Our first article in this section considers the structure of cardiac muscle. Cardiac muscle is similar to skeletal muscle in that it is striated and that the sarcomere is the contractile unit, with contraction being achieved by the relationship between calcium, troponins and the myofilaments. This article will consider the structure of cardiac muscle as well as relevant clinical conditions. It will detail the structural differences that differentiate it from cardiac and smooth muscle. Arguably the most important feature of cardiac muscle is its intercalated discs and gap junctions. The disks act as the Z band would in skeletal muscle, demarcating where a cardiac muscle cell meets the next.
The transverse portions form adherens-type junctions (attachments) and desmosomes, holding the muscle cells together, while the lateral portions form gap junctions that allow for quick conduction of action potentials. This is crucial to allow the heart to contract in a coordinated manner and pump the blood.
Our second article in this section considers the mechanism by which cardiac muscle contracts. As in skeletal muscle, cardiac myocytes contract according to the sliding filament theory of muscle contraction. In this article, we will look at the process of calcium-induced calcium release and the electrical coupling of cardiac myocytes.