Tissue that capable of conducting action potentials?
it happens through the desmosomes that conect the myocytes Intercalated discs (IDs) are complex adhering structures which connect single cardiac myocytes to an electrochemical syncytium (in contrast to the skeletal muscle, which becomes a multicellular syncytium during mammalian embryonic development) and are mainly responsible for force transmission during muscle contraction. Intercalated discs also support the rapid spread of action potentials and the synchronized contraction of the myocardium. In the old textbook dogma IDs are described to consist of three different types of cell-cell junctions: the actin filament anchoring adherens junctions (fasciae adhaerentes), the intermediate filament anchoring desmosomes (maculae adhaerentes) and gap junctions. Gap junctions are responsible for electrochemical and metabolic coupling. They allow action potentials to spread between cardiac cells by permitting the passage of ions between cells, producing depolarization of the heart muscle. However, novel molecular biological and comprehensive studies unequivocally showed that IDs consist for the most part of mixed type adhering junctions named area composita (pl. areae compositae) representing an amalgamation of typical desmosomal and fascia adhaerens proteins (in contrast to various epithelia)[citation needed]. The authors discuss the high importance of these findings for the understanding of inherited cardiomyopathies (such as Arrhythmogenic Right Ventricular Cardiomyopathy, ARVC). some nerves have this capacity as well
Why do you get ECG ST elevation with a full thickness myocardial infarction?
In my understanding, the ST segment is where the ventricles are contracting. Why do you get electrical activity (shown by ST elevation) in this segment with a myocardial infarction (a STEMI)?
Does the cardiac conduction system work more like nerves or more like wires?
Heart has pacemaker cells [Sino-Atrial (SA) node] which generate action potentials spontaneously; this sets the rhythmic heart rate. The signal for the cardiac muscle fibres (cardiac myocytes) to contract comes not directly from the nervous system , but from pacemaker cells of SA node. Cells of the SA node depolarize the atrial myocytes. Cardiac myocytes which generate force are connected to each other by gap junctions, so depolarization of one cell quickly spreads to the neighbouring cells, action potentials are generated by membranes of atrial myocytes.The green fibres shown around the atria in the figure below, conduct action potentials to the atrio-ventricular node (AV node). In ventricals, myocytes are also depolarized by the conducting fibres. Purkinje fibres are like heart cells but with very little contractile material. They are larger and conduct action potentials faster, more like nerves. Purkinje fibers act as axons designed to propagate an AP rapidly without depolarizing surrounding ventricular septal tissue significantly. There are specific areas where the conducting system interacts with contractile muscle fibres to depolarize contractile cells.All myocytes generate action potentials. Essentially, all cells in the heart generate action potentials, wires do not generate action potentials. However, when current flows from one cell to the others via gap junctions, that flow is more like one along a wire.In conclusion: the pacemaker cells, atrial myocytes, ventricular myocytes, AV bundle branches and Purkinje fibres— all conduct action potentials and do not act as wires. But the current flow through gap junctions is more like flow along a wire.
Identify mechanisms that regulate the frequency of the beating heart?
Atrioventricular node (pacemaker of the heart) The action potentials generated by the SA node spread throughout the atria primarily by cell-to-cell conduction at a velocity of about 0.5 m/sec. There is some functional evidence for the existence of specialized conducting pathways within the atria (termed internodal tracts), although this is controversial. As the wave of action potentials depolarizes the atrial muscle, the cardiomyocytes contract by a process termed excitation-contraction coupling. Normally, the only pathway available for action potentials to enter the ventricles is through a specialized region of cells (atrioventricular node, or AV node) located in the inferior-posterior region of the interatrial septum. The AV node is a highly specialized conducting tissue (cardiac, not neural in origin) that slows the impulse conduction considerably (to about 0.05 m/sec) thereby allowing sufficient time for complete atrial depolarization and contraction (systole) prior to ventricular depolarization and contraction. The impulses then enter the base of the ventricle at the Bundle of His and then follow the left and right bundle branches along the interventricular septum. These specialized fibers conduct the impulses at a very rapid velocity (about 2 m/sec). The bundle branches then divide into an extensive system of Purkinje fibers that conduct the impulses at high velocity (about 4 m/sec) throughout the ventricles. This results in rapid depolarization of ventricular myocytes throughout both ventricles.
Sequence of cardiac impulses?
ormally, the only pathway available for action potentials to enter the ventricles is through a specialized region of cells (atrioventricular node, or AV node) located in the inferior-posterior region of the interatrial septum. The AV node is a highly specialized conducting tissue (cardiac, not neural in origin) that slows the impulse conduction considerably (to about 0.05 m/sec) thereby allowing sufficient time for complete atrial depolarization and contraction (systole) prior to ventricular depolarization and contraction. The impulses then enter the base of the ventricle at the Bundle of His and then follow the left and right bundle branches along the interventricular septum. These specialized fibers conduct the impulses at a very rapid velocity (about 2 m/sec). The bundle branches then divide into an extensive system of Purkinje fibers that conduct the impulses at high velocity (about 4 m/sec) throughout the ventricles. This results in rapid depolarization of ventricular myocytes throughout both ventricles. The conduction system within the heart is very important because it permits a rapid and organized depolarization of ventricular myocytes that is necessary for the efficient generation of pressure during systole. The time (in seconds) to activate the different regions of the heart are shown in the figure to the right. Atrial activation is complete within about 0.09 sec (90 msec) following SA nodal firing. After a delay at the AV node, the septum becomes activated (0.16 sec). All the ventricular mass is activated by about 0.23 sec.
It is essential for the heart muscle to beat in a coordinated fashion. what cell junction is best for it?
The coordination is provided by the sinoatrial (SA) node, which is located above the right atrium. What happens is this region of myocytes (heart cells) provides a constant build up of the funny current and acts as a pacemaker for the heart. The funny current was named because scientists who discovered found it funny: "[it] is a mixed Na+ and K+ inward current activated by hyperpolarization". Heart rate can be modified by a variety of neurotransmitters like epinephrine, which increase heart rate by altering the funny current. Hyperpolarization causes action potentials run down the right atrium to another site called the atrioventricular (AV) node. So first, the right atrium contracts. Now the action potentials run down the heart via the Purkinje fibers (the central wall of the heart) and leads down to the ventricles. Think about the order where the blood is going: You first need to pump the blood from the atria to the ventricles before the ventricle pump the blood out to the aorta (left ventricle) or to the lungs (right ventricle). The first to relax is the atria and the cycle repeats, which makes efficiency much higher for the heart. It IS essential for the heart to beat with coordination. Think about blood flow. The blood needs to be pumped but you cannot pump blood that isn't in a compartment. There is an order involved. The cell junction that is best for coordinating the heart is the SA node. Hope this helps.