Cardiac muscle

The heart muscle or myocardium (Latin myocardium ) forms the largest part of the wall of the heart. The heart muscle is surrounded on the outside by the epicardium and the inside of the endocardium ( endocardial ). The heart muscle is a hollow muscular having a specific reduction in volume with its contraction the cavity macroscopic ( loop-shaped, crosslinked ) structure.

Fine structure of cardiac muscle

Although the structure of the heart muscle has great similarity to skeletal muscle, it also has features that are known from the smooth muscles: it has, for example, medium-sized nuclei. Heart muscle cells ( cardiomyocytes ) normally contain a nucleus per cell, in rare cases, two, that is, they represent only functional point of a syncytium dar. with skeletal muscle collectively have the heart muscles to their regular structure of special striated muscle fibers and the system of rapid calcium ion influx through dyads ( in skeletal muscle triads) of terminal SR cisternae and T- tubules of the cell membrane. This structure is essential for the synchronization of the speed and powerful contraction and distinguishes the heart and skeletal muscles of the substantially smooth muscles.

Special features are the branching and connecting the individual heart muscle cells ( cardiomyocytes ) on glossy stripe ( intercalated discs or Disci intercalates, English intercalated disks ), whereas skeletal muscle precursor cells during Säugerembryonalentwicklung to real multinucleated syncytia merge ( and thus long muscle fibers form ). The glossy stripe included for pulse transmission gap junctions and stabilize the cell association and power transmission desmosomes ( maculae adhaerentes ) and Adhärenzkontakte ( fasciae adhaerentes ). New molecular studies of the intercalated disks show that typical desmosomal and fascia adhaerens - proteins ( in contrast to their respective localization in epithelia ) between mammalian myocardial cells do not occur separately and thus cardiac-specific adherens junctions of a complex mixed type ( Area composita ) prevail. The intermediate filaments of the cytoskeleton, which build on these cell - cell junctions, in this case consist primarily of desmin. Histologically also shows a slight trained sarcoplasmic reticulum as well as smaller tanks than in skeletal muscle cells. One speaks in this context of " dyad ".

Control

Specialized cardiac muscle cells that can trigger action potentials spontaneously self, accept the basic control of heart action. They are called excitation education system. The forwarding of the pulse on the real work is done by means of gap junctions muscles through specialized cardiac muscle fibers and not via nerve fibers. The adaptation of the heart muscle activity to short-term fluctuations in blood pressure via the Frank -Starling mechanism in the heart muscle itself, adapting to changing physical activity is controlled by the circulation center in the brain stem and the autonomic nervous system and is therefore subject also not the will of the individual.

Human cardiac muscle

The cardiac muscle of the ventricles of the human heart are 10-25 microns thick and 50-100 microns long. The number of cardiac muscle of the left ventricle, which provides the main pumping power is initially estimated to be 6 billion cells. Throughout life, the number decreases spontaneously and continuously and is specified in the elderly with 2-3 billion cells.