Beth – Page 23 – The Beth Project

How does your heart beat?

This is a post about some things I learned this summer while I was interning in the mechano-electric feedback lab at the University of Oxford, working with computer models of hearts.

A heart removed from the body can be kept beating on its own for up to five hours, if you keep it in a fluid that contains the right dissolved ions and gases. The speed of your heartbeat can be increased or decreased by the nervous system, but creation of the beat is intrinsic to the heart itself.

Heartbeat starts as a rhythmic electrical impulse in a cluster of specialised cells. It's then conducted through the heart, causing the muscle cells to contract at specific times.

The chambers and vessels of the heart
Labelled diagram of the heart
Image from Wikipedia

Each beat of the heart progresses through several stages in sequence. First, when the heart is completely relaxed, the atria are at a lower pressure than the pulmonary vein and the superior vena cava. This pressure difference causes blood to flow into the atria. Then as the atria fill and the pressure inside increases, the mitral and tricuspid valves open, allowing blood to start flowing into the ventricles. Then the muscular walls of the atria contract, forcing more blood into the ventricles.

As the pressure inside the ventricles increases, the mitral and tricuspid valves close - isolating the ventricles from the atria - and the aortic and pulmonary valves open. The ventricles then contract, forcing blood out of the heart. The blood from the right side of the heart goes via the pulmonary artery to the lungs, and the blood from the left side of the heart goes to the rest of the body through the aorta.

Animation of conduction through the heart
Animation of electrical conduction through the heart
Adapted from Wikipedia

The sinoatrial (SA) node is where the electrical signal is created. The impulse is then conducted through the working cells of both atria, inducing them to contract. The signal then passes slowly through the atrioventricular (AV) node, down through the bundle of His and the right and left bundle branches, then up across the purkinje network, and finally through the working ventricle cells. The ventricles then contract from the bottom upwards, and then the heart relaxes until the next beat.

The speed and route that the impulse takes to pass through the heart are very important for proper functioning of the heart. This, and the creation of the beat, are emergent properties of the voltage-gated ion channel systems in heart cell membranes.

Reference: Human Physiology - From Cells to Systems by Lauralee Sherwood (5th Ed) ISBN 0534395015, p.303-330

Things I've been up to in 2011

"Bring It, Don't Bin It" happened: we collected a load of clothes, toiletries, kitchenware and bedding (which, as you can see above, we promptly sat on) from departing Erasmus students and had a yard sale at the union. The profits and the rest of the stuff went to St. Vincent's, a Sheffield homeless charity. We got the electrical stuff PAT-tested, too! There was a second collection in June as the rest of the students left - unfortunately I couldn't attend, as I was at BarnCamp. I'm really pleased with how this project turned out.

I played in the National Concert Band Festival with the Sheffield University Wind Orchestra. We won a gold award, which sounds great until you realise that there was also a platinum award, and somehow managed to get to Glasgow and back in a single day. What madness.

BarnCamp - the annual techheads-go-camping-and-drink-too-much-cider extravaganza - was awesome (if very, very wet). My favourite workshop was on fractals, by Mike Harris. He was showing us the <canvas> element in HTML5, and how it can be used to make things like Mandelbrot sets. There are some great photos on flickr.

Incidentally, the person who coined the term "fractals", Benoit B Mandelbrot died last year. The B in his name stands for Benoit B Mandelbrot.

Lots of people I like have died recently. Janet McCleery, my awesome singing teacher - Dennis MacDonald, a fellow volunteer at the BitFixit Cafe (and a million other community projects) - Charlie Dickinson, a cracking lad I knew at school - and my lovely friend Brian Jackson, who I miss rather a lot. So that's not been great.

I found out today I have a confirmed place on my Mechanistic Biology Masters course for next year, so that's me sorted until next September. Last week I started my internship for the summer at Oxford Uni working on computer models of heart cells. I didn't know much at all about electrophysiology until last week so it's been a pretty steep learning curve! I'm really enjoying the challenge. Happy summer, everybody.

Free software talk

Tux mug
source

I did a talk this morning about free software with my friend, scary brainy sysadmin Alan. Alan covered the philosophy of the free software movement, and I talked about the practical ways people could start using free software every day.

I thought I'd make a post about some of the things I linked to and talked about.

We had a look at AlternativeTo, which is a website that lists different programs you might want to use (for example Photoshop) and lists some alternatives (for example, the GIMP). You can select "Open Source" from the drop down box to see only open source software, most of which is also free.
Portable Apps are really nifty programs. You can install them onto a USB pen drive and use them on any Windows computer. It's really handy to have, for example, Firefox with all of your bookmarks and add-ons ready to use when you're using a friend's computer or at work. Also if your job is particularly boring they have a massive list of games.
I have already mentioned Firefox and the GIMP, but some other programs to look at are LibreOffice, which has all the functionality of Microsoft Office; Thunderbird email client; Pidgin chat client (you can use it instead of MSN messenger, AIM, Yahoo! etc.); VLC media player which can handle pretty much any type of video or audio file; Audacity for editing sound files (I used it for my podcast).
If you want to run your whole computer on free, open source software, you can use some kind of GNU Linux instead of Windows or Mac OS X (you can also have both Linux and Windows/OS X on your computer at once without slowing it down). There are lots of different flavours, or "distributions" of Linux. You can use this Linux Distribution Chooser quiz to find out which one is the best for you, based on your computer knowledge and what you want to use it for.
For a Linux beginner I usually recommend Ubuntu, which is really user-friendly and has a really attractive desktop. It will run on most machines, but for super old computers, Debian might run faster, and is a bit more stable.
If you want to try out Ubuntu before installing it, you can make a LiveCD or LiveUSB and play around with it, without changing anything on your hard drive.
This isn't really related, but Alan's presentation was made using S5: A Simple Standards-Based Slide Show System, which is a really cool HTML-based way of doing slideshows. I'd never seen it before, but I think it's great!

Free software's pretty awesome. It doesn't cost you any money, and you can distribute it how you like. Anyone can see the source code, and anyone can submit revisions to it, which means that when there's a problem with the program it's often fixed really quickly by the community. There's always a huge number of helpful users on the internet who make tutorials and answer questions.

It's not just on the internet you can get help either - in Sheffield there's Access Space near to the showroom cinema. They're a great bunch of techie arty people who will help you out with using and installing free software. There's also the BitFixit Cafe in the Burngreave area of Sheffield, which I volunteer at. We're open on Saturdays between 12 and 3 at 268 Verdon Street, and we're happy to install things, fix problems, and eat biscuits.