The human heart is amazing. It’s like the energizer bunny of organs: it just keeps going and going and going… It knows its job and it does it: PUMP. Pump that blood! Keep things movin’ and groovin’ so that everyone’s happy. In fact, it is so determined in its efforts that it doesn’t even need anyone telling it what to do. If you were to remove a heart from a living person (don’t do that, that’s bad), it would just keep on beating. And we thought our brains were calling all the shots! Your brain can affect the rate the heart pumps at, but the heart doesn’t need any stimulus to pump in the first place. Lub dub… lub dub… lub dub.


I thought I could wave goodbye to physics after the MCAT, but it turns out that our bodies are some of the most intricate electrical systems imaginable. Muscles move because of changes in charge differences, our brains conduct an incomprehensible orchestra of signaling, and our hearts pump because of ions moving in and out, in and out. When you want to move your pinky finger, there’s a sequence of electrical signals that occur. I’m sure a lot of crazy stuff happens in your noggin (we haven’t had neurology yet, so it’s all a mystery to me up there), and then an electric signal gets shot down the very long tunnel of a nerve. One single cell can extend all the way down your arm to carry the current to the right muscle. Once that current gets to the end of the nerve cell (or neuron), it triggers little chemical messengers to jump across the space between the neuron and the muscle tissue. The message is received and the response is more electrical firing, but this time within the muscle cell. All the right charges and shocking will cause your muscle to contract and your pinky to do its little pinky dance.

The electrical changes within cells can be very diverse, but most changes that result in signaling are remarkably similar. When a cell is stimulated to “fire,” it’s called an action potential. The currents and polarization of the cell have a characteristic shape to them when you graph them out (science geeks just love their graphs). Usually cells have to be activated by other cells in order to fire an action potential. For example, muscles don’t just contract by themselves; they have to be shocked by a neuron in order to start their own electrical signaling. So their graph is flat along the bottom because they’re resting and waiting for something to stimulate them.

The crazy thing is that heart cells don’t need the initial push; they have all the machinery to essentially shock themselves into action. There are two main types of cells in the heart: pacemaker cells that get the initial shock going without an impulse from your brain, and myocytes (or, as I think of them, squeezy cells) that keep the signal going and actually contract the heart.

The way the pacemaker cells work is the reason I’m writing this entry. They have these channels in their membranes that are continuously letting ions through until they reach a threshold and they experience an action potential all on their own. Most cells have to be pushed to the threshold by a neuron, but these guys just leak and leak and leak until they let themselves get there without any outside help. So their graph has this lovely slope to the bottom of it; it doesn’t rest, it’s continually moving towards action. Even after the full shock of an action potential, a neuron experiences naptime where they physically can’t be pushed to that threshold or experience another shock. But the pacemaker cells don’t give themselves a nap, they just start leaking again.

Are you ready for the metaphor smackdown? I am like those cardiac cells, reaching my stress threshold and “exploding” on a regular basis. Before med school, I was like the squeezy cell: I would reach my limits but it usually took an external push to get there. In med school, I’m the pacemaker cell. There’s no avoiding the constant leak of stress into my life and it’s only a matter of time before I reach my action potential. Even after an exam, when I should be hyperpolarized and immune to repeat stimulation, I feel myself getting amped up and I know that it’s only a matter of time before it happens again.

Since I’ve recognized the upward slope and the constant movement towards another stress-bomb I’ve tried to do things to at least get the bottom of my curve lower, to give myself more time between each action potential. Whether it’s going on a bike ride or seeing a cheesy horror movie with the people closest to me, I still know I’m leaking stress into my system. When I attempt to relax, I’m leaking it in because I’m thinking about how I could be making progress in one project or another. Yet when I’m studying or working with extracurricular stuff, I’m climbing the slope towards a personal breakdown.

The balance is there, I just have to find it. For now, though, I’m stuck on the upward slope of that action potential. Leak leak leak… SHOCK… leak leak leak… SHOCK. I think my heart was built better for this kind of repetitive stimulation than my poor brain.


04/25/2012 15:29

Good stuff Julie. Keep on pumping!

04/26/2012 10:07

Well, try not to stress yourself out even more by obsessing about "finding the balance"; just ride that crazy med school/life roller coaster and have a great time doing it (even with no hands sometimes!).


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