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Muscle tissue can be divided into three types: skeletal, cardiac, and smooth. Skeletal muscles are under voluntary control, while cardiac and smooth muscles are involuntary. Cardiac muscle tissue is found only in the heart, where it pumps blood throughout the body and maintains blood pressure. Unlike skeletal muscle, cardiac muscle is not consciously controlled. It is also differentiated by the presence of intercalated discs that control the synchronized contraction of cardiac tissues. Cardiac myocytes are shorter and contain only one or two centrally located nuclei. Smooth muscle tissue, on the other hand, is found in numerous organs and tissue systems, such as the digestive and respiratory systems. This type of muscle is also known as non-striated muscle, as it lacks distinct dark and light bands on its surface, giving it a smooth appearance. So, is cardiac muscle non-striated?
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What You'll Learn
Cardiac muscle is striated
Muscle tissue is categorised into three types based on structure and function: striated (skeletal), smooth, and cardiac. Cardiac muscle, also known as myocardium or heart muscle, is one of the three types of vertebrate muscle tissues. It is an involuntary, striated muscle that makes up the heart wall's primary tissue.
Cardiac muscle is found only in the heart, where contractions pump blood throughout the body and maintain blood pressure. It is similar to skeletal muscle in that it contracts in the same way. However, it is not consciously controlled and is therefore classified as involuntary. Cardiac muscle can be distinguished from skeletal muscle by the presence of intercalated discs, which allow for the synchronised contraction of cardiac tissues. Cardiac myocytes are shorter than skeletal muscle fibres and usually contain only one or two centrally located nuclei.
The cardiac muscle's sheets of muscle fibres wrap around the left ventricle closest to the endocardium and are oriented perpendicularly to those closest to the epicardium. When these sheets contract in a coordinated manner, they allow the ventricle to squeeze in several directions at once. This includes longitudinally (becoming shorter from apex to base), radially (becoming narrower from side to side), and with a twisting motion, similar to wringing out a damp cloth. This maximises the amount of blood squeezed out of the heart with each heartbeat.
Cardiac muscle cells, or cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are surrounded by an extracellular matrix produced by supporting fibroblast cells. Cardiomyocytes are joined 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 under a microscope.
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Cardiac muscle is involuntary
Cardiac muscle tissue, or myocardium, is a type of muscle tissue that forms the vertebrate heart. It is involuntary, meaning it is not under conscious control. Instead, it contracts and relaxes involuntarily, keeping the heart pumping blood around the body.
Cardiac muscle cells, also called cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are responsible for the highly coordinated actions that keep the heart pumping and blood circulating throughout the body. Each cardiomyocyte needs to contract in coordination with its neighbouring cells, working together to efficiently pump blood from the heart. If this coordination breaks down, the heart may not pump at all, as can occur during abnormal heart rhythms such as ventricular fibrillation.
The heart also contains specialised types of cardiac tissue containing "pacemaker" cells. These contract and expand in response to electrical impulses from the nervous system. Pacemaker cells generate electrical impulses, or action potentials, that tell cardiac muscle cells to contract and relax. They are distributed throughout the heart and are responsible for several functions. Firstly, they are responsible for being able to spontaneously generate and send out electrical impulses. They set the rhythm of the heart contractions and control heart rate, determining how fast the heart pumps blood.
Cardiac muscle is striated, meaning it appears striped or striated under a microscope. These stripes occur due to alternating filaments that comprise myosin and actin proteins. The dark stripes indicate thick filaments that comprise myosin proteins, while the thin, lighter filaments contain actin. When a cardiac muscle cell contracts, the myosin filament pulls the actin filaments toward each other, causing the cell to shrink. The cell uses ATP to power this contraction.
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Cardiac muscle is found only in the heart
There are three types of muscle tissue in the human body: skeletal, smooth, and cardiac. Cardiac muscle, also called the myocardium, is found only in the heart. It forms the thick middle layer of the heart wall, 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 striated and involuntary. 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. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma contains voltage-gated calcium channels, specialised ion channels that skeletal muscle does not possess. The intercalated discs control the synchronized contraction of cardiac tissues, allowing the heart to work as a pump.
Cardiac muscle cells are the contractile myocytes of the cardiac muscle. They are the functional unit of cardiomyocyte contraction and consist of thick (myosin) and thin (actin) filaments. The interactions between these filaments form the basis of the sliding filament theory. The sliding of actin and myosin past each other produces the formation of "cross-bridges", which causes contraction of the heart and generation of force. The primary function of cardiomyocytes is to contract, which generates the pressure needed to pump blood through the circulatory system.
Cardiac muscle has its own auto-rhythmicity. Unlike smooth or skeletal muscle, which require neural input for contraction, cardiac fibres have their own pacemaker cells that spontaneously depolarize. These depolarizations occur at a consistent pace, but the pacemaker cells can also receive input from the autonomic nervous system to decrease or increase the heart rate depending on the requirements of the body.
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Cardiac muscle is not consciously controlled
Cardiac muscle, also called the myocardium, is one of three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle is striated and involuntary. It is found only in the heart, where it pumps blood throughout the body and maintains blood pressure.
The heart is made up of three layers—the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells that form the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force and with enough blood to supply the metabolic demands of the entire body.
Cardiac muscle cells (cardiomyocytes) are striated, branched, and contain many mitochondria. Each myocyte contains a single, centrally located nucleus surrounded by a cell membrane known as the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialized ion channels that skeletal muscle does not possess. Cardiac muscle cells contain branched fibers 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.
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Cardiac muscle is differentiated from skeletal muscle
Cardiac muscle and skeletal muscle are two distinct types of muscle tissue. They differ in terms of their location, appearance, and function.
Firstly, cardiac muscle is found only in the heart, where it performs cardiac contractions to pump blood throughout the body and maintain blood pressure. On the other hand, skeletal muscles are attached to bones all over the body and facilitate skeletal movements such as locomotion. They are also involved in maintaining posture and balance.
Secondly, both cardiac and skeletal muscles are striated, meaning they exhibit a striped appearance due to the alignment of myofibrils that produce a constant directional tension. However, cardiac myocytes are shorter and contain only one or two centrally located nuclei, while skeletal myocytes are elongated and tubular with multiple peripheral nuclei. Additionally, cardiac muscle can be differentiated from skeletal muscle by the presence of intercalated discs, which facilitate the synchronized contraction of cardiac tissues.
Thirdly, skeletal muscles are under voluntary control, allowing conscious movement of the body. In contrast, cardiac muscles are involuntary, functioning independently without conscious control. The beating of the heart, for example, occurs involuntarily.
In summary, cardiac and skeletal muscles differ in terms of their location, morphology, and function. Cardiac muscle is limited to the heart, exhibits distinct morphological features, and operates involuntarily to facilitate essential bodily functions. Skeletal muscle, on the other hand, is widespread throughout the body, attached to bones, and functions voluntarily to enable conscious movement and maintain posture.
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Frequently asked questions
Non-striated muscles are muscles that have no striations on their surface, meaning they do not have distinct dark and light bands. They are also known as involuntary muscles as they are not under the control of the organism. They are found in the walls of organs such as the oesophagus, stomach, intestines, bronchi, uterus, urethra, bladder and blood vessels.
No, cardiac muscle is striated. It is found only in the heart and is involuntary.
The three types of muscle tissue are skeletal muscle, cardiac muscle and smooth muscle. Skeletal muscle is voluntary and striated, cardiac muscle is involuntary and striated, and smooth muscle is involuntary and non-striated.
