How the Heart Beats

More

The thomp-thomp of your heart beat will occur roughly three billion times in your lifetime. Over the last hundred years, scientists have learned a lot about the heart's mechanisms, as described in the dense, but clear video from the Guardian above. This is a summary of how a single heartbeat occurs, based on the description Michael Shattock of King's College London gives therein

Pacemaker cells at the top of the heart get things going, putting out an electrical signal on a steady but variable rhythm based on the body's needs. That signal spread down through the top chambers of the heart to the atrioventricular node, which directs the signal rapidly to the bottom of the heart. The pumping motion then spreads upward. Shattock noted this wiring makes for an efficient mechanism.

The electrical impulses that induce a heartbeat are generated by individual cells exploiting differences in the concentrations of sodium and potassium ions. (Ions are the name we give to molecules carrying an electrical charge.) There is lots of sodium outside the cell and relatively little inside whereas there is lots of potassium inside the cell and not much outside. Proteins open up channels through the cell membrane and like cold air rushing into a warm house, the sodium molecules push into the cell. Remember the molecules are ions, so a higher concentration of them makes the cell more positive. That's the electrical action that we call a nerve impulse. To end the activity, potassium channels open up and potassium rushes out of the cell, bringing down its positivity. Sodium is also pumped out of the cell through what is called active transport.

"How does that electrical activity translate into mechanical activity?" Shattock asked. The key to that action is calcium. During the period in which the cell's membrane is charged -- the action potential -- calcium enters the cell. The calcium triggers the release of more calcium from tiny bags -- sarcoplasmic reticulum -- filled with the element. Then, the calcium diffuses to the muscle filaments themselves and causes the actual movement. To relax the heart cells, the extra calcium that came across the cell membrane gets pumped out, and the heartbeat ends. Then, the process happens again and again until you die.

Jump to comments
Presented by

Alexis C. Madrigal

Alexis Madrigal is a senior editor at The Atlantic, where he oversees the Technology Channel. He's the author of Powering the Dream: The History and Promise of Green Technology. More

The New York Observer calls Madrigal "for all intents and purposes, the perfect modern reporter." He co-founded Longshot magazine, a high-speed media experiment that garnered attention from The New York Times, The Wall Street Journal, and the BBC. While at Wired.com, he built Wired Science into one of the most popular blogs in the world. The site was nominated for best magazine blog by the MPA and best science Web site in the 2009 Webby Awards. He also co-founded Haiti ReWired, a groundbreaking community dedicated to the discussion of technology, infrastructure, and the future of Haiti.

He's spoken at Stanford, CalTech, Berkeley, SXSW, E3, and the National Renewable Energy Laboratory, and his writing was anthologized in Best Technology Writing 2010 (Yale University Press).

Madrigal is a visiting scholar at the University of California at Berkeley's Office for the History of Science and Technology. Born in Mexico City, he grew up in the exurbs north of Portland, Oregon, and now lives in Oakland.

Get Today's Top Stories in Your Inbox (preview)

Sad Desk Lunch: Is This How You Want to Die?

How to avoid working through lunch, and diseases related to social isolation.


Elsewhere on the web

Join the Discussion

After you comment, click Post. If you’re not already logged in you will be asked to log in or register. blog comments powered by Disqus

Video

Where Time Comes From

The clocks that coordinate your cellphone, GPS, and more

Video

Computer Vision Syndrome and You

Save your eyes. Take breaks.

Video

What Happens in 60 Seconds

Quantifying human activity around the world

Writers

Up
Down

More in Technology

Just In