What Is the Myocardium?

The heart muscle (cardiacmuscle) is a muscle tissue composed of cardiac muscle cells. The structure of cardiomyocytes and skeletal muscles is basically similar, and there are also stripes. Broadly defined myocardial cells include the specially differentiated myocardial cells that make up the sinoatrial node, intraatrial bundle, atrioventricular junction, atrioventricular bundle (ie, Heath bundle), and Purkinje fibers, as well as general atrial and ventricular muscles. Working cells. The first five make up the cardiac pacing conduction system. They contain very little or no myofibrils and therefore have no contractile function. However, they are self-regulatory and conductive and are the functional basis of cardiac autonomic activity; the latter two are contractile and are the functional basis of cardiac diastolic activity.

Chinese name: Myocardium
Foreign name: cardiac muscle
Nature: A muscle tissue made up of myocardial cells
Including: Sinus node, intraatrial tract, atrioventricular junction

Features: Autonomy and Conductivity
Features: Functional basis of cardiac autonomic activity
Structure: The structure of cardiomyocytes and skeletal muscles is basically similar
Pinyin: Xin Ji

Myocardial structural features

The structure of cardiomyocytes and skeletal muscles is basically similar, and there are stripes, but they have the following characteristics in structure:

Myocardial disc structure

Cardiac cells are short columnar and generally have only one nucleus, while skeletal muscle fibers are multinucleated cells. There is a disc structure between the cardiomyocytes. Here, the cell membrane is embedded in unevenness, and is specially differentiated to form desmosomes, which are closely connected to each other, but there is no continuous protoplast between the myocardial cells. Myocardial tissue has been mistaken for syncytium in the past, and electron microscopy studies have shown that there is a clear diaphragm between myocardial cells, which has been corrected. The diaphragm of the myocardium is conducive to the transmission of excitability between cells. On the one hand, because the structure has low impedance to the current, the excitation wave is easy to pass; on the other hand, because the place is connected in a gap, there are 15-20 angstrom hydrophilic tubules inside, which can allow the calcium ion plasma to pass through. Therefore, although normal atrial muscles or ventricular muscle cells are separated from each other, they are excited at the same time for synchronous contraction, which greatly improves the effectiveness of myocardial contraction and functionally reflects the characteristics of syncytia, so it is often called "functional syncytium".

Myocardial cross section

The nucleus of cardiomyocytes is mostly located in the middle of the cell, and its shape is oval or rectangular, and its long axis is consistent with the direction of myofibrils. Myofibrils run around the nucleus, and the ends of the nucleus are rich in sarcoplasm, which is rich in glycogen particles and mitochondria, in order to meet the needs of myocardial continuous rhythmic contraction activities. In cross section, the diameter of cardiomyocytes is smaller than that of skeletal muscle, the former is about 15 microns, while the latter is about 100 microns. From the longitudinal section, the sarcomere length of cardiomyocytes is also shorter than that of skeletal muscle.

Myocardial ultrastructure

Observed under an electron microscope, myocardial cells can also be seen in myofibrils, transverse tubules, sarcoplasmic reticulum, mitochondria, glycogen, fat and other ultrastructures. However, myocardial cells are different from skeletal muscles; the thickness of myofibrils of cardiomyocytes varies greatly, ranging from 0.2 to 2.3 microns; at the same time, thick myofibrils and fine myofibrils can migrate to each other, adjacent They are so close to each other that the boundaries are unclear. The horizontal tubules of myocardial cells are located at the level of the Z line, and a variety of mammals have longitudinal and axial extensions, with a tube diameter of about 0.2 microns. The transverse tubule of skeletal muscle is located at the junction of A-I band, without longitudinal axial extension. The diameter of the tube is larger, about 0.4 microns. The sarcoplasmic reticulum of myocardial cells is in the middle, there are not many lateral terminal pools, and it is not widely attached to the transverse tubules. In short, cardiomyocytes and skeletal muscle cells each have their own characteristics in morphology and function.