Victor Forge
Cardiac muscle, also known as myocardium, is one of three types of muscle tissues found in the human body, the others being skeletal muscle and smooth muscle. It is composed of individual cardiac muscle cells, or cardiomyocytes, joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. The cardiac muscle is responsible for the contractility of the heart, which is the basis for its pumping action. This involuntary muscle tissue is highly specialised and only found in the heart, where it is involved in coordinated contractions to allow the heart to pump blood through the circulatory system.
| Characteristics | Values |
|---|---|
| Types | One of three types of muscle tissues, the others being skeletal muscle and smooth muscle |
| Location | Only found in the heart |
| Involuntary control | Yes |
| Striated | Yes |
| Rhythmic contractions | Yes |
| Contractility | Yes |
| Electrical impulses | Yes |
| Calcium release | Yes |
| T-tubules | Yes |
| Intercalated discs | Yes |
| Gap junctions | Yes |
| Desmosomes | Yes |
| Pacemaker cells | Yes |
Explore related products
What You'll Learn
Contracting and pumping blood
The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac cycle consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, and one during which there is a period of robust contraction and pumping of blood, called systole.
The cardiac muscle contracts and relaxes 60-100 times per minute, from intrauterine life until death, without rest. The cardiac muscle in the wall of the left ventricle has a particularly heavy workload, forcing oxygenated arterial blood around the body. The contractile cells demonstrate a much more stable resting phase than conductive cells at approximately −80 mV for cells in the atria and −90 mV for cells in the ventricles.
The myocardial contractile cells constitute 99% of the cells in the atria and ventricles. These contractile cells conduct impulses and are responsible for contractions that pump blood through the body. When stimulated by an action potential, voltage-gated channels rapidly open, beginning the positive-feedback mechanism of depolarization. The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments toward each other, causing the cell to shrink.
The cardiac muscle cells contain branched fibres connected via intercalated discs that contain gap junctions and desmosomes. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump.
Cycling and Muscle Hypertrophy: Is There a Link?
You may want to see also
Explore related products
Involuntary control
The human body has three major categories of muscles: cardiac, smooth, and skeletal. Cardiac muscle, also called the myocardium, is located in the walls of the heart and is responsible for the contractility of the heart and, therefore, the pumping action.
Cardiac muscle is under involuntary control. This means that it is not under conscious control. Instead, it is controlled by the autonomic nervous system and functions involuntarily to maintain the body's metabolic demands. The generation of a cardiac action potential is involuntary and proceeds via a process known as excitation-contraction coupling (ECC). Action potentials travel along the sarcolemma (the cardiomyocyte plasma membrane) and into the t-tubules to depolarize the membrane.
The cardiac muscle cell has one central nucleus, like smooth muscle, but it is also striated, like skeletal muscle. The striations in cardiac muscle are due to the presence of sarcomeres, which are the functional unit of cardiomyocyte contraction. Sarcomeres consist of thick (myosin) and thin (actin) filaments, the interactions of which form the basis of the sliding filament theory. The cardiac muscle cells (cardiomyocytes) are also branched and contain many mitochondria.
The t-tubules are highly branched invaginations of the cardiomyocyte sarcolemma that function in ECC, action potential initiation and regulation, maintaining the resting membrane potential, and signal transduction. T-tubules regulate the cardiac ECC by concentrating voltage-gated L-type calcium channels. These calcium channels are specialized ion channels that skeletal muscle does not possess. The released calcium attaches to troponin C, causing tropomyosin to detach from the myosin-binding sites on actin. Actin and myosin then form a cross-bridge, and contraction occurs.
Magnesium: Muscle Relaxant and Spasms Solution
You may want to see also
Explore related products
Generating force
The primary function of cardiac muscle is to pump oxygenated blood into circulation by generating sufficient force. The mechanism behind each coordinated contraction involves the cardiac muscle and electrical impulses. These contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
Cardiac muscle, also called heart muscle or myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. The cardiac muscle (myocardium) forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium), with blood supplied via the coronary circulation.
The cardiac output is determined by the contractile force developed by the cardiac muscle cells, as well as by the frequency at which they are activated (rhythmicity). The factors affecting the frequency and force of heart muscle contraction are critical in determining the normal pumping performance of the heart and its response to changes in metabolic demand. The contractile units of the cardiac muscle are called sarcomeres. The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments, the interactions between which form the basis of the sliding filament theory.
The sliding filament theory describes the process by which the myosin and actin filaments slide past each other during muscle contraction. This process is made possible by the presence of calcium ions (Ca2+) within the muscle cell. The release of calcium from the sarcoplasmic reticulum, the cell's internal calcium store, causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling. This process is essential for muscle contraction and relaxation, as it allows the muscle fibres to generate force and return to their resting length.
Treating Tender Muscles: Effective Strategies for Quick Recovery
You may want to see also
Explore related products
Electrical coupling
Cardiac muscle is capable of electrical coupling. This property is known as autorhythmicity. Autorhythmicity is the ability of cardiac muscle to initiate an electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger the contractile mechanism. This is a unique property of cardiac muscle, as neither smooth nor skeletal muscle can do this.
The contractile functions of the heart involve electrical impulses and require ATP. The cardiac action potential lasts approximately 200 ms and is divided into five phases: resting, upstroke, early repolarization, plateau, and final repolarization. The resting phase is much more stable in contractile cells than in conductive cells, at approximately −80 mV for cells in the atria and −90 mV for cells in the ventricles.
The contractile cells then undergo rapid depolarization, followed by a plateau phase and then repolarization. This accounts for the long refractory periods required for the cardiac muscle cells to pump blood effectively before they are capable of firing for a second time. These cardiac myocytes normally do not initiate their own electrical potential but are capable of doing so. Instead, they wait for an impulse to reach them. When stimulated by an action potential, voltage-gated channels rapidly open, beginning the positive-feedback mechanism of depolarization.
The pacemaker cells, which include sinoatrial (SA) and atrioventricular (AV) nodes, are also involved in electrical coupling. These cells can initiate their own electrical activity and send signals throughout the heart without requiring external stimulation. This autorhythmicity is due to the presence of "funny" current channels, which allow sodium ions to leak continuously into the cell, slowly raising the membrane potential until depolarization occurs.
Lift, Firm, and Shape Your Glutes: A Guide
You may want to see also
Explore related products
Recovering from excitation
Cardiac muscle, also known as heart muscle or myocardium, is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the heart wall. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The mechanism behind each coordinated contraction involves the cardiac muscle and electrical impulses. These contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones.
The contractile force developed by the cardiac muscle cells, as well as the frequency at which they are activated (rhythmicity), determine the cardiac output. The factors affecting the frequency and force of heart muscle contraction are critical in determining the normal pumping performance of the heart and its response to changes in demand.
Cardiac excitability is the ability of cardiac cells to depolarize and repolarize during the action potential, as well as the ease with which electrical activity propagates from cell to cell. The action potential (activation of the muscle) is divided into five phases, each caused by time-dependent changes in the permeability of the plasma membrane to potassium ions (K+), sodium ions (Na+), and calcium ions (Ca2+).
The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling (ECC). Electrical stimulation in the form of a cardiac action potential triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum. This process is known as calcium-induced calcium release (CICR).
T-tubules in cardiac muscle play a crucial role in excitation-contraction coupling by rapidly transmitting electrical impulses (action potentials) from the cell surface to the cell's core and helping to regulate calcium concentration within the cell.
In summary, recovering from excitation in cardiac muscle involves the regenerative depolarization and repolarization of cardiac cells during the action potential, facilitated by the movement of ions and the release of calcium, which triggers muscle contraction and ultimately results in the pumping of blood into circulation.
Muscle Repair: The Power of Proteins
You may want to see also
Frequently asked questions
Yes, cardiac muscle contracts involuntarily. This is one of the features that differentiate it from skeletal muscle, which is under voluntary control.
Yes, the primary function of cardiac muscle is to pump blood into circulation by generating sufficient force.
No, cardiac muscle is not capable of self-repair. Any structural changes or defects during the development of the heart can lead to congenital heart disorders.
Yes, exercise can strengthen the cardiac muscle and reduce the risk of developing cardiomyopathy.
