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There are three types of muscle tissue: skeletal, cardiac, and smooth muscle. Skeletal muscles are attached to the bones of the skeleton and are under voluntary control. They are the most common type of muscle in the body and make up 30-40% of our total body mass. They are responsible for a wide range of movements and functions, including breathing, eating, and moving our bones. Cardiac muscle cells are located in the walls of the heart and are under involuntary control. Smooth muscle fibers are found in the walls of hollow visceral organs like the liver, pancreas, and intestines. They are also under involuntary control. Skeletal and cardiac muscles are striated muscles, meaning they have a striped appearance due to the arrangement of sarcomeres, which are basic contractile units. Smooth muscles, on the other hand, are not striated as they lack sarcomeres.
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What You'll Learn
Skeletal muscle is striated
Skeletal muscle fibres are red and white and appear striped under a microscope due to the arrangement of sarcomeres. These sarcomeres are the repeating functional units of striated muscle tissue. Each muscle fibre contains sarcolemma, sarcoplasm, and sarcoplasmic reticulum. The functional unit of a muscle fibre is called a sarcomere, and each muscle cell contains myofibrils composed of actin and myosin myofilaments.
The striated appearance of skeletal muscle is due to the presence of T-tubules, which enable the release of calcium ions from the sarcoplasmic reticulum. This release of calcium ions drives the movement of myosin and actin filaments, causing the sarcomere to shorten and the muscle to contract. These contractions enable breathing, movement, and posture maintenance.
Skeletal muscles are also capable of regeneration through a three-phase process involving satellite cells, which are dormant in all healthy skeletal muscle tissue. This process begins with the necrosis of damaged muscle fibres, inducing an inflammatory response. Macrophages then induce phagocytosis of the cell debris and secrete anti-inflammatory cytokines, terminating the inflammation. Finally, the satellite cells re-enter the cell cycle to multiply and differentiate, leading to the maturation and remodelling of newly formed myofibrils.
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Cardiac muscle is striated
Muscle tissue is classified into three types according to structure and function: striated (skeletal), smooth, and cardiac. Striated muscle, also referred to as skeletal muscle, is attached to bones, and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body.
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).
The cardiac muscle contracts in a similar manner to skeletal muscle, although with some important differences. 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. The rise in calcium causes the cell's myofilaments to slide past each other in a process called excitation-contraction coupling.
Cardiac muscle cells (also called cardiomyocytes) are the contractile myocytes of the cardiac muscle. The cells are surrounded by an extracellular matrix produced by supporting fibroblast cells. Cardiomyocytes attach to one another with specialized cell junctions called intercalated discs. Attached cells form long, branching cardiac muscle fibers that are, essentially, a mechanical and electrochemical syncytium allowing the cells to synchronize their actions.
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Smooth muscle is not striated
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It is also found in invertebrates and is controlled by the autonomic nervous system. Smooth muscle is non-striated, meaning it has no sarcomeres and therefore no striations (bands or stripes).
Smooth muscle is found in the walls of hollow organs, including the stomach, intestines, bladder, and uterus. It is also found in the walls of blood vessels and lymph vessels (excluding blood and lymph capillaries), where it is known as vascular smooth muscle. Smooth muscle is present in the tracts of the respiratory, urinary, and reproductive systems. In the eyes, the ciliary muscles, iris dilator muscle, and iris sphincter muscle are types of smooth muscle.
Smooth muscle differs from skeletal muscle in that it is controlled involuntarily by the nervous system. It also has greater elasticity and functions within a larger length-tension curve than striated muscle. Smooth muscle does not contain the protein troponin; instead, calmodulin, caldesmon, and calponin are significant proteins expressed within smooth muscle. Tropomyosin is present in smooth muscle, but its function is unknown.
The thin filaments that are part of the contractile machinery in smooth muscle are predominantly composed of alpha-actin and gamma-actin. Smooth muscle alpha-actin is the predominant isoform within smooth muscle. Actin and myosin are the main proteins involved in muscle contraction. The ratio of actin to myosin in smooth muscle is between 2:1 and 10:1, while in striated skeletal muscle, the ratio is between 1:2 and 1:3.
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Striated muscles have a striped appearance
Skeletal muscles, also known as striated muscles, are the most common type of muscle in the human body, comprising 30% to 40% of total body mass. They are attached to the bones of the skeleton and allow for a wide range of movements and functions. These include breathing, eating, and moving bones, making them vital to everyday activities.
The contraction of striated muscles results from the ATP-dependent rowing motion of the myosin heads, causing a shift of the actin filaments. This process is regulated by calcium ions, which are released from the sarcoplasmic reticulum through T-tubules. The calcium ions drive the movement of myosin and actin filaments, leading to muscle contraction.
Striated muscles consist of two types of tissues: skeletal muscle and cardiac muscle. Skeletal muscles are under voluntary control, while cardiac muscles, found in the walls of the heart, are under involuntary control. Both types of striated muscles have a "striated" appearance due to their densely packed myofibrils. However, they differ in their histology and physiology.
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Striated muscles are part of the musculoskeletal system
Striated muscles, also known as skeletal muscles, are indeed part of the musculoskeletal system. They are the most common type of muscle in the body, comprising 30% to 40% of total body mass. These muscles are attached to the bones of the skeleton and are responsible for a wide range of movements and functions. They are called striated muscles because, under a microscope, they exhibit a striped appearance due to the arrangement of sarcomeres, which are the basic contractile units.
Skeletal muscles are made up of flexible muscle fibres that can range from less than half an inch to just over 3 inches in diameter. These fibres contract, enabling the muscles to move the bones and facilitating various movements. Each muscle can contain thousands of fibres, and these fibres are surrounded by connective tissue layers called fascia. The outermost layer is called the epimysium, which provides structural integrity to the muscle during contractions. The middle layer is the perimysium, which surrounds bundles of muscle fibres. The innermost layer is the endomysium, which encases individual muscle fibres.
The skeletal muscles are under voluntary control, meaning an individual can control how and when they work. They play a vital role in everyday activities, including breathing, eating, and moving. For example, the skeletal muscles enable the expansion and contraction of the chest cavity during inhalation and exhalation. Additionally, skeletal muscles can regenerate better than cardiac muscles due to the presence of satellite cells, which are dormant in healthy skeletal muscle tissue.
The skeletal musculature is also part of the locomotor system, responsible for moving and stabilising the skeleton. They are attached to the bones by collagen-rich tendons, and their contractions enable the body to maintain posture and perform various physical tasks.
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Frequently asked questions
Striated muscles are a type of muscle tissue that features repeating functional units called sarcomeres. They are called striated muscles because, under a microscope, the sarcomeres are visible along muscle fibres, giving a striped appearance to the tissue. The two types of striated muscle are skeletal muscle and cardiac muscle.
Skeletal muscles are attached to the bones of the skeleton and are under voluntary control. They are the most common type of muscle in the body and make up 30-40% of total body mass. Skeletal muscles allow you to perform a wide range of movements and functions.
Cardiac muscles are a type of striated muscle tissue found only in the heart. Their main function is heart contraction, which pumps blood throughout the body.
Smooth muscles are the third type of muscle tissue, along with skeletal and cardiac. They are found in the walls of hollow visceral organs such as the liver, pancreas, and intestines. Smooth muscles are not striated because they do not contain sarcomeres.
