Cardiac physiology

I wonder if physiology professors everywhere hack on about the same things: action potentials in muscle cells, both cardiac and skeletal, and the contents of the cell. So many things I’m more curious about, like the human genome and DNA, transcription, meiosis and mitosis, brain chemistry, kidney function, etc etc. But somehow it seems to me that the longest lessons always wind up being on action potentials, with their sodium and potassium channels, depolarization, and concentration and ion gradients. Maybe it’s just UofO and ESO. Maybe these are just the ones I understood the first time (thanks Grant and Greg!).

So let me explain it to you, to test my knowledge!

The heart has two types of muscle cells: autorhythmic and contractile. Autorhythmic cells control the electric signal that initiates the beat of your heart. Contractile cells cause the actual beat you feel, pumping blood through the body, and coordinate the timing. Both of these work in a never-ending cycle of depolarization and repolarization.

Hokay, so… in autorhythmic cells, like any cell, sodium is constantly being pumped out and potassium is constantly being pumped in by ion pumps that live in the membrane. They do this to Continue reading


the more I learn about cells, the more I think we are seeing a hundred reflections in a funhouse mirror

We’ve just finished the first two sections of physiology: Cells and Tissues.

Really fascinating.

We all learned about or heard of the cell, most of us more that 5 years ago. A gel-filled bag full of little blobs called organelles floating around, a large nucleus in the middle who is the boss, and a membrane holding it all together. Basically a bag of goo with lumps. Well, that idea got us a long way, but has turned out to not be very accurate. Textbooks need to be rewritten. The trouble is, the more we learn, the more we don’t know.

The organelles that were identified years ago still live in the cell, but better microscopes have shown there are other things within the cell as well. True, everything sits within a goo, but the organelles are fixed in place on a complex framework, like scaffolding, made of fibers called microtubules (green). When things need to be moved around within the cell, they don’t float randomly, but are actually “walked” down the framework by a molecular motor called dynein. Like little men in a factory! When they need to move to a new place, the microtubule scaffolding is remodeled, building paths to other places within the cell where things are needed. How? We don’t know.

Dynein – little men (1:13-1:40).

When cells need to make new proteins, which are machines (and in fact proteins make other proteins), they follow a code which is like a blueprint, with all of the materials somehow being available at that location and being brought to the protein to assemble, attaching one at a time, at high speed like a manufacturing plant.  How? We don’t know.

In a factory:

And in the cell:

Going back a ways, we all started off as one cell containing the DNA code, like the “blueprint.” From there, different parts of the blueprint were used to make different things, first making machines, then using those machines to make materials, which were used to make bigger machines. Some parts of the plans code for highly specialized machines. Some things are only made once. Some only at a certain stage of development. Some are used nearby, others far away. Some cells continue working for decades, others finish their task and self-destruct, getting cleaned up to make room for other work to be done. When you look at it as machinery, it’s highly organized and efficient, with everything very precise in order to work smoothly and seamlessly at high rates of speed on and on for years. How? We don’t know.

Now that we’re building microscopes strong enough to visualize all of these happenings, the similarities to things we’ve “discovered” and built are shocking. Take this flagellum, not unlike an outboard motor. We have only recently been able to visualize something this small, and yet we’ve been making and using it on a macro scale for years. How? We don’t know.

Are we not just clumsily redesigning the same machines on a grander scale? After physics discovering the “smallest” particles again and again, isn’t it possible that the divisions are infinite? And if so, wouldn’t this also work in the opposite direction? I can’t help but wonder, what is the bigger picture we are contributing to? Why do meteorites contain genetic material? Are we really all made of stars?

Just wanted to share a little of what’s bending my mind this month. Next we’re on to organ systems, can’t wait to talk muscles and bones for the next couple weeks. :)