Wednesday, February 27, 2013

Nervous System

The nervous system is divided into Central Nervous System (brain and spinal cord) and Peripheral Nervous System (nerves, ganglia, etc).
Here's a little chart, courtesy of a great Physiology student:

Peripheral Nervous System Central Nervous System
nerves tracts
ganglia nuclei
Schwann cells oligodendrocytes


Part of the Peripheral Nervous System (PNS) is the involuntary part, consisting of efferent neurons controling visceral organs.  This is called the visceral nervous system, but more commonly known as:
Autonomic Nervous System
Autonomic = Automatic = Involuntary
Sympathetic & Parasympathetic divisions.  Here's a silly little video that shows the functions of each.


Sympathetic Division
Location: Thoracic and Lumbar regions of spinal cord

3 Kinds of pathways







Parasympathetic Division
Location: Brain, and Sacral region of spinal cord





Receptors






This is super fun, talks about the brain, gets deep and slightly philosophical, and mentions reflexes.  It's all about the brain! :)


The Science of Junk Food

Oh my...YOU NEED TO READ THIS AND SHARE IT WITH OTHERS... this New York Times article is very long but it will shock the socks off you.  I am ready to boycott Coke, Frito-Lay, Lunchables, and General Mills!  Anyone crazy enough to join me?  I'm quite honestly PISSED that these big companies do this crap and take advantage of the American public, because all they care about is MONEY.  (Pardon my language) Big business, you can go to hell.

Please share this with others!  Post it on Facebook and your own blogs, websites, etc.  People deserve to know about this.  (The science brain chemistry stuff in the article is also very fascinating, btw, and makes me angry that companies exploit it to manipulate consumers.)


http://www.nytimes.com/2013/02/24/magazine/the-extraordinary-science-of-junk-food.html?pagewanted=all&_r=3&

Monday, February 18, 2013

Reflexes

Reflex Arcs involve the spinal cord and leave the brain out of the picture, in order for the compensatory action to happen very quickly and avoid tissue damage.  Here is a short and sweet explanation:




Friday, February 15, 2013

Sand Grains

The geology nerd in me is feeling really neglected lately, being in a Biology major and all my recent posts have been about zoology.  So it's time to talk about sand.

For whatever strange reason, I LOVE sand.  In fact, I collect it.  I have samples of various sands from beaches in Hawaii my sister brought me, and a bunch I collected in Oregon on the beaches there and also some volcanic sand from a lava tube cave.  A good friend even brought me some sand from the Egyptian desert!  Oh, yes and one of my favorites - oolitic sand from the Great Salt Lake, as seen here:
5 mm view of oolitic sand from Antelope Island of Great Salt Lake (Source)
I love this sand because it is really soft.  The grains are tiny spheres built up by calcite being deposited, instead of being angular broken pieces from something that was eroded like most sands are.  For a simple explanation of ooids/ oolitic sand, see this post: http://biogeonerd.blogspot.com/2011/11/oooooooids.html

Sand Grains
This amazing website has beautiful pictures of sand taken up close - you owe it to yourself to check this out.  You can even order prints of the pictures!  (There are also extreme close-ups of parts of the human body, flowers, and food.) I know what I want for my birthday and Christmas.

The photographer - Dr. Gary Greenberg was kind enough to allow me to post the pictures here.  What a beautiful addition to this blog, I'm so thrilled!  Go to his site for other photos and great descriptions of each image.

Quartz sand

The spiny, glassy parts are spicules from a sponge! How cool is that!

This is the actual shell of a single-celled organism - foraminifera - from Japan

More forams



Sapphire crystal




This is a fragment of the mineral mica :)

This is volcanic sand!

The square one is a shell fragment



Superb, aren't they?  Thank you Dr. Greenberg for your inspiring work!  Here's the link again if you want to see more:
Sand Grains Gallery

Hey, look at this other cool thing I just found! This guy in New Zealand creates works of art on the beach, only to have them promptly erased by the surf - looks like he is having so much fun, I love his child-like curiosity and joy. :D

 

Thursday, February 14, 2013

Glucose Metabolism - Glycolysis through Kreb's Cycle

I was trying to think of a way to model these processes for the benefit of kinesthetic learners, so this is what I came up with using these cool toys my kids got from the kids' meal at Wendy's.  I hope this will help people visualize this and understand where all the Carbons from glucose go, and why on earth we care about all those NAD, NADH, FAD, and FADH2.


Here are the symbols for this model.  Purple= Carbon, Blue= Hydrogen, Red=NAD, Green=FAD, Orange=CoA enzyme


Below is a VERY simplified version of a glucose molecule.  This shows the 6 carbons because we want to see what happens to all these carbons.  There should be 12 Hydrogens and 6 Oxygens as well but for simplicity, I have only the carbons and 2 Hydrogens to illustrate one round of Redox reactions in glycolysis.

Glycolysis
Here we start with a glucose molecule and we will break it down.  For this demonstration I am ignoring the ATP, but just note that 2 ATP's go in to Glycolysis and you get 4 ATP out (so, a net production of 2 ATP).

Here are the reactants, or what goes in to glycolysis:



Next, we see that the glucose is broken apart (in half, basically)

And the NAD's come in to take the Hydrogens off to become NADH.  FYI, the glucose was "oxidized" because the electrons were taken off it, and the NAD was "reduced" because it got the electron (the hydrogen).  So, this is a Redox (Oxidation-Reduction) reaction.

Now we have two 3-Carbon structures, and two NADH's


The 3-Carbon moleucles are Pyruvate.

That's the end of glycolysis.  The NADH's are sent on to the electron transport chain at this point, so they leave.  Next the Pyruvates will be taken on and processed further in the next process, sometimes called the "Linking Step".  We will follow one pyruvate - keep in mind this process would happen twice for each glucose molecule since it splits in half into 2 pyruvates.

Oxidation of Pyruvate to Acetyl CoA (aka "The Linking Step")
So here is the Pyruvate going into the linking step.  By the way, this is the point at which metabolism has entered the Mitochondria.  Glycolysis takes place in the cytoplasm, and then pyruvate enters the mitochondria and that is where the rest of the processes take place.


I didn't do an intermediate picture on this one, sorry about that.  The NAD comes and harvests another Hydrogen (which is not shown on my simplified pyruvate), CoA is added and one carbon is removed and disposed of as Carbon dioxide.  Here are the products, notice the 3 Carbons accounted for:



And, we see here where each of the products are headed now:

Kreb's Cycle
Then we follow the Acetyl CoA into the Kreb's Cycle, here are the reactants:


I didn't attempt to show all the steps of the Kreb's cycle here, but there are many redox reactions taking place, turning NAD and FAD into NADH and FADH2.  Here's a diagram of the cycle, if you really want to see it:



 Here you see the products, and see all the carbons are accounted for (2 Carbons in, 2 Carbons out):


And, here are the other products, which are the electron carriers that then deliver it over to the electron transport chain:

Also, note that 1 ATP is made during the Kreb's cycle which is not illustrated.

See this post on the Electron Transport Chain for some great videos about what happens there.  NADH and FADH2 are the carriers that drop off the electrons to run the electron transport chain, which harvests 30+ ATP per glucose molecule.  That is why we care so much about harvesting Hydrogens from glucose so we can make NADH and FADH2 and send them on their merry way to the electron transport chain to make ATP.  ATP is the energy that cells use to do pretty much everything!  If you stop making ATP, you die.  End of story.


So, to sum up - see if you can go through and account for all the Carbons, Hydrogens and Oxygens of glucose (glucose is C6 H12 O6).  You'll see that 6 carbons go in, and 6 carbons come out.  (Remember that each glucose molecule becomes TWO pyruvates, so you would double the numbers from that point on.)

Also, 6 oxygens go in, and how many come out?  Yup, 6.  Go back and check if you want to see for yourself. :)

Now, how about the Hydrogens?  Go through and count to see how many are harvested.  Really, go look and figure it out...


....
Did you come up with 14?  Did you count wrong?  NO!  It is 14.  But there are only 12 on glucose right?  What's the deal?  The reason is we actually have one molecule of water (H2O) that goes in the Kreb's cycle during one of the steps (it's added to fumaric acid to make malic acid), and those are then harvested off.  So there are the extra 2 hydrogens!  :)  It's a beautiful thing.

P.S. if you notice on the diagram of Kreb's, it shows 2 H20 going in, but one of them does come back out, as shown on the more detailed diagram below.  2 water molecules in, 1 back out, that's a net of 1 H20, so there are your extra 2 Hydrogens still.  I circled the H20 for you to see:
Source

Hope that helps you understand and visualize metabolism better!  I'd love if you would leave a comment, and follow this blog if you feel so inclined.  Thanks, and happy learning. :)

Thursday, February 7, 2013

Action Potentials Up Close




Here is a pretty nice video showing action potentials and how they are propogated without decreasing.



Another one which shows the voltage-gated Sodium and Potassium channels:


This animated image is a bit difficult to follow because it's so fast, but seems like it could be helpful to someone, especially if you know how to slow it down (which I don't- if you know, please teach me!).  So here it is.
Source


Here are a few various visualizations I liked

Source - awesome nervous system/eye/ear post!

Source


Source - great post with lots of details!

The following images were all from this excellent source: http://mikeclaffey.com/psyc2/notes-neurons.html

First, we see the steps of the action potential and what is going on with the various channels:
Source


Next, here is a nice depiction of how the action potential moves down the axon and why impulses travel one-way.

Source


Lastly, we see how saltatory conduction works.  This is the fastest way to conduct an impulse because it gets to "skip" all that length of the membrane on the axon that is myelenated.

Source


There you are, folks, another deeper view into the amazing world of Action Potentials and your nervous system...isn't this awesome!?

(If you missed the first post, here is a link to it)
Action Potentials - What Make Your Brain Work

Wednesday, February 6, 2013

Membrane Potential

Membrane Potential is a separation of charges across a membrane.  In other words, it is positive on one side and negative on the other.

You could think of the "potential" as potential to do work.  When you have concentration gradients of ions, that is potential energy, like the elevator analogy.

Wikipedia

I haven't taken the time to actually watch these, but there are several videos on Khan Academy going over this and may be a great resource:
https://www.khanacademy.org/science/healthcare-and-medicine/heart-depolarization/v/membrane-potentials---part-1


At 1:57-3:00 of this video, it discusses chemical/ concentration gradient and electrical gradient and how they get to equilibrium (resting membrane potential for potassium).


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