Cells hate calcium!

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I always tell my students to remember these three things:

Cells hate sodium ions (Na⁺).
Cells hate calcium ions (Ca⁺⁺).
Cells love potassium ions (K⁺).

OK, that's not literally true.  As far as we know, cells are not conscious and therefore do not love or hate anything.  But they sure act like they do!

Think about it.  All living cells have Na-K pumps that pump Na⁺ out while at the same time pump K⁺ in. When Na⁺ leaks into the cell, out it goes.  Likewise, when K⁺ leaks out of a cell, it's pumped back in.

As far as cells are concerned, Na⁺ is like a rattlesnake and thus is repulsive and must be gotten rid of when it sneaks in.  And K⁺ is like a puppy that the must be brought in and cuddled.  Should K⁺ escape to the cold, cruel world outside a cell, it should be brought back inside and cuddled.

Knowing these facts about sodium and potassium ions is useful to A&P students.  Why?  Because it helps explain where these ions are likely to be found in the human body:

• If you're looking for Na⁺, look in the solution outside the cell (extracellular fluid). You won't find much Na⁺ inside the cell, because it is continually pumped out of the cell.
  
  
• If you are looking for K⁺, don't look in the extracellular fluid. You'll find very little K⁺ there. Most of the K⁺ will be inside the cell (intracellular fluid).
  
  

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The fact that there are these sodium and potassium ion concentration gradients help explain the concept of membrane voltage (membrane potential). This idea, then, is the foundation of understanding nerve impulses and muscle stimulation.

During a nerve impulse, Na⁺ rushes into the nerve cell because of the concentration gradient described above (most of the sodium is outside the cell). This gives the membrane a temporary inside-positive charge… and that's what a nerve impulse is. The normal membrane voltage is restored quickly when K⁺ is allowed to rush out of the nerve cell, thus moving the net positive charge to the outside of the cell membrane.

All living cells have calcium pumps that pump calcium out of the cell.  Some calcium pumps also pump calcium into sacks (the smooth ER).  To a cell, Ca⁺⁺ is like a cobra. When it leaks into a cell, and it will, it is pumped out quickly or pushed into a sack.

Knowing this fact about calcium ions is useful for understanding many different concepts in A&P.

For example, muscle fibers pump calcium ions out of the plasma membrane (sarcolemma) and into the sarcoplasmic reticulum (SR, a form of smooth ER). When the muscle membrane is stimulated (see the paragraphs above), the Ca⁺⁺ comes rushing into the intracellular fluid from the SR and/or from the extracellular fluid. Ca⁺⁺ immediately binds to the cytoskeleton, which then produces muscle contraction.

A similar thing happens at the end of a neuron when a nerve impulse (see the paragraphs above) gets to its farthest distance and permits Ca⁺⁺ to flow into the cell. The Ca⁺⁺ binds to the cytoskeleton and thereby triggers the movement of vesicles filled with neurotransmitter. These vesicles crash into the plasma membrane and release neurotransmitters by exocytosis, thus allowing them to signal another cell.

Ca⁺⁺ gradients are also key to understanding how many hormones trigger their target cells. It even helps explain some of the functions of sperm cells and egg cells during human reproduction.

So you can see that this idea of cells hating sodium and calcium ions and loving potassium ions comes in pretty handy when trying to understand many of the concepts of human physiology.

Penile fractures and pop culture

Of course you want to apply your increasing expertise in human anatomy and physiology to your experience of popular culture, right?

You've already probably caught yourself second-guessing some of the diagnoses of Dr. House's team . . . at least those lame ones offered during the first fifteen minutes of an episode. Or the really off-the-mark versions of human structure and function woven into episodes of Fringe.

Get used to it. Apparently, the big money that goes into TV and movie productions does NOT go to anyone who passed a basic A&P course!

Dr. Patton's Theory of Media Science (Dr. P's TMS) . . .which I just made up after years of mulling it over . . . and shouting it to my television screen . . . states that

"biological accuracy of a science-based fictional media production is inverse to the total budget for special effects in the production. "

My hope is that producers will eventually recognize the validity of my theory, and the growing population of A&P-educated viewers who can spot a stupid science "fact" that really doesn't have to be there to make the story flow or to keep the special effects within budget or allow for a snappy movie or episode title.

Then these cutting-edge producers will spring for a modest fee for an A&P consultant in each production. Which will spur an increasing demand for graduates of my A&P courses. Which will increase my job security. And then perhaps one day this trend will help me find a part-time job when I retire . . . perhaps an A&P consulting job that also involves brief, well-paid, guest-starring roles and sharing beers and pizza with my favorite TV and movie stars.

However, a recent episode of Grey's Anatomy (season 5, episode 513) brought up an anatomical issue that is rarely discussed in A&P courses . . . and so one might wonder "can this be true?!" Or even, "PLEASE tell me this cannot be true!"

Yes, my friends, one CAN break a penis. In fact, it's a more common injury than most people suspect.

Why don't we hear about it more often?

First, if you or your partner has broken a penis, would you be talking it up everywhere you go . . . as one might with a broken leg? Second, let's face it . . . one would have a cast that's out there asking to be asked about, right? Third, at least in my part of the world . . . we simply don't talk much (out loud, in public) regarding anything having to do with sex. (In fact, some reading this will shudder at my bringing it up in a blog for students . . . if they've even read this far.)

Why didn't your A&P teacher tell you about this? So you could fulfill your role as A&P expert as you watched the episode with friends or family? First, you probably haven't gotten to that part of the course yet. Second, when you do your instructor will likely be behind schedule and won't have time to tell you interesting stories about penis fractures. And third, in my part of the world at least, your professor doesn't want to have to take time to deal with formal complaints from horrified students who don't realize that any part of the body IS an appropriate topic of conversation in an A&P class.

Want to know more?

Try this straightforward . . . and easy to understand . . . article from Scientific American.

OUCH! Can you really break your penis?

You'll learn a lot of useful A&P, you'll be able to contribute to the inevitable classroom discussion on this topic, and you'll be all set for a future career as a TV/movie consultant after you successfully complete your A&P course!

Want to know even more useful (and possibly career-enhancing) facts related to the sex organs? Then check out the book Skin Flutes & Velvet Gloves: A Collection of Facts and Fancies, Legends and Oddities About the Body's Private Parts


By the way . . .
The television show Grey's Anatomy is a word play on the title of a famous medical anatomy text by Henry Gray called Gray's Anatomy. Notice the difference in spelling. Originally published over 150 years ago (1858), the current edition remains a leader among the best available references to the human body (and now comes in many different variations to suit different needs). In case you need more facts to bolster your standing as the local A&P expert among your television-viewing crowd.