Dominic Stone
Cardiac muscle cells are uninucleate and involuntary. They are found only in the heart and are branched and cylindrical in shape. Cardiac muscle cells are specialized excitable cells that can induce electrical impulses and give rise to action potentials. Unlike skeletal muscle cells, which are multinucleated, cardiac muscle cells did not fuse together during development. Instead, they are connected via intercalated discs and gap junctions, resulting in their functional synchronism.
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What You'll Learn
Cardiac muscle cells are uninucleate and involuntary
Cardiac muscle cells have a single nucleus, unlike skeletal muscle cells, which are multinucleated. This is due to the different ways in which these muscle types develop. During development, cardiac myocytes do not fuse together like skeletal muscle cells do; instead, they are connected via intercalated discs and gap junctions. This is why cardiac and smooth muscle are referred to as functional synchronism, whereas skeletal muscle is considered a true synchronism.
The function of cardiac muscle cells is to produce force and motion, specifically in the context of the heart. Their ability to induce electrical impulses is critical for the proper functioning of the heart. The contraction and relaxation of cardiac muscles are similar to that of skeletal muscles but with some distinct differences.
In contrast to cardiac and smooth muscle, skeletal muscle is also known as voluntary muscle. It is attached to bones and tendons, regulating locomotion and maintaining body posture. All voluntary actions of the body are controlled by skeletal muscles. Smooth muscles, on the other hand, are involuntary and found within the inner lining of organs such as the stomach, oesophagus, intestines, and blood vessels. They are not under conscious control like skeletal muscles.
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Cardiac muscle is smooth
The human body is made up of thousands of muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. There are three types of muscle tissue in the human body: smooth muscle, skeletal muscle, and cardiac muscle.
Cardiac muscle, also called the myocardium, is found only in the heart. It is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force to pump blood to supply the metabolic demands of the entire body. The heart is made up of three layers—the pericardium, myocardium, and endocardium—and it is only the myocardium that is composed of cardiac muscle.
Cardiac muscle is also an involuntary muscle, like smooth muscle. This means that its contractions are not under conscious control. Skeletal muscle, on the other hand, is voluntary, and its contractions are under conscious control.
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Cardiac muscle is striated
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 forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium).
Cardiac muscle cells, also known as cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Under a microscope, cardiac muscle cells appear roughly rectangular and are joined at their ends by intercalated discs to form long fibres. Each cell contains myofibrils, specialised protein contractile fibres of actin and myosin that slide past each other. These are organised into sarcomeres, the fundamental contractile units of muscle cells.
The regular organisation of myofibrils into sarcomeres gives cardiac muscle cells a striped or striated appearance when viewed through a microscope, similar to skeletal muscle. These striations are caused by lighter I bands composed mainly of actin and darker A bands composed mainly of myosin. Unlike skeletal muscle fibres, cardiomyocytes are single cells typically with a single centrally located nucleus. A principal characteristic of cardiomyocytes is that they contract on their own intrinsic rhythms without any external stimulation.
Specialised modified cardiomyocytes known as pacemaker cells set the rhythm of the heart contractions. They are only weakly contractile without sarcomeres and are connected to neighbouring contractile cells via gap junctions. They are located in the sinoatrial node (the primary pacemaker) on the wall of the right atrium, near the entrance of the superior vena cava. Other pacemaker cells are found in the atrioventricular node (secondary pacemaker).
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Cardiac muscle is branched and cylindrical
Cardiac muscle, also called the myocardium, is one of three major muscle categories found in the human body, the other two being smooth muscle and skeletal muscle. Each cardiac muscle cell, or cardiomyocyte, contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma contains voltage-gated calcium channels, which are specialized ion channels that skeletal muscles do not possess.
Cardiac muscle cells are striated, branched, and contain many mitochondria. They are cylindrical and uninucleate in shape, and are found only in the heart. The cardiac cells of the heart are specialized excitable cells that can induce electrical impulses and give rise to the action potential. The action potential lasts approximately 200 ms and is divided into 5 phases: resting, upstroke, early repolarization, plateau, and final repolarization.
The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The cardiac muscle must contract with enough force to pump blood into circulation and supply the metabolic demands of the entire body.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. The interactions between these filaments form the basis of the sliding filament theory. Gap junctions between adjacent cardiomyocytes allow for the propagation of coordinated action potentials from one cell to the next, in a phenomenon known as electrical coupling.
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Cardiac muscle is found only in the heart
The human body has three major categories of muscles: smooth muscle, skeletal muscle, and cardiac muscle. Cardiac muscle, also called myocardium or heart muscle, is found only in the heart. It forms the thick middle layer of the heart, between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium is not cardiac muscle but is made up of simple squamous epithelial cells that form the inner lining of the heart chambers and valves.
Cardiac muscle is an involuntary, striated muscle that constitutes the main tissue of the wall of the heart. It is composed of individual cardiac muscle cells called cardiomyocytes, which are joined by intercalated discs and encased by collagen fibres and other substances that form the extracellular matrix. Cardiomyocytes are the contractile cells of the heart, and their primary function is to contract, generating the pressure needed to pump blood through the circulatory system. The contraction and relaxation of cardiac muscle are similar to that of skeletal muscle but with some differences. For instance, cardiac cells can induce electrical impulses and give rise to action potentials, which are vital for pumping blood throughout the cardiovascular system.
Cardiomyocytes are tubular structures composed of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. The thick myofilaments contain the protein myosin, while the thin myofilaments contain the protein actin. The sliding of actin and myosin past each other produces the formation of "cross-bridges", which causes contraction of the heart and the generation of force.
Cardiac muscle cells contain voltage-gated calcium channels, which are specialized ion channels that skeletal muscles do not possess. Calcium plays a crucial role in the contraction of cardiac muscle. Electrical stimulation triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum, leading to excitation-contraction coupling and subsequent muscle contraction.
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Frequently asked questions
Yes, cardiac muscles are uninucleate.
Being uninucleate means having a single nucleus per cell.
Cardiac muscles are involuntary, smooth, striated, and cylindrical in shape.
Cardiac muscles are found only in the heart.
