Page 2 - Myocytes
Skeletal striated muscle is a simple thing. All the myocytes pull in the same direction and are packed in orderly, parallel lines in the muscle with a minimum of connective tissue between them, as in biceps on the left above. They rely on their hinges and pulleys and on opposing muscles for subtlety of movement.
The tongue is a notable exception, achieving variability of movement by having opposing bundles of aggregated myocytes woven into its framework. In order for these bundles to have some freedom of movement, there is a lot of connective tissue between them, some of it fat.
The left ventricular myocardium has a myocyte arrangement is somewhere between the tongue and the skeletal muscles. Batches of myocytes clearly pull mainly in one direction, but branch and angle to a degree hinting at more complex stresses present. Towards the top right hand of the image, the general direction of alignment has shifted slightly. Strands of connective tissue spaces hint at a need to have some freedom of movement between cells or small aggregates of cells.
Because a myocyte is of fixed volume, if it contracts along its major axis, it must bulge in its transverse dimension. This bulge will contribute to transverse thickening of the left ventricular wall, but as we will discuss soon, it is far from enough to explain it completely. A skeletal muscle is free to bulge sideways, as body builders will demonstrate with pleasure. The myocardium is unique in that its walls are not free to bulge outward. Their bulge is converted into an accelerated inward movement of the endocardial border, and this is what we will explore in the next few pages.