
« Last post by Recusant on August 06, 2020, 11:02:10 PM »
Out there rallying the Christian soldiers. As if anybody who'd take this seriously would be voting for somebody else, or would fail to vote.

5
Science / Re: They Don't Swim the Way We Thought
« Last post by Randy on August 06, 2020, 06:18:36 PM »
Interesting. Whenever I see videos about this subject I'll picture them swimming in a corkscrew manner,
6
Thanks! I really like it. I may take some leisure out there now that the photon flux is only about 30% of what it used to be.  ;D I need to get the coffee tables and chairs assembled and finished. I'll be using boiled linseed oil.
7
Quite a striking effect.
8
Politics / Re: Political picture dump
« Last post by Recusant on August 06, 2020, 07:26:32 AM »
9
Science / They Don't Swim the Way We Thought
« Last post by Recusant on August 06, 2020, 04:40:16 AM »
Spermatozoa, that is. The article tells a decent story even if there are some imprecise statements, so if you'd prefer to learn about this there, skip the--
Spoiler: ShowHide
It was thought that they did a straight-forward wiggle, but it turns out they have a sort of sideways wiggle that is compensated for by the whole cell rotating on an axis which "balances out" the one-sided wiggle, so that they essentially corkscrew through the fluid, rather than wiggle like an eel.


"Sperm fooled scientists for 350 years – they spin not swim" | The Conversation

Quote
Sperm is critical for the fertilisation of almost every living organism on our planet, including humans. To reproduce, human sperm have to swim a distance equivalent to climbing Mount Everest to find the egg. They complete this epic journey simply by wiggling their tail, moving fluid to swim forwards. Though over 50 million sperm will fail to reach the egg – the equivalent to more than six times the entire population of London or New York – it only takes one single sperm in order to fertilise an egg that will eventually become a human being.

Sperm was first discovered in 1677 – but it took roughly 200 years before scientists agreed on how humans are actually formed. The “preformationists” believed that each spermatozoa contained a tiny, miniaturised human – the homunculus. They believed that the egg simply provided a place for the sperm to grow.

On the other hand, the “epigenesists” argued that both males and females contributed to form a new being, and discoveries in the 1700s showed more evidence for this theory. Though scientists now better understand the role that sperm plays in reproduction, our latest research has discovered that sperm have actually been fooling scientists this whole time.

[Snipped more science history.]

Using state-of-the-art 3D microscopy technology, our team of researchers from the UK and Mexico, were able to mathematically reconstruct the rapid movement of the sperm tail in 3D. Not only does sperm’s size make them difficult to study – its tail only measures half a hair’s breadth – they’re also fast.

Their tail’s whip-like movement is capable of beating over than 20 swimming-strokes in less than one second. We needed a super-fast camera capable of recording over 55,000 pictures in one second mounted in a fast oscillating stage to move the sample up and down at an incredibly high rate – effectively scanning the sperm tail while swimming freely in 3D.

What we found surprised us. We discovered that the sperm tail is in fact wonky and only wiggles on one side. While this should mean the sperm’s one-sided stroke would have it swimming in circles, sperm have found a clever way to adapt and swim forwards: they roll as they swim, much like the way otters corkscrew through water. In this way, the wonky one-sided stroke evens out as sperm rolls allowing it to move forwards.

The sperm’s rapid and highly synchronised spinning causes an illusion when seen from above with 2D microscopes - the tail appears to have a side-to-side movement. However, this discovery shows that sperm have developed a swimming technique to compensate for their lop-sidedness. In doing so they have also ingeniously solved a mathematical puzzle: by creating symmetry out of asymmetry.

The sperm body spins at the same time that the tail rotates around the swimming direction. Sperm “drills” into the fluid like a spinning top by rotating around itself whilst its tilted axis rotates around the centre. This is known in physics as precession, much like the precession of the equinoxes in our planet.


[Continues . . .]

It appears the paper is open access.

"Human sperm uses asymmetric and anisotropic flagellar controls to regulate swimming symmetry and cell steering" | Science Advances

Quote
Abstract:

Flagellar beating drives sperm through the female reproductive tract and is vital for reproduction. Flagellar waves are generated by thousands of asymmetric molecular components; yet, paradoxically, forward swimming arises via symmetric side-to-side flagellar movement. This led to the preponderance of symmetric flagellar control hypotheses. However, molecular asymmetries must still dictate the flagellum and be manifested in the beat. Here, we reconcile molecular and microscopic observations, reconnecting structure to function, by showing that human sperm uses asymmetric and anisotropic controls to swim. High-speed three-dimensional (3D) microscopy revealed two coactive transversal controls: An asymmetric traveling wave creates a one-sided stroke, and a pulsating standing wave rotates the sperm to move equally on all sides. Symmetry is thus achieved through asymmetry, creating the optical illusion of bilateral symmetry in 2D microscopy. This shows that the sperm flagellum is asymmetrically controlled and anisotropically regularized by fast-signal transduction. This enables the sperm to swim forward.
10
Science / Re: All things brain...
« Last post by Recusant on August 05, 2020, 09:07:40 PM »
A new MRI study indicates that the surface area of the human cerebellum is greater than had previously been thought.


"'Little brain' or cerebellum not so little after all" | ScienceDaily

Quote

Cerebellum highlighted in illustration of brain. Image credit: © decade3d / stock.adobe.com



When we say someone has a quick mind, it may be in part thanks to our expanded cerebellum that distinguishes human brains from those of macaque monkeys, for example.

Sometimes referred to by its Latin translation as the '"little brain"', the cerebellum is located close to the brainstem and sits under the cortex in the hindbrain. New research at San Diego State University, however, calls the "little" terminology into question.

The cerebellum plays a versatile role, contributing to our five senses as well as pain, movements, thought, and emotion.

It's essentially a flat sheet with the thickness of a crepe, crinkled into hundreds of folds to make it fit into a compact volume about one-eighth the volume of the cerebral cortex. For this reason, the surface area of the cerebellum was thought to be considerably smaller than that of the cerebral cortex.

By using an ultra-high-field 9.4 Tesla MRI machine to scan the brain and custom software to process the resulting images, an SDSU neuroimaging expert discovered the tightly packed folds actually contain a surface area equal to 80% of the cerebral cortex's surface area. In comparison, the macaque's cerebellum is about 30% the size of its cortex.

"The fact that it has such a large surface area speaks to the evolution of distinctively human behaviors and cognition," said Martin Sereno, psychology professor, cognitive neuroscientist and director of the SDSU MRI Imaging Center. "It has expanded so much that the folding patterns are very complex."

[Continues . . .]

The paper is open access:

"The human cerebellum has almost 80% of the surface area of the neocortex" | Proceedings of the National Academy of Sciences

Quote
Abstract:

The surface of the human cerebellar cortex is much more tightly folded than the cerebral cortex. It was computationally reconstructed for the first time to the level of all individual folia from multicontrast high-resolution postmortem MRI scans. Its total shrinkage-corrected surface area (1,590 cm2) was larger than expected or previously reported, equal to 78% of the total surface area of the human neocortex. The unfolded and flattened surface comprised a narrow strip 10 cm wide but almost 1 m long. By applying the same methods to the neocortex and cerebellum of the macaque monkey, we found that its cerebellum was relatively much smaller, approximately 33% of the total surface area of its neocortex. This suggests a prominent role for the cerebellum in the evolution of distinctively human behaviors and cognition.
Pages: [1] 2 3 ... 10