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Muscle is a soft tissue that allows for movement in the body. There are three types of muscle tissue in vertebrates: skeletal, cardiac, and smooth muscle. Each muscle is composed of muscle fibres, which are made up of myofibrils. These myofibrils contain contractile proteins called actin and myosin, which interact to cause movement. This interaction between actin and myosin is the basis for muscle contraction, which is the primary function of muscle.
| Characteristics | Values |
|---|---|
| Muscle tissue types in vertebrates | Skeletal, cardiac, and smooth muscle |
| Muscle tissue types in invertebrates | Transversely striated, obliquely striated, and smooth muscle |
| Skeletal muscle tissue structure | Elongated, striated muscle tissue with muscle fibres that range from 3-8 micrometres in width and 18-200 micrometres in breadth |
| Skeletal muscle fibre composition | Actin and myosin filaments called myofilaments, repeated in units called sarcomeres |
| Sarcomere composition | Actin (thin filaments), myosin (thick filaments), and support proteins |
| Sarcomere structure | M line, Z disc, H band, A band, and I band |
| Myosin type in muscle | Myosin II |
| Myosin II molecule composition | Two heavy chains and two pairs of light chains |
| Myosin II heavy chain composition | Globular head region and a long α-helical tail |
| Myosin II light chain role | Regulatory role at the hinge region |
| Myosin function | Acts as a motor that drives filament sliding during muscle contraction |
| Muscle contraction | Results from the interaction between actin and myosin filaments |
| Muscle energy source | Oxidation of fats and carbohydrates, anaerobic chemical reactions, and creatine phosphate |
| Muscle function | Contraction, producing movement, maintaining posture, body temperature, and joint position, storing nutrients, and secreting signalling molecules |
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Skeletal muscle
Each skeletal muscle is an organ composed of various integrated tissues, including skeletal muscle fibres, blood vessels, nerve fibres, and connective tissue. The muscle fibres are composed of myofibrils, which are made up of actin (thin filaments) and myosin (thick filaments) arranged into functional units called sarcomeres. These sarcomeres give skeletal muscle its striated appearance and are responsible for muscle contraction. The actin and myosin filaments interact with each other and with other proteins to generate force and cause movement.
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Cardiac muscle
The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The inner endocardium lines the cardiac chambers, covers the cardiac valves, and joins with the endothelium that lines the blood vessels that connect to the heart. The outer epicardium forms part of the pericardial sac that surrounds, protects, and lubricates the heart.
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Smooth muscle
The shape of smooth muscle is described as fusiform, round in the center, and tapering at each end. It has greater elastic properties than striated muscle, which is important in organ systems like the urinary bladder, where contractile tone must be preserved. Smooth muscle can tense and relax, and its cells contain actin and myosin filaments that form continuous chains anchored at dense bodies. These filaments stretch to adjacent smooth muscle cells, forming a mesh-like network that allows for uniform contraction in a spiral corkscrew fashion.
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Muscle contraction
The process of muscle contraction begins with a signal from the nervous system, specifically the motor neuron. This signal, known as an action potential, travels through the nerve cells and reaches the muscle fibres. The action potential causes the release of acetylcholine, a neurotransmitter, at the neuromuscular junction. Acetylcholine binds to receptors on the muscle fibre membrane, initiating a series of chemical reactions.
The binding of acetylcholine opens membrane channels, allowing an influx of sodium ions into the muscle fibre. This sodium influx triggers the release of stored calcium ions, which then diffuse into the muscle fibre. Calcium ions play a crucial role in muscle contraction by producing attractive forces between actin and myosin filaments, causing them to slide alongside each other. This sliding movement leads to the contractile process.
Actin and myosin filaments are the key proteins involved in muscle contraction. They are arranged in repeating units called sarcomeres, which give skeletal muscle its striated appearance. The interaction between actin and myosin filaments results in the shortening of the muscle fibres, leading to contraction. This contraction occurs through a cycle of dissociation and binding between the filaments, powered by the hydrolysis of ATP.
The contraction continues until calcium levels in the muscle fibre decrease, causing tropomyosin to cover the actin filaments' myosin-binding sites, preventing further interaction. When the nervous system signal ceases, the chemical reactions reverse, leading to muscle relaxation. The muscle fibres return to a low-tension state, and the contraction process is complete.
It is important to note that there are different types of muscle tissues in vertebrates: skeletal, cardiac, and smooth muscle. Skeletal muscle contraction is typically voluntary and is responsible for body movements, while cardiac and smooth muscle contract involuntarily. Understanding the intricate process of muscle contraction is essential for comprehending the mechanics of movement and the functioning of the muscular system.
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Muscle disorders
There are many causes of muscle disorders, including genetic mutations, immune system disorders, and nerve damage. In some cases, the cause of muscle disorders is unknown. Muscle disorders can be treated with medications, physical therapy, occupational therapy, and, when necessary, surgery. However, there is currently no cure for neuromuscular disorders. Research is being conducted on genetic therapies and new medications to find a cure.
Skeletal muscle is a type of muscle tissue found in vertebrates that is responsible for movement and posture. It is composed of bundles of muscle fibers called myofibers, which contain several myofibrils. These myofibrils are made up of contractile proteins called actin and myosin, which interact to cause movement. Skeletal muscle is typically anchored to bones by tendons and is under voluntary control, receiving neural inputs that allow for conscious movement.
Smooth muscle and cardiac muscle are also types of muscle tissue found in vertebrates. Smooth muscle is non-striated and involuntary, found within the walls of organs such as the esophagus, stomach, and intestines. Cardiac muscle is found only in the walls of the heart and is also involuntary. These muscle types may be activated through the central nervous system or by innervation from the peripheral plexus or endocrine system.
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Frequently asked questions
Muscle molecules are the proteins and filaments that make up the contractile units of muscle fibres, known as sarcomeres. These include actin, myosin, titin, and nebulin.
There are three types of muscle molecules or contractile proteins: actin (thin filaments), myosin (thick filaments), and support proteins such as titin and nebulin.
During muscle contraction, the actin and myosin filaments slide past each other, with actin moving into the A band and H zone. This interaction generates movement, resulting in the shortening of the sarcomere.
Muscle molecules are responsible for muscle contraction, which is the primary function of muscles. This contraction results in movement, posture control, and the production of body heat.
Muscle molecules are powered by the oxidation of fats and carbohydrates, as well as anaerobic chemical reactions, particularly in fast-twitch fibres. These reactions produce adenosine triphosphate (ATP) molecules, which power the movement of the myosin heads.
