The Caption: Saw this awesome image on a hoodie. It captures my time in Toronto perfectly: studying medicine ...in the city! The image is of an ECG (electrocardiograph, one of the hallmark images of medicine) which shows the electrical activity of the heart. Hiding in this ECG is the city's trademark: the CN Tower.
The Comment: ECGs are incredible inventions because they allow doctors to see what the heart is up to. They may look like a line of squiggles, but each peak and dip represents an action of the heart. In short, the heart beats because the heart gets flooded with negative and positive electricity; the changes in electricity cause the different parts of the heart muscle to contract and relax causing the beat. There are four main parts (note that there are other segments which won't be discussed): the P wave represents the atrial depolarization (meaning the atria of the heart are getting more positive), the QRS complex means the depolarization (more positive) of the right and left ventricles, and lastly the T wave is the repolarization (more negative) of the ventricles. Image source here.