Wednesday, February 20, 2013

put your science panties on (part 1)

Let me warn you before you embark on this post: it’s a little more technical than usual. We’re going to cover the mechanics of both your nervous system and your muscular system, in our first ever two-part blog post (ooooh, aaaaaah!). So unless you have a solid 20 minutes or so, I suggest saving this one until you are at home with a cup of hot tea with Wheel of Fortune on in the background.

It’s easy to avoid thinking about how your muscles work because it can be an overwhelming thought. How complex they must be to be capable of lifting heavy things and also finite tasks like writing! And even MORE mind-boggling is the system that connects your brain to each and every muscle cell in your body. How in the cornbread hell can a simple thought turn into an intent, and then turn into an action? How can you go from thinking about scratching your head, to intending to scratch your head, to scratching your head? It is confounding.

Your brain has highways reaching out to all of your skeletal muscles. These highways are your nerves. Most of them exit your skull and travel along your spine in that clump called the spinal cord. From there, they branch out to your muscles.  A single one of these nerve cells is called a motor neuron, and is not a blob of a cell like you usually think of.  It has a body and a long skinny “stem” called an axon. They’re long and skinny because- well, they’re highways! In fact, the longest single neuron you have runs from the base of your spine to your toes- up to a meter long. Think of the motor neurons a giraffe has!
Figure 1: A single neuron.

These highway nerve cells are uniquely structured for carrying signals- chemo-electric signals- from your brain to your muscle cells. Your brain tells your muscles what to do via your nerve signals. But these signals are not “encoded” with information- one signal does not vary from the next, nor do they vary in strength. It’s kind of like binary code- it’s either a 1 or a 0. In this case, there’s either a signal, or there’s not. Your neuron fires, or it doesn't. One single signal is called an action potential.

An action potential is basically a change in voltage of the membrane of a nerve cell. It’s like this wave of voltage that travels along one nerve cell, setting off the one after that, and the one after that, and the one after that, and- well, you get the picture. But these nerve cells- their membranes in particular- are specially built for carrying action potentials.

Alright y’all. Time to put your science panties on. It’s about to get real up in here.

The inside of the cell is negatively charged, in respect to the outside of the cell. Positively charged potassium (K) and sodium (Na) ions are floating around, both inside and outside of the cell. There are little pumps in the membrane are constantly pumping these ions against their concentration gradients in and out of the cell to maintain a high concentration of K and low concentration of Na inside the cell- which maintains an internal charge of about -70 millivolts. This is called resting potential.

Figure 2: The basic set up of the axon of a neuron: The movement of Na+ and K+ ions  through channels and a pump
across a the membrane cause depolarization, repolarization, and hyperpolarization of the cell membrane (aka an action potential)

Now, let’s say the neuron’s dendrites become excited enough to set off an action potential. Little voltage-dependent sodium channels will open up, allowing sodium ions to diffuse along their gradient- into the cell. This influx of positively charged ions raises the inside voltage. This part is called depolarization, since the cell is becoming, well, depolarized.

Once the inside of the cell reaches about 40 mV (notice, that number is now positive!), sodium channels close and their neighboring voltage-dependent potassium channels open. Then, the potassium ions have their turn to diffuse along their gradient- out of the cell. This exodus of positively charged ions then causes the intracellular voltage to drop- bringing it back down into the negatives. These potassium channels are a little sluggish, though, and take a while to close. The cell hyperpolarizes a little past the original -70 mV, but is corrected quickly by the trusty Na/K pumps.

This process happens as a wave, traveling down the axon of a neuron. To help the process, a material called myelin wraps around the axon (Fig.1- the white bead looking things). Myelin is white (that’s why the neural tissue of your brain is white… white matter!) and is an insulator. This allows the action potential to skip right through the insulated bits, speeding up transmission to lightening fast speeds. That time you almost dropped your phone in the toilet but caught it right in time? Yeah, those lightening fast reflexes were thanks to myelin.

Once a neuron propogates an action potential all the way down to the terminal buttons, it sends chemical signals (neurotransmitters) out to the next neuron in line and excites its little dendrites- starting the process over. This occurs all the way down to the intended muscle site. And there, the muscle must take this action potential and turn it into kinetic motion. And kinetic motion is WAY more exciting than ion diffusion- so, stay tuned!

Now, I know that if you’re reading this part, you’ve read this entire blog post. And for that, faithful reader, you deserve A TREAT. To claim your treat, simply leave a comment stating your name, and I will write you a poem. And yes, it will hurt my feelings if no one takes me up on my poetry offer. FYI.

Thursday, February 14, 2013

cheers to love

You know the moment you meet a special someone and your face flushes when your eyes meet? Or the accidental brush of a hand that makes you jittery and you start to sweat? That hug that makes your heart pound? These are all perfectly normal responses to being smitten.

In the spirit of Valentine’s Day and romance, we’re going to talk about what happens when you get a little frisky. As embarrassing as the topic may be, sexual arousal brings about fascinating responses, born from primal origins long ago in our evolutionary history. Don’t worry; it’s all PG-13.   

Get it girl. (
Flushing is an especially functional reaction. Increased heart rate forces blood into vascular dermal tissues such as your cheeks. A nice rosy glow communicates to your crush that you are interested, healthy, and sexually operative. (And thanks to the makeup industry, you can now fool people into thinking you are all of these things! Stupid suckers.)

Sweating may seem like a sexual deterrent (after all, pit stains don’t really say “come hither”), but is actually working for you in a romantic setting. You have two types of sweat glands. Eccrine glands are all over your body and really only secrete water and salt. Appocrine glands are found in your armpits and crotchal area and are connected to hair follicles. It is from these appocrine glands that pheromones are emitted. When sweating increases upon sexual arousal, it is your body’s way of dispersing those pheromones into your immediate environment. Though it may be only subconscious, the person of interest will pick up on these smells and (hopefully) react positively to your smell.

When you let your honey into your personal space, you are certainly allowing yourself to be vulnerable. Goosebumps that arise from this sort of closeness are remnants of the ancestral reaction to a potential threat. Think of a porcupine putting up its quills, or a cat’s hair standing on end. You’re on guard and your senses are heightened. Makes sense.

Thank you for setting
unachievable pupil standards,
Belle. Thanks.
My favorite sexual reaction is pupil dilation. Pupil dilation occurs as a means to heighten sight sensitivity, and functions similarly to the goosebumps as a way of being “on guard.” Studies show that men consistently prefer women with big ole’ cartoon pupils. The bigger the pupils, the stronger the attraction. However, this is not mutual. Studies by Tombs and Silverman (2004) show that women prefer men with moderately dilated pupils. They suggest that men with fully dilated pupils are more emotionally charged and pose more of a threat, tending towards violence or forcible acts. It has also been shown that females’ pupil size varies on a monthly cycle- peak size correlating with peak fertility (Caryl et. al).

Our bodily systems are amazingly and elegantly coordinated. Pupil size changing with fertility? That's amazing.

All of this being said, I think the distinction between lust and love must be made. All of these physiological responses are lustful. Love requires some extra ingredients that I’m not sure biology can explain.

Cheers to cool biology and love, friends. Hope you have a wonderful Valentine's Day.

Caryl, Peter G. Jocelyn E. Bean, Eleanor B. Smallwood, Jennifer c. Barron, Laura Tully, Michael Allerhand. Women’s preferene for male pupil-size: Effects of conception risk, sociosexuality and relationship status. Personality and Individual Differences. Volume 46 Issue 4, March 2009. Pg. 503-508.

Tombs, Selina, and Irwin Silverman. Pupillometry, a sexual selection approach. Evolution and Human Behavior 25 (2004), Pg. 221-228.

Monday, February 4, 2013


Currently, I am lying on my couch eating King Cake and watching The Two Towers (extended edition, eh hem). Just now, Merry and Pippin escaped the dinner conversation between the quibbling Uruk hai and orcs, and haunting Fangorn Forest towers in the background. Ah, Fangorn Forest- home to that loveable Treebeard. He’s so funny. Mostly, because he is a tree. A walking, talking, poetry-loving tree, who thinks it’s easier to travel south because “somehow, it feels like going downhill.”

A big part of Treebeard’s strength as a character is just this- he is a tree that can move and walk and talk. In the films, his entrance surprises and delights us when Pippin realizes he is clinging onto the face of a conscious tree. It seems contrary to us that a plant should locomote and exhibit behavior of any type. While I am (sadly) unaware of any actual Ents in existence, I am aware of a few plants that are capable of motion.

Sensitive plant, Mimosa
Those cute little sensitive plants that grow in the grass, Venus Fly Traps snapping their prey, fields of sunflowers that begin the day facing the east and end it facing west; moonflowers that close up at dawn and reopen at dusk; the world of plants is surprisingly animated.

Without muscles, ligaments, or tendons, how do they do it? When you touch the leaves of a sensitive plant and they close up in a matter of seconds, what do you think is causing the motion?

In most cases, a change in turgor pressure is the mechanism. Turgor pressure is simply the water pressure within a plant cell. By localized swelling in turgor pressure, the shape of a leaf may be altered. For instance, if the cells of just one side of a leaf swells, the whole structure will become bent (Fig. 1). Conversely, if a bunch of cells expel their water, that area of the plant will collapse.

Figure 1: A.) Even turgor pressure B.) Increased turgor
pressure on top layer forces leaf to bend

The stimuli for these pressure changes vary. Sometimes, sunlight exposure will trigger cell swelling (cwelling, new word? I think so). Other times it is a reaction to sensory hairs called trichomes, or simply pressure setting off an ionic message through the cells like dominos. It varies from species to species.

If we could ever get our hands on an Ent, wouldn’t it be something to see if their physiology operates on a turgor pressure differential system? That Isengard and Soromon were defeated basically by the simple act of water diffusion? 

Why yes, Aragorn. We should go get drinks later.